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WO2025008799A1 - Reciprocity precoding scheme selection using time domain channel properties (tdcp) feedback - Google Patents

Reciprocity precoding scheme selection using time domain channel properties (tdcp) feedback Download PDF

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Publication number
WO2025008799A1
WO2025008799A1 PCT/IB2024/056653 IB2024056653W WO2025008799A1 WO 2025008799 A1 WO2025008799 A1 WO 2025008799A1 IB 2024056653 W IB2024056653 W IB 2024056653W WO 2025008799 A1 WO2025008799 A1 WO 2025008799A1
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WIPO (PCT)
Prior art keywords
wireless device
reciprocity
amplitude
channel
network node
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PCT/IB2024/056653
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French (fr)
Inventor
Keerthi Kumar NAGALAPUR
Fredrik Athley
Siva Muruganathan
Per ERNSTRÖM
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Telefonaktiebolaget LM Ericsson AB
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Telefonaktiebolaget LM Ericsson AB
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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0686—Hybrid systems, i.e. switching and simultaneous transmission
    • H04B7/0695—Hybrid systems, i.e. switching and simultaneous transmission using beam selection
    • H04B7/06952—Selecting one or more beams from a plurality of beams, e.g. beam training, management or sweeping
    • H04B7/06966—Selecting one or more beams from a plurality of beams, e.g. beam training, management or sweeping using beam correspondence; using channel reciprocity, e.g. downlink beam training based on uplink sounding reference signal [SRS]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
    • H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
    • H04B7/0619—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal using feedback from receiving side
    • H04B7/0621—Feedback content
    • H04B7/063—Parameters other than those covered in groups H04B7/0623 - H04B7/0634, e.g. channel matrix rank or transmit mode selection

Definitions

  • the present disclosure relates to wireless communications, and in particular, to reciprocity-based precoding schemes.
  • 3GPP Third Generation Partnership Project
  • 4G also referred to as Long Term Evolution (LTE)
  • 5G also referred to as New Radio (NR)
  • Such systems provide, among other features, broadband communication between network nodes, such as base stations, and mobile user equipment (UE) or wireless devices (WD), as well as communication between network nodes and between UEs.
  • 4G also referred to as Long Term Evolution (LTE)
  • 5G also referred to as New Radio (NR) wireless communication systems.
  • Such systems provide, among other features, broadband communication between network nodes, such as base stations, and mobile user equipment (UE) or wireless devices (WD), as well as communication between network nodes and between UEs.
  • UE mobile user equipment
  • WD wireless devices
  • the 3GPP is also developing standards for Sixth Generation (6G) wireless communication networks.
  • 6G Sixth Generation
  • the 5G mobile wireless communication system or NR supports a diverse set of use cases and a diverse set of deployment scenarios.
  • the later includes deployment at both low frequencies (100s of MHz), and very high frequencies (mm waves in the tens of GHz).
  • NR uses OFDM (Orthogonal Frequency Division Multiplexing) in the downlink (i.e., from a network node, or gNB, to a user equipment (UE) or wireless device). It is also referred to as CP-OFDM (Cyclic Prefix OFDM).
  • OFDM Orthogonal Frequency Division Multiplexing
  • CP-OFDM Cyclic Prefix OFDM
  • both CP-OFDM and DFT-spread OFDM are supported.
  • the basic NR physical resource is a time-frequency grid as illustrated in FIG.1, where each resource element corresponds to one OFDM subcarrier during one OFDM symbol interval.
  • a subcarrier spacing of ⁇ ⁇ ⁇ 15 ⁇ ⁇ ⁇ is shown in FIG.1, different subcarrier spacing values are supported in NR.
  • the supported subcarrier spacing values (also referred to as different numerologies) in NR are given by ⁇ ⁇ ⁇ ⁇ 15 ⁇ 2 ⁇ ⁇ ⁇ ⁇ ⁇ where ⁇ is a non-negative integer.
  • the resource allocation in NR may be described in terms of resource blocks, where a resource block corresponds to one slot (0.5 ms) in the time domain and 12 contiguous subcarriers in the frequency domain. Resource blocks are numbered in the frequency domain, starting with 0 from one end of the system bandwidth.
  • Downlink transmissions are dynamically scheduled, i.e., in each slot the network node transmits downlink control information (DCI) about which wireless device data is to be transmitted to and which resource blocks in the current or a future the data is transmitted on.
  • DCI downlink control information
  • This control signaling is typically transmitted in the first one or two OFDM symbols in each slot in NR.
  • the control information is carried on Physical Control Channel (PDCCH) and data is carried on Physical Downlink Shared Channel (PDSCH).
  • PDCH Physical Control Channel
  • PDSCH Physical Downlink Shared Channel
  • a wireless device first detects and decodes PDCCH and if a PDCCH is decoded successfully, it the decodes the corresponding PDSCH based on the decoded control information in the PDCCH. Uplink data transmissions are also dynamically scheduled using PDCCH. Similar to downlink, a wireless device first decodes uplink grants in PDCCH and then transmits data over the Physical Uplink Shared Channel (PUSCH) based the decoded control information in the uplink grant such as modulation order, coding rate, uplink resource allocation, and etc.
  • PUSCH Physical Uplink Shared Channel
  • Physical Uplink Control Channel is also supported in NR to carry uplink control information (UCI) such as HARQ (Hybrid Automatic Repeat Request) related Acknowledgement (ACK), Negative Acknowledgement (NACK), or Channel State Information (CSI) feedback.
  • UCI uplink control information
  • HARQ Hybrid Automatic Repeat Request
  • NACK Negative Acknowledgement
  • CSI Channel State Information
  • 2D antenna arrays Two-dimensional antenna arrays may be (partly) described by the number of antenna columns corresponding to the horizontal dimension ⁇ ⁇ where the number of antenna rows correspond to the vertical dimension ⁇ ⁇ and the number of dimensions corresponds to different polarizations ⁇ ⁇ . The total number of antennas is thus ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ .
  • an antenna is non-limiting in the sense that it can refer to any virtualization (e.g., linear mapping) of the physical antenna elements.
  • pairs of physical sub-elements could be fed the same signal, and hence share the same virtualized antenna port.
  • An example of a 4x8 array with dual-polarized antenna elements is illustrated in FIG.2 where the two-dimensional antenna array has dual-polarized antenna elements (N ⁇ ⁇ 2 with +45 degree and -45 degree slant polarizations) with n ⁇ ⁇ 8 and n ⁇ ⁇ 4.
  • the antenna element corresponding to the first polarization in the ⁇ -th row and ⁇ -th column is indexed by ⁇ ⁇ ⁇ 1 ⁇ ⁇ ⁇ ⁇ ⁇ ⁇
  • the antenna element corresponding to the second polarization in the ⁇ -th row and ⁇ -th column is indexed by ⁇ ⁇ ⁇ 1 ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ .
  • Precoding may be interpreted as multiplying the signal with different beamforming weights for each antenna prior to transmission.
  • a typical approach is to tailor the precoder to the antenna form factor, i.e.
  • Precoding of which beamforming is a special case, from an antenna array can be considered a matrix operation, where one or more input signals to be transmitted can be individually precoded.
  • the precoding operation can be expressed as ⁇ ⁇ ⁇ ⁇ where the transmitted signals are represented as a set of ⁇ ⁇ symbol streams or layers in ⁇ ; ⁇ ⁇ is the signal transmitted on the ⁇ -th antenna element of the antenna array and ⁇ ⁇ , ⁇ is a complex valued precoding weight corresponding to the ⁇ -th layer and the ⁇ -th antenna element.
  • the ⁇ -th column of the precoding matrix ⁇ , ⁇ ⁇ is the precoding vector corresponding to the ⁇ -th layer.
  • FIG.3 is a diagram of an example of precoding. Under the antenna indexing convention described above, the elements 1 to ⁇ ⁇ ⁇ ⁇ ⁇ of each column of ⁇ correspond to the first polarization, while the elements ⁇ ⁇ ⁇ ⁇ ⁇ 1 to 2 ⁇ ⁇ ⁇ ⁇ of each column of ⁇ correspond to the second polarization.
  • the precoding operation can also be expressed as where ⁇ ⁇ ⁇ is the polarization specific precoder vector containing the weights corresponding to the ⁇ -th layer and the antenna elements of the ⁇ -th polarization.
  • Grid-of-Beams In grid-of-Beams precoding, each symbol stream or layer is transmitted over one or more spatial beams selected from a set of predefined beams. In the model described above, this implies that ⁇ ⁇ ⁇ , the precoding vector for the ⁇ -th layer and ⁇ -th polarization, is selected from a set of predefined vectors.
  • DFT-based precoders A common type of grid-of-beams precoding is to use a DFT-precoder, where the precoder vector used to precode a single-layer transmission using a single-polarized uniform linear array (ULA) with N antennas is defined as where k ⁇ 0,1, ... ON ⁇ 1 is the precoder index and O is an integer oversampling factor.
  • u ⁇ is also referred to as an one dimension (1-D) DFT beam with beam index k. If ULA is along the horizontal dimension, each DFT beam points to an azimuth direction. If ULA is along the vertical dimension, each DFT beam points to an elevation direction.
  • Each precoder corresponds to a DFT beam.
  • a corresponding precoder vector for a two-dimensional uniform planar array (UPA) with N ⁇ antenna ports in one dimension and N ⁇ antenna ports in another dimension can be created by taking the Kronecker product of two precoder vectors as w ⁇ 2-D ⁇ k, l ⁇ ⁇ v ⁇ , ⁇ ⁇ u ⁇ , ⁇ ⁇ u ⁇ , ⁇ , beams in each of the two dimensions, and and O ⁇ are the over sampling factors in two dimensions associated with N ⁇ and N ⁇ , respectively.
  • v ⁇ , ⁇ is also referred to a two dimension (2-D) DFT beam characterized by two beam indices ⁇ k, l ⁇ , one in each dimension.
  • Each precoder corresponds to a 2D DFT beam.
  • Extending the DFT precoder for a dual-polarized UPA may then be performed as where ⁇ ⁇ is a co-phasing factor that may be selected from M-PSK alphabet such
  • a precoder matrix ⁇ for multi-layer transmission may be created by appending columns of DFT precoder vectors as where ⁇ is the number of transmission layers.
  • Such DFT-based precoders are used for instance in NR Type I CSI feedback, where each layer is associated with 2D DFT beam.
  • a network node measures the channel between a wireless device and itself using UL reference signals such as UL SRS, and the measured channel is used to determine a precoder for a downlink transmission under the assumption of channel reciprocity between uplink and downlink.
  • UL reference signals such as UL SRS
  • DL and UL channel is reciprocal.
  • CSI-RS based DL precoder matrix index (PMI) feedback reciprocity-based precoding reduces the feedback overhead in UL and has a smaller delay between measurement of the channel and the application of the precoder.
  • a network node can schedule a wireless device with either single-user multi-input multi-output (SU-MIMO) or multi-user multi- input multi-output (MU-MIMO) transmission.
  • SU-MIMO single-user multi-input multi-output
  • MU-MIMO multi-user multi- input multi-output
  • SU-MIMO a set of DL time and frequency resources are used to transmit DL data to a single wireless device.
  • MU- MIMO the same set of time and frequency resources are used to transmit data to a selected set of multiple users (e.g., wireless devices) using a MU-MIMO precoding scheme.
  • a network node may need to select appropriate number of spatial streams for each wireless device to satisfy the per user requirement and maximize the system performance.
  • ZF precoder One type of reciprocity-based precoding is the so called zero-forcing (ZF) precoder which aims to beamform to the desired wireless device while creating nulls to other co- scheduled wireless devices.
  • ZF precoding matrix is given by ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ where ⁇ is the ⁇ ⁇ ⁇ channel matrix between the network node and the co- scheduled wireless devices.
  • a way to mitigate this problem is to regularize the inverse by adding a multiple of the identity matrix before inverting, i.e., ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ where ⁇ denotes the ⁇ ⁇ ⁇ identity matrix and the regularization factor, ⁇ , is a real scalar.
  • This precoder is sometimes referred to as a regularized ZF precoder.
  • a particular choice of regularization factor is ⁇ ⁇ ⁇ ⁇ ⁇ / ⁇ where ⁇ ⁇ is the receiver noise power and ⁇ is the transmitted power. This solution is referred to as the minimum mean square error (MMSE) precoder.
  • MMSE minimum mean square error
  • a related precoder is the signal-to-leakage-and-noise ratio (SLNR) precoder which, up to a proportionality constant, is given by where ⁇ ⁇ is the precoding vector to the k-th wireless device, L is the set of all co- scheduled wireless devices, ⁇ ⁇ is a right-singular vector of the channel matrix and ⁇ ⁇ is the rresponding singular value.
  • ⁇ ⁇ co ⁇ ⁇ ⁇ ⁇ ⁇ may be interpreted as regularization factor.
  • Sounding Reference Signal (SRS) SRS is supported in NR for uplink channel sounding. Configurable SRS bandwidth is supported in NR.
  • An SRS sequence for an SRS antenna port ⁇ ⁇ at OFDM symbol ⁇ ′ in an SRS resource is a cyclic shifted version of a Zadoff-Chu sequence ⁇ ⁇ , ⁇ ⁇ ⁇ with a group number u ⁇ ⁇ 0,1,...,29 ⁇ and a base sequence number ⁇ ⁇ ⁇ 0,1 ⁇ within the group, i.e., where ⁇ ZC ⁇ is the length of the sequence, ⁇ is the number of RBs configured for the SRS resource, ⁇ s R c B ⁇ 12 is the number sub-carriers per RB, ⁇ ⁇ log2 ⁇ ⁇ TC ⁇ and ⁇ TC ⁇ ⁇ 2,4,8 ⁇ is a configured comb value where the SRS sequence occupies every ⁇ ⁇ cs, ⁇ T C sub-carriers, ⁇ ⁇ ⁇ 2 ⁇ SRS cs,max ⁇ cs,max is a cyclic shift and ⁇ SRS is maximum S RS number of cycl
  • the first two SRS ports are allocated with two different cyclic shifts separated by ⁇ on a same set of sub-carriers (with a same first comb offset) and the last two SRS ports are allocated with the same two different cyclic shifts as the first two SRS ports but on a different set of sub-carriers (with a same second comb offset).
  • SRS can be configured by the network (e.g., network node) to be transmitted periodically, aperiodically on a trigger or in a semi-persistent manner.
  • the network can configure SRS transmission with a periodicity ⁇ ⁇ ⁇ 1, 2, 4, 5, 8, 10, 16, 20, 32, 40, 64, 80, 160, 320, 640, 1280, 2560 ⁇ slots.
  • 3GPP Release 18 (Rel-18) Time domain channel property (TDCP) feedback
  • TDCP Time domain channel property
  • the channel autocorrelation is a direct measure of how fast the channel varies with time.
  • the TDCP feedback report contains the amplitude of the normalized instantaneous autocorrelation function.
  • the normalized amplitude of the TDCP can be given as follows for an autocorrelation delay of ⁇ ⁇ : where h ⁇ ⁇ ⁇ ⁇ is the channel for subcarrier ⁇ at time ⁇ .
  • the geometric average over the two time-instances ⁇ and ⁇ ⁇ ⁇ ⁇ of the zero- delay autocorrelation function is used in order to make the metric robust against automatic gain control (AGC).
  • AGC automatic gain control
  • the absolute value of the instantaneous autocorrelation function is used and this quantity is referred to as the channel correlation amplitude.
  • reciprocity-based precoding schemes can be used instead of wireless device feedback based schemes for wireless devices with sufficient UL SNR.
  • using a reciprocity-based scheme that is sensitive to time-variations of the channel between the wireless device and a network node degrades both the user and the system performance when channel varies.
  • the time-domain channel property (TDCP) feedback, from a wireless device, which contains information related to the degree of time-variation of the channel can be used to select the type of reciprocity-based precoding scheme used.
  • a method implemented by a network node that is configured to communicate with a wireless device is provided. The method comprises selecting a reciprocity precoding scheme based on information related to a degree of time- variation of a channel, the information being associated with the wireless device.
  • the information related to the degree of time-variation of the channel is included in time-domain channel property, TDCP, feedback from the wireless device.
  • the information related to the degree of time-variation of the channel comprises an amplitude of a normalized autocorrelation.
  • the selection of the reciprocity precoding scheme is based on the reciprocity precoding scheme being robust to channel variations.
  • the selection of the reciprocity precoding scheme is based on the reciprocity precoding scheme being robust to channel variations.
  • the selection of the reciprocity precoding scheme is based on the reciprocity precoding scheme being robust to channel variations.
  • the reciprocity precoding scheme that is selected is a grid of beams, GoB, based scheme where a spatial stream towards the wireless device is restricted to a single beam selected from a codebook of spatial beams.
  • the method further comprises at least one of scheduling the wireless device for a single-user multiple-input multiple-output, SU-MIMO, transmission based on the amplitude of the normalized autocorrelation being below a threshold, and scheduling the wireless device for a multi-user MIMO, MU-MIMO, transmission based on the amplitude of the normalized autocorrelation being above a threshold.
  • the method further comprises performing channel prediction corresponding to a future slot based on uplink channels measured across different sounding reference signals, SRSs, instances transmitted by the wireless device based on the amplitude of the normalized autocorrelation being below a threshold.
  • the method further comprises using a regularized precoder based on reciprocity, a regularization factor associated with the regularized precoder being based on the amplitude of the normalized autocorrelation.
  • the regularization factor is inversely proportional to the amplitude of the normalized autocorrelation.
  • the method further comprises performing downlink transmission based on the selected reciprocity precoding scheme.
  • a network node a network node configured to communicate with a wireless device, the network node configured to, and/or comprising a radio interface and/or comprising processing circuitry configured to perform any of the steps of above noted methods, is provided.
  • a method implemented by a wireless device that is configured to communicate with a network node, comprises determining information related to a degree of time-variation of a channel associated with the wireless device, transmitting the information to the network node and receiving a downlink transmission according to a reciprocity precoding scheme that is selected based on the information.
  • the information related to the degree of time-variation of the channel is included in time-domain channel property, TDCP, feedback from the wireless device.
  • the information related to the degree of time-variation of the channel comprises an amplitude of a normalized autocorrelation.
  • the reciprocity precoding scheme that is used for the downlink transmission being robust to channel variations. In some embodiments, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a sounding reference signal, SRS, periodicity is greater than a second predefined threshold, the reciprocity precoding scheme that is used for the downlink transmission being robust to channel variations.
  • the reciprocity precoding scheme that is used for the downlink transmission being robust to channel variations.
  • the reciprocity precoding scheme is based on a grid of beams, GoB, based scheme where a spatial stream towards the wireless device is restricted to a single beam selected from a codebook of spatial beams.
  • the method further comprises receiving at least one of a scheduling of the wireless device for a single-user multiple-input multiple-output, SU-MIMO, transmission based on the amplitude of the normalized autocorrelation being below a threshold and a scheduling of the wireless device for a multi-user MIMO, MU-MIMO, transmission based on the amplitude of the normalized autocorrelation being above a threshold.
  • a wireless device configured to communicate with a network node, the wireless device configured to, and/or comprising a radio interface and/or processing circuitry configured to perform any of the above noted steps is provided.
  • FIG.1 is a diagram of an example of NR physical resources
  • FIG.2 is a diagram of an example of a two-dimensional antenna array of dual polarized antenna elements
  • FIG.3 is a diagram of an example of precoding
  • FIG.4 is a schematic diagram of an exemplary network architecture illustrating a communication system connected via an intermediate network to a host computer according to the principles in the present disclosure
  • FIG.5 is a block diagram of a host computer communicating via a network node with a wireless device over an at least partially wireless connection according to some embodiments of the present disclosure
  • FIG.6 is a flowchart illustrating exemplary methods implemented in a communication system including a host computer, a network node and a wireless device for executing a client application at a wireless device according to some embodiments of the present disclosure
  • FIG.7 is
  • reciprocity-based precoding schemes can be used instead of wireless device feedback based schemes for wireless devices with sufficient UL SNR.
  • using a reciprocity-based scheme that is sensitive to time- variations of the channel between the wireless device and a network node degrades both the user and the system performance when channel varies.
  • how to mitigate such performance degradation in reciprocity based precoding schemes is an unsolved problem.
  • One or more embodiments of the present disclosure solve at least in part this issues with reciprocity-based schemes by, for example, selecting the type of reciprocity-based precoding scheme to be used based on TDCP feedback, from the wireless device, where the TDCP feedback contains information related to the degree of time-variation of the channel.
  • the joining term, “in communication with” and the like may be used to indicate electrical or data communication, which may be accomplished by physical contact, induction, electromagnetic radiation, radio signaling, infrared signaling or optical signaling, for example.
  • electrical or data communication may be accomplished by physical contact, induction, electromagnetic radiation, radio signaling, infrared signaling or optical signaling, for example.
  • the term “coupled,” “connected,” and the like may be used herein to indicate a connection, although not necessarily directly, and may include wired and/or wireless connections.
  • network node can be any kind of network node comprised in a radio network which may further comprise any of base station (BS), radio base station, base transceiver station (BTS), base station controller (BSC), radio network controller (RNC), g Node B (gNB), evolved Node B (eNB or eNodeB), Node B, multi- standard radio (MSR) radio node such as MSR BS, transmission reception point (TRP), scheduler, multi-cell/multicast coordination entity (MCE), integrated access and backhaul (IAB) node, relay node, donor node controlling relay, radio access point (AP), transmission points, transmission nodes, Remote Radio Unit (RRU) Remote Radio Head (RRH), a core network node (e.g., mobile management entity (MME), self-organizing network (SON) node, a coordinating node, positioning node, MDT node, etc.), an external node (e.g., 3rd party node, a node external to the
  • MME mobile management entity
  • the network node may also comprise test equipment.
  • radio node used herein may be used to also denote a wireless device (WD) such as a wireless device (WD) or a radio network node.
  • WD wireless device
  • UE user equipment
  • the WD herein can be any type of wireless device capable of communicating with a network node or another WD over radio signals, such as wireless device (WD).
  • the WD may also be a radio communication device, target device, device to device (D2D) WD, machine type WD or WD capable of machine to machine communication (M2M), low-cost and/or low-complexity WD, a sensor equipped with WD, Tablet, mobile terminals, smart phone, laptop embedded equipped (LEE), laptop mounted equipment (LME), USB dongles, Customer Premises Equipment (CPE), an Internet of Things (IoT) device, or a Narrowband IoT (NB-IOT) device, etc.
  • the generic term “radio network node” is used.
  • Radio network node may comprise any of base station, radio base station, base transceiver station, base station controller, network controller, RNC, evolved Node B (eNB), Node B, gNB, Multi-cell/multicast Coordination Entity (MCE), IAB node, relay node, access point, radio access point, Remote Radio Unit (RRU) Remote Radio Head (RRH).
  • RNC evolved Node B
  • MCE Multi-cell/multicast Coordination Entity
  • IAB node Multi-cell/multicast Coordination Entity
  • RRU Remote Radio Unit
  • RRH Remote Radio Head
  • WCDMA Wide Band Code Division Multiple Access
  • WiMax Worldwide Interoperability for Microwave Access
  • UMB Ultra Mobile Broadband
  • GSM Global System for Mobile Communications
  • functions described herein as being performed by a wireless device or a network node may be distributed over a plurality of wireless devices and/or network nodes.
  • the functions of the network node and wireless device described herein are not limited to performance by a single physical device and, in fact, can be distributed among several physical devices.
  • all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.
  • FIG.4 a schematic diagram of a communication system 10, according to an embodiment, such as a 3GPP-type cellular network that may support standards such as LTE and/or NR (5G), which comprises an access network 12, such as a radio access network, and a core network 14.
  • a 3GPP-type cellular network that may support standards such as LTE and/or NR (5G)
  • LTE and/or NR 5G
  • an access network 12 such as a radio access network
  • core network 14 such as a radio access network
  • the access network 12 comprises a plurality of network nodes 16a, 16b, 16c (referred to collectively as network nodes 16), such as NBs, eNBs, gNBs or other types of wireless access points, each defining a corresponding coverage area 18a, 18b, 18c (referred to collectively as coverage areas 18).
  • Each network node 16a, 16b, 16c is connectable to the core network 14 over a wired or wireless connection 20.
  • a first wireless device (WD) 22a located in coverage area 18a is configured to wirelessly connect to, or be paged by, the corresponding network node 16a.
  • a second WD 22b in coverage area 18b is wirelessly connectable to the corresponding network node 16b.
  • a plurality of WDs 22a, 22b are illustrated in this example, the disclosed embodiments are equally applicable to a situation where a sole WD is in the coverage area or where a sole WD is connecting to the corresponding network node 16.
  • the communication system may include many more WDs 22 and network nodes 16.
  • a WD 22 can be in simultaneous communication and/or configured to separately communicate with more than one network node 16 and more than one type of network node 16.
  • a WD 22 can have dual connectivity with a network node 16 that supports LTE and the same or a different network node 16 that supports NR.
  • WD 22 can be in communication with an eNB for LTE/E-UTRAN and a gNB for NR/NG-RAN.
  • the communication system 10 may itself be connected to a host computer 24, which may be embodied in the hardware and/or software of a standalone server, a cloud- implemented server, a distributed server or as processing resources in a server farm.
  • the host computer 24 may be under the ownership or control of a service provider, or may be operated by the service provider or on behalf of the service provider.
  • the connections 26, 28 between the communication system 10 and the host computer 24 may extend directly from the core network 14 to the host computer 24 or may extend via an optional intermediate network 30.
  • the intermediate network 30 may be one of, or a combination of more than one of, a public, private or hosted network.
  • the intermediate network 30, if any, may be a backbone network or the Internet. In some embodiments, the intermediate network 30 may comprise two or more sub-networks (not shown).
  • the communication system of FIG.4 as a whole enables connectivity between one of the connected WDs 22a, 22b and the host computer 24.
  • the connectivity may be described as an over-the-top (OTT) connection.
  • the host computer 24 and the connected WDs 22a, 22b are configured to communicate data and/or signaling via the OTT connection, using the access network 12, the core network 14, any intermediate network 30 and possible further infrastructure (not shown) as intermediaries.
  • the OTT connection may be transparent in the sense that at least some of the participating communication devices through which the OTT connection passes are unaware of routing of uplink and downlink communications.
  • a network node 16 may not or need not be informed about the past routing of an incoming downlink communication with data originating from a host computer 24 to be forwarded (e.g., handed over) to a connected WD 22a. Similarly, the network node 16 need not be aware of the future routing of an outgoing uplink communication originating from the WD 22a towards the host computer 24.
  • a network node 16 is configured to include a selection unit 32 which is configured to perform one or more functions described herein such as, for example, with respect to reciprocity-based precoding schemes.
  • a wireless device 22 is configured to include a TDCP unit 34 which is configured to perform one or more functions as described herein such as with respect to, for example, reciprocity-based precoding schemes.
  • a host computer 24 comprises hardware (HW) 38 including a communication interface 40 configured to set up and maintain a wired or wireless connection with an interface of a different communication device of the communication system 10.
  • the host computer 24 further comprises processing circuitry 42, which may have storage and/or processing capabilities.
  • the processing circuitry 42 may include a processor 44 and memory 46.
  • the processing circuitry 42 may comprise integrated circuitry for processing and/or control, e.g., one or more processors and/or processor cores and/or FPGAs (Field Programmable Gate Array) and/or ASICs (Application Specific Integrated Circuitry) adapted to execute instructions.
  • processors and/or processor cores and/or FPGAs Field Programmable Gate Array
  • ASICs Application Specific Integrated Circuitry
  • the processor 44 may be configured to access (e.g., write to and/or read from) memory 46, which may comprise any kind of volatile and/or nonvolatile memory, e.g., cache and/or buffer memory and/or RAM (Random Access Memory) and/or ROM (Read-Only Memory) and/or optical memory and/or EPROM (Erasable Programmable Read-Only Memory).
  • memory 46 may comprise any kind of volatile and/or nonvolatile memory, e.g., cache and/or buffer memory and/or RAM (Random Access Memory) and/or ROM (Read-Only Memory) and/or optical memory and/or EPROM (Erasable Programmable Read-Only Memory).
  • Processing circuitry 42 may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by host computer 24.
  • Processor 44 corresponds to one or more processors 44 for performing host computer 24 functions described herein.
  • the host computer 24 includes memory 46 that is configured to store data, programmatic software code and/or other information described herein.
  • the software 48 and/or the host application 50 may include instructions that, when executed by the processor 44 and/or processing circuitry 42, causes the processor 44 and/or processing circuitry 42 to perform the processes described herein with respect to host computer 24.
  • the instructions may be software associated with the host computer 24.
  • the software 48 may be executable by the processing circuitry 42.
  • the software 48 includes a host application 50.
  • the host application 50 may be operable to provide a service to a remote user, such as a WD 22 connecting via an OTT connection 52 terminating at the WD 22 and the host computer 24.
  • the host application 50 may provide user data which is transmitted using the OTT connection 52.
  • the “user data” may be data and information described herein as implementing the described functionality.
  • the host computer 24 may be configured for providing control and functionality to a service provider and may be operated by the service provider or on behalf of the service provider.
  • the processing circuitry 42 of the host computer 24 may enable the host computer 24 to observe, monitor, control, transmit to and/or receive from the network node 16 and or the wireless device 22.
  • the processing circuitry 42 of the host computer 24 may include an information unit 54 configured to enable the service provider to one or more of transmit, receive, communication, forward, relay, determine, analyze, store, process, etc. information related to reciprocity-based precoding schemes.
  • the communication system 10 further includes a network node 16 provided in a communication system 10 and including hardware 58 enabling it to communicate with the host computer 24 and with the WD 22.
  • the hardware 58 may include a communication interface 60 for setting up and maintaining a wired or wireless connection with an interface of a different communication device of the communication system 10, as well as a radio interface 62 for setting up and maintaining at least a wireless connection 64 with a WD 22 located in a coverage area 18 served by the network node 16.
  • the radio interface 62 may be formed as or may include, for example, one or more RF transmitters, one or more RF receivers, and/or one or more RF transceivers.
  • the communication interface 60 may be configured to facilitate a connection 66 to the host computer 24.
  • the connection 66 may be direct or it may pass through a core network 14 of the communication system 10 and/or through one or more intermediate networks 30 outside the communication system 10.
  • the hardware 58 of the network node 16 further includes processing circuitry 68.
  • the processing circuitry 68 may include a processor 70 and a memory 72.
  • the processing circuitry 68 may comprise integrated circuitry for processing and/or control, e.g., one or more processors and/or processor cores and/or FPGAs (Field Programmable Gate Array) and/or ASICs (Application Specific Integrated Circuitry) adapted to execute instructions.
  • the processing circuitry 68 may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by network node 16.
  • Processor 70 corresponds to one or more processors 70 for performing network node 16 functions described herein.
  • the memory 72 is configured to store data, programmatic software code and/or other information described herein.
  • the software 74 may include instructions that, when executed by the processor 70 and/or processing circuitry 68, causes the processor 70 and/or processing circuitry 68 to perform the processes described herein with respect to network node 16.
  • processing circuitry 68 of the network node 16 may include selection unit 32 configured to perform one or more functions as described herein such as with respect to, for example, reciprocity-based precoding schemes.
  • the communication system 10 further includes the WD 22 already referred to.
  • the WD 22 may have hardware 80 that may include a radio interface 82 configured to set up and maintain a wireless connection 64 with a network node 16 serving a coverage area 18 in which the WD 22 is currently located.
  • the radio interface 82 may be formed as or may include, for example, one or more RF transmitters, one or more RF receivers, and/or one or more RF transceivers.
  • the hardware 80 of the WD 22 further includes processing circuitry 84.
  • the processing circuitry 84 may include a processor 86 and memory 88.
  • the processor 86 may be configured to access (e.g., write to and/or read from) memory 88, which may comprise any kind of volatile and/or nonvolatile memory, e.g., cache and/or buffer memory and/or RAM (Random Access Memory) and/or ROM (Read-Only Memory) and/or optical memory and/or EPROM (Erasable Programmable Read-Only Memory).
  • memory 88 may comprise any kind of volatile and/or nonvolatile memory, e.g., cache and/or buffer memory and/or RAM (Random Access Memory) and/or ROM (Read-Only Memory) and/or optical memory and/or EPROM (Erasable Programmable Read-Only Memory).
  • the WD 22 may further comprise software 90, which is stored in, for example, memory 88 at the WD 22, or stored in external memory (e.g., database, storage array, network storage device, etc.) accessible by the WD 22.
  • the software 90 may be executable by the processing circuitry 84.
  • the client application 92 may be operable to provide a service to a human or non-human user via the WD 22, with the support of the host computer 24.
  • an executing host application 50 may communicate with the executing client application 92 via the OTT connection 52 terminating at the WD 22 and the host computer 24.
  • the client application 92 may receive request data from the host application 50 and provide user data in response to the request data.
  • the OTT connection 52 may transfer both the request data and the user data.
  • the client application 92 may interact with the user to generate the user data that it provides.
  • the processing circuitry 84 may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by WD 22.
  • the processor 86 corresponds to one or more processors 86 for performing WD 22 functions described herein.
  • the WD 22 includes memory 88 that is configured to store data, programmatic software code and/or other information described herein.
  • the software 90 and/or the client application 92 may include instructions that, when executed by the processor 86 and/or processing circuitry 84, causes the processor 86 and/or processing circuitry 84 to perform the processes described herein with respect to WD 22.
  • the processing circuitry 84 of the wireless device 22 may include a TDCP unit 34 configured to perform one or more functions as described herien such as with respect to, for example, reciprocity-based precoding schemes.
  • the inner workings of the network node 16, WD 22, and host computer 24 may be as shown in FIG.5 and independently, the surrounding network topology may be that of FIG.4.
  • the OTT connection 52 has been drawn abstractly to illustrate the communication between the host computer 24 and the wireless device 22 via the network node 16, without explicit reference to any intermediary devices and the precise routing of messages via these devices.
  • Network infrastructure may determine the routing, which it may be configured to hide from the WD 22 or from the service provider operating the host computer 24, or both.
  • the network infrastructure may further take decisions by which it dynamically changes the routing (e.g., on the basis of load balancing consideration or reconfiguration of the network).
  • the wireless connection 64 between the WD 22 and the network node 16 is in accordance with the teachings of the embodiments described throughout this disclosure.
  • One or more of the various embodiments improve the performance of OTT services provided to the WD 22 using the OTT connection 52, in which the wireless connection 64 may form the last segment. More precisely, the teachings of some of these embodiments may improve the data rate, latency, and/or power consumption and thereby provide benefits such as reduced user waiting time, relaxed restriction on file size, better responsiveness, extended battery lifetime, etc.
  • a measurement procedure may be provided for the purpose of monitoring data rate, latency and other factors on which the one or more embodiments improve.
  • the measurement procedure and/or the network functionality for reconfiguring the OTT connection 52 may be implemented in the software 48 of the host computer 24 or in the software 90 of the WD 22, or both.
  • sensors (not shown) may be deployed in or in association with communication devices through which the OTT connection 52 passes; the sensors may participate in the measurement procedure by supplying values of the monitored quantities exemplified above, or supplying values of other physical quantities from which software 48, 90 may compute or estimate the monitored quantities.
  • the reconfiguring of the OTT connection 52 may include message format, retransmission settings, preferred routing etc.; the reconfiguring need not affect the network node 16, and it may be unknown or imperceptible to the network node 16. Some such procedures and functionalities may be known and practiced in the art.
  • measurements may involve proprietary WD signaling facilitating the host computer’s 24 measurements of throughput, propagation times, latency and the like.
  • the measurements may be implemented in that the software 48, 90 causes messages to be transmitted, in particular empty or ‘dummy’ messages, using the OTT connection 52 while it monitors propagation times, errors, etc.
  • the host computer 24 includes processing circuitry 42 configured to provide user data and a communication interface 40 that is configured to forward the user data to a cellular network for transmission to the WD 22.
  • the cellular network also includes the network node 16 with a radio interface 62.
  • the network node 16 is configured to, and/or the network node’s 16 processing circuitry 68 is configured to perform the functions and/or methods described herein for preparing/initiating/maintaining/supporting/ending a transmission to the WD 22, and/or preparing/terminating/maintaining/supporting/ending in receipt of a transmission from the WD 22.
  • the host computer 24 includes processing circuitry 42 and a communication interface 40 that is configured to a communication interface 40 configured to receive user data originating from a transmission from a WD 22 to a network node 16.
  • the WD 22 is configured to, and/or comprises a radio interface 82 and/or processing circuitry 84 configured to perform the functions and/or methods described herein for preparing/initiating/maintaining/supporting/ending a transmission to the network node 16, and/or preparing/terminating/maintaining/supporting/ending in receipt of a transmission from the network node 16.
  • FIGS.4 and 5 show various “units” such as selection unit 32, and TDCP unit 34 as being within a respective processor, it is contemplated that these units may be implemented such that a portion of the unit is stored in a corresponding memory within the processing circuitry. In other words, the units may be implemented in hardware or in a combination of hardware and software within the processing circuitry.
  • FIG.6 is a flowchart illustrating an exemplary method implemented in a communication system, such as, for example, the communication system of FIGS.4 and 5, in accordance with one embodiment.
  • the communication system may include a host computer 24, a network node 16 and a WD 22, which may be those described with reference to FIG.5.
  • the host computer 24 provides user data (Block S100).
  • the host computer 24 provides the user data by executing a host application, such as, for example, the host application 50 (Block S102).
  • a host application such as, for example, the host application 50
  • the host computer 24 initiates a transmission carrying the user data to the WD 22 (Block S104).
  • the network node 16 transmits to the WD 22 the user data which was carried in the transmission that the host computer 24 initiated, in accordance with the teachings of the embodiments described throughout this disclosure (Block S106).
  • the WD 22 executes a client application, such as, for example, the client application 92, associated with the host application 50 executed by the host computer 24 (Block S108).
  • FIG.7 is a flowchart illustrating an exemplary method implemented in a communication system, such as, for example, the communication system of FIG.4, in accordance with one embodiment.
  • the communication system may include a host computer 24, a network node 16 and a WD 22, which may be those described with reference to FIGS.4 and 5.
  • the host computer 24 provides user data (Block S110).
  • the host computer 24 provides the user data by executing a host application, such as, for example, the host application 50.
  • the host computer 24 initiates a transmission carrying the user data to the WD 22 (Block S112).
  • the transmission may pass via the network node 16, in accordance with the teachings of the embodiments described throughout this disclosure.
  • FIG.8 is a flowchart illustrating an exemplary method implemented in a communication system, such as, for example, the communication system of FIG.4, in accordance with one embodiment.
  • the communication system may include a host computer 24, a network node 16 and a WD 22, which may be those described with reference to FIGS.4 and 5.
  • the WD 22 receives input data provided by the host computer 24 (Block S116).
  • the WD 22 executes the client application 92, which provides the user data in reaction to the received input data provided by the host computer 24 (Block S118).
  • the WD 22 provides user data (Block S120).
  • the WD provides the user data by executing a client application, such as, for example, client application 92 (Block S122).
  • the executed client application 92 may further consider user input received from the user.
  • the WD 22 may initiate, in an optional third substep, transmission of the user data to the host computer 24 (Block S124).
  • the host computer 24 receives the user data transmitted from the WD 22, in accordance with the teachings of the embodiments described throughout this disclosure (Block S126).
  • FIG.9 is a flowchart illustrating an exemplary method implemented in a communication system, such as, for example, the communication system of FIG.4, in accordance with one embodiment.
  • the communication system may include a host computer 24, a network node 16 and a WD 22, which may be those described with reference to FIGS.4 and 5.
  • the network node 16 receives user data from the WD 22 (Block S128).
  • the network node 16 initiates transmission of the received user data to the host computer 24 (Block S130).
  • the host computer 24 receives the user data carried in the transmission initiated by the network node 16 (Block S132).
  • FIG.10 is a flowchart of an exemplary process in a network node 16 according to one or more embodiments of the present disclosure.
  • One or more blocks described herein may be performed by one or more elements of network node 16 such as by one or more of processing circuitry 68 (including the selection unit 32), processor 70, radio interface 62 and/or communication interface 60.
  • Network node 16 is configured to select (Block S134) a reciprocity precoding scheme based on information related to a degree of time-variation of a channel, the information being associated with the wireless device 22, as described herein.
  • the information related to the degree of time-variation of the channel is included in time-domain channel property, TDCP, feedback from the wireless device 22.
  • the information related to the degree of time-variation of the channel comprises an amplitude of a normalized autocorrelation.
  • the selection of the reciprocity precoding scheme is based on the reciprocity precoding scheme being robust to channel variations.
  • the selection of the reciprocity precoding scheme is based on the reciprocity precoding scheme being robust to channel variations.
  • the selection of the reciprocity precoding scheme is based on the reciprocity precoding scheme being robust to channel variations.
  • the reciprocity precoding scheme that is selected is a grid of beams, GoB, based scheme where a spatial stream towards the wireless device 22 is restricted to a single beam selected from a codebook of spatial beams.
  • the processing circuitry 68 is further configured to at least one of: schedule the wireless device 22 for a single-user multiple- input multiple-output, SU-MIMO, transmission based on the amplitude of the normalized autocorrelation being below a threshold; and schedule the wireless device 22 for a multi- user MIMO, MU-MIMO, transmission based on the amplitude of the normalized autocorrelation being above a threshold;
  • the processing circuitry 68 is further configured to perform channel prediction corresponding to a future slot based on uplink channels measured across different sounding reference signals, SRSs, instances transmitted by the wireless device 22 based on the amplitude of the normalized autocorrelation being below a threshold.
  • the processing circuitry 68 is further configured to use a regularized precoder based on reciprocity, a regularization factor associated with the regularized precoder being based on the amplitude of the normalized autocorrelation.
  • the regularization factor is inversely proportional to the amplitude of the normalized autocorrelation.
  • the processing circuitry 68 is further configured to perform downlink transmission based on the selected reciprocity precoding scheme.
  • FIG.11 is a flowchart of an exemplary process in a wireless device 22 according to some embodiments of the present disclosure.
  • Wireless device 22 is configured to determine (Block S136) information related to a degree of time-variation of a channel associated with the wireless device 22, as described herein. Wireless device 22is configured to transmit (Block S138) the information to the network node 16, as described herein. Wireless device is configured to receive (Block S140) a downlink transmission according to a reciprocity precoding scheme that is selected based on the information, as described herein.
  • the information related to the degree of time-variation of the channel is included in time-domain channel property, TDCP, feedback from the wireless device 22.
  • the information related to the degree of time-variation of the channel comprises an amplitude of a normalized autocorrelation.
  • the amplitude of the normalized autocorrelation is less than a predefined threshold, the reciprocity precoding scheme that is used for the downlink transmission being robust to channel variations.
  • the precoders selected by network node 16 are transparent to wireless device 22.
  • the reciprocity precoding scheme that is used for the downlink transmission being robust to channel variations.
  • the amplitude of the normalized autocorrelation is less than a first predefined threshold and a signal to noise ratio, SNR, of a received sounding reference signal, SRS, is less than a second predefined threshold, the reciprocity precoding scheme that is used for the downlink transmission being robust to channel variations.
  • the reciprocity precoding scheme is based on a grid of beams, GoB, based scheme where a spatial stream towards the wireless device 22 is restricted to a single beam selected from a codebook of spatial beams.
  • the processing circuitry 84 is further configured to receive an indication of at least one of: a scheduling of the wireless device 22 for a single-user multiple-input multiple-output, SU-MIMO, transmission based on the amplitude of the normalized autocorrelation being below a threshold; and a scheduling of the wireless device 22 for a multi-user MIMO, MU-MIMO, transmission based on the amplitude of the normalized autocorrelation being above a threshold.
  • the sections below provide details and examples of arrangements for selection of one or more reciprocity-based precoding schemes. Some embodiments provide selection of one or more reciprocity-based precoding schemes.
  • the amplitude of the normalized autocorrelation reported in the TDCP feedback is used by network node 16 (e.g., gNB, TRP, scheduler, etc.) to switch between different types of reciprocity precoding schemes.
  • a reciprocity precoding scheme that is robust to channel variations is selected for the wireless device by network node 16 (e.g., gNB, TRP, scheduler, etc.).
  • a reciprocity precoding scheme that is robust to channel variations is selected by network node 16 (e.g., gNB, TRP, scheduler, etc.).
  • a reciprocity precoding scheme that is robust to channel variations is selected by network node 16 (e.g., gNB, TRP, scheduler, etc.).
  • network node 16 e.g., gNB, TRP, scheduler, etc.
  • An example of a reciprocity precoding scheme that is robust to channel variations is a simplified grid of beams (GoB) based scheme, where a spatial stream towards wireless device 22 is restricted to a single beam selected from a codebook of spatial beams.
  • a codebook of beamforming vectors is composed of DFT vectors.
  • the number of spatial streams or the rank selected for wireless device is restricted to a rank r by network node 16 (e.g., gNB, TRP, scheduler, etc.) when the amplitude of the normalized autocorrelation corresponding to a configured autocorrelation delay reported in the TDCP feedback is below a certain threshold.
  • wireless device 22 is scheduled for a single-user MIMO transmission by network node 16 (e.g., gNB, TRP, scheduler, etc.) when the amplitude of the normalized autocorrelation corresponding to a configured autocorrelation delay reported in the TDCP feedback is below a certain threshold.
  • the wireless device 22 when the amplitude of the normalized autocorrelation corresponding to a configured autocorrelation delay reported in the TDCP feedback is above a threshold, the wireless device 22 is scheduled by network node 16 (e.g., gNB, TRP, scheduler, etc.) for a multi-user MIMO transmission. In one or more embodiments, when the amplitude of the normalized autocorrelation corresponding to a configured autocorrelation delay reported in the TDCP feedback is below a threshold, network node 16 (e.g., gNB, TRP, scheduler, etc.) may perform combining of the uplink channels measured across different SRS instances transmitted by the wireless device 22 to improve channel estimation.
  • network node 16 e.g., gNB, TRP, scheduler, etc.
  • An example of combining is to average the channel measured at different time instances.
  • the combined channel is then used to compute the precoder for at least one of the following: ⁇ to schedule wireless device 22 for a multi-user MIMO transmission; and ⁇ to compute a MU-MIMO precoder using channel reciprocity.
  • a precoder is calculated using the transmitter side channel correlation matrix that captures the second order statistics of the channel which vary slowly over time is used by network node 16 (e.g., gNB, TRP, scheduler, etc.).
  • network node 16 when the amplitude of the normalized autocorrelation corresponding to a configured autocorrelation delay reported in the TDCP feedback is below a threshold, network node 16 (e.g., gNB, TRP, scheduler, etc.) may enable channel prediction corresponding to a future slot based on uplink channels measured across different SRS instances transmitted by the wireless device 22. The predicted channel is then used to compute the precoder for at least one of the following: • to schedule wireless device 22 for a single-user MIMO transmission, • to compute a reciprocity precoder scheme that is robust to channel variations according to the above embodiments.
  • a regularized precoder based on reciprocity is used by network node 16 (e.g., gNB, TRP, scheduler, etc.), where the regularization factor is determined based on the amplitude of the normalized autocorrelation, corresponding to a configured autocorrelation delay, reported in the TDCP feedback.
  • network node 16 e.g., gNB, TRP, scheduler, etc.
  • the regularization factor is determined based on the amplitude of the normalized autocorrelation, corresponding to a configured autocorrelation delay, reported in the TDCP feedback.
  • Examples of a regularized precoder are regularized zero-forcing, signal-to-leakage-and-noise ratio (SLNR), and minimum mean square error (MMSE) precoders.
  • the regularization factor is inversely proportional to the amplitude of the normalized autocorrelation.
  • Example 1 Example 1.
  • one or more embodiments and/or examples described herein provide one or more of the following advantages.
  • the solutions described herein make reciprocity-based precoding adaptive to how fast the MIMO channel varies in time. This advantageously makes the precoding more robust to time variations of the MIMO channel while utilizing richer (e.g., more and/or better) channel information for slowly varying channels. This will maximize throughput for both moving and stationary wireless devices and increase the network capacity.
  • Some embodiments may include one or more of the following: Embodiment A1.
  • a network node configured to communicate with a wireless device, the network node configured to, and/or comprising a radio interface and/or comprising processing circuitry configured to: select a reciprocity precoding scheme based on information related to a degree of time-variation of a channel, the information being associated with the wireless device.
  • Embodiment A2 The network node of Embodiment A1, wherein the information related to the degree of time-variation of the channel is included in time- domain channel property, TDCP, feedback from the wireless device.
  • Embodiment A3 The network node of any one of Embodiments A1-A2, wherein the information related to the degree of time-variation of the channel comprises an amplitude of a normalized autocorrelation.
  • Embodiment A3 wherein, if the amplitude of the normalized autocorrelation is less than a predefined threshold, the selection of the reciprocity precoding scheme is based on the reciprocity precoding scheme being robust to channel variations.
  • Embodiment A5. The network node of Embodiment A3, wherein, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a sounding reference signal, SRS, periodicity is greater than a second predefined threshold, the selection of the reciprocity precoding scheme is based on the reciprocity precoding scheme being robust to channel variations.
  • Embodiment A6 Embodiment A6.
  • Embodiment A3 wherein, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a signal to noise ratio, SNR, of a received sounding reference signal, SRS, is less than a second predefined threshold, the selection of the reciprocity precoding scheme is based on the reciprocity precoding scheme being robust to channel variations.
  • Embodiment A7 The network node of any one of Embodiments A1-A6, wherein the reciprocity precoding scheme that is selected is a grid of beams, GoB, based scheme where a spatial stream towards the wireless device is restricted to a single beam selected from a codebook of spatial beams.
  • Embodiment A8 Embodiment A8.
  • Embodiment A10 The network node of Embodiment A3, wherein the processing circuitry is further configured to use a regularized precoder based on reciprocity, a regularization factor associated with the regularized precoder being based on the amplitude of the normalized autocorrelation.
  • Embodiment A11 The network node of Embodiment A10, wherein the regularization factor is inversely proportional to the amplitude of the normalized autocorrelation.
  • Embodiment A12 The network node of any one of Embodiments A1-A11, wherein the processing circuitry is further configured to perform downlink transmission based on the selected reciprocity precoding scheme.
  • Embodiment B1. A method implemented by a network node that is configured to communicate with a wireless device, the method comprising: selecting a reciprocity precoding scheme based on information related to a degree of time-variation of a channel, the information being associated with the wireless device.
  • Embodiment B2. The method of Embodiment B1, wherein the information related to the degree of time-variation of the channel is included in time-domain channel property, TDCP, feedback from the wireless device.
  • Embodiment B4 The method of any one of Embodiments B1-B2, wherein the information related to the degree of time-variation of the channel comprises an amplitude of a normalized autocorrelation.
  • Embodiment B4 The method of Embodiment B3, wherein, if the amplitude of the normalized autocorrelation is less than a predefined threshold, the selection of the reciprocity precoding scheme is based on the reciprocity precoding scheme being robust to channel variations.
  • Embodiment B3 wherein, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a sounding reference signal, SRS, periodicity is greater than a second predefined threshold, the selection of the reciprocity precoding scheme is based on the reciprocity precoding scheme being robust to channel variations.
  • Embodiment B6 The method of Embodiment B3, wherein, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a signal to noise ratio, SNR, of a received sounding reference signal, SRS, is less than a second predefined threshold, the selection of the reciprocity precoding scheme is based on the reciprocity precoding scheme being robust to channel variations.
  • Embodiment B7 Embodiment B7.
  • Embodiment B8 The method of any one of Embodiments B1-B6, wherein the reciprocity precoding scheme that is selected is a grid of beams, GoB, based scheme where a spatial stream towards the wireless device is restricted to a single beam selected from a codebook of spatial beams.
  • Embodiment B8 The method of Embodiment B3, further comprising at least one of: scheduling the wireless device for a single-user multiple-input multiple-output, SU-MIMO, transmission based on the amplitude of the normalized autocorrelation being below a threshold; and scheduling the wireless device for a multi-user MIMO, MU-MIMO, transmission based on the amplitude of the normalized autocorrelation being above a threshold; Embodiment B9.
  • Embodiment B3 further comprising performing channel prediction corresponding to a future slot based on uplink channels measured across different sounding reference signals, SRSs, instances transmitted by the wireless device based on the amplitude of the normalized autocorrelation being below a threshold.
  • Embodiment B10 The method of Embodiment B3, further comprising using a regularized precoder based on reciprocity, a regularization factor associated with the regularized precoder being based on the amplitude of the normalized autocorrelation.
  • Embodiment B11 The method of Embodiment B10, wherein the regularization factor is inversely proportional to the amplitude of the normalized autocorrelation.
  • Embodiment C1 A wireless device configured to communicate with a network node, the wireless device configured to, and/or comprising a radio interface and/or processing circuitry configured to: determine information related to a degree of time-variation of a channel associated with the wireless device; transmit the information to the network node; and receive a downlink transmission according to a reciprocity precoding scheme that is selected based on the information.
  • Embodiment C2. The wireless device of Embodiment C1, wherein the information related to the degree of time-variation of the channel is included in time- domain channel property, TDCP, feedback from the wireless device.
  • Embodiment C4 The wireless device of Embodiment C3, wherein, if the amplitude of the normalized autocorrelation is less than a predefined threshold, the reciprocity precoding scheme that is used for the downlink transmission being robust to channel variations.
  • Embodiment C3 wherein, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a sounding reference signal, SRS, periodicity is greater than a second predefined threshold, the reciprocity precoding scheme that is used for the downlink transmission being robust to channel variations.
  • Embodiment C6 The wireless device of Embodiment C3, wherein, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a signal to noise ratio, SNR, of a received sounding reference signal, SRS, is less than a second predefined threshold, the reciprocity precoding scheme that is used for the downlink transmission being robust to channel variations.
  • Embodiment C7 Embodiment C7.
  • Embodiment D1 A method implemented by a wireless device that is configured to communicate with a network node, the method comprising: determining information related to a degree of time-variation of a channel associated with the wireless device; transmitting the information to the network node; and receiving a downlink transmission according to a reciprocity precoding scheme that is selected based on the information.
  • Embodiment D1 wherein the information related to the degree of time-variation of the channel is included in time-domain channel property, TDCP, feedback from the wireless device.
  • Embodiment D3. The method of any one of Embodiments D1-D2, wherein the information related to the degree of time-variation of the channel comprises an amplitude of a normalized autocorrelation.
  • Embodiment D4. The method of Embodiment D3, wherein, if the amplitude of the normalized autocorrelation is less than a predefined threshold, the reciprocity precoding scheme that is used for the downlink transmission being robust to channel variations.
  • Embodiment D3 wherein, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a sounding reference signal, SRS, periodicity is greater than a second predefined threshold, the reciprocity precoding scheme that is used for the downlink transmission being robust to channel variations.
  • Embodiment D6 The method of Embodiment D3, wherein, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a signal to noise ratio, SNR, of a received sounding reference signal, SRS, is less than a second predefined threshold, the reciprocity precoding scheme that is used for the downlink transmission being robust to channel variations.
  • Embodiment D7 Embodiment D7.
  • Embodiment D8 The method of any one of Embodiments D1-D6, wherein the reciprocity precoding scheme is based on a grid of beams, GoB, based scheme where a spatial stream towards the wireless device is restricted to a single beam selected from a codebook of spatial beams.
  • Embodiment D8 The method of Embodiment D3, further comprising receiving at least one of: a scheduling of the wireless device for a single-user multiple-input multiple-output, SU-MIMO, transmission based on the amplitude of the normalized autocorrelation being below a threshold; and a scheduling of the wireless device for a multi-user MIMO, MU-MIMO, transmission based on the amplitude of the normalized autocorrelation being above a threshold.
  • the concepts described herein may be embodied as a method, data processing system, computer program product and/or computer storage media storing an executable computer program. Accordingly, the concepts described herein may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects all generally referred to herein as a “circuit” or “module.” Any process, step, action and/or functionality described herein may be performed by, and/or associated to, a corresponding module, which may be implemented in software and/or firmware and/or hardware. Furthermore, the disclosure may take the form of a computer program product on a tangible computer usable storage medium having computer program code embodied in the medium that can be executed by a computer.
  • Any suitable tangible computer readable medium may be utilized including hard disks, CD-ROMs, electronic storage devices, optical storage devices, or magnetic storage devices.
  • These computer program instructions may be provided to a processor of a general purpose computer (to thereby create a special purpose computer), special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.
  • These computer program instructions may also be stored in a computer readable memory or storage medium that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer readable memory produce an article of manufacture including instruction means which implement the function/act specified in the flowchart and/or block diagram block or blocks.
  • the computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. It is to be understood that the functions/acts noted in the blocks may occur out of the order noted in the operational illustrations. For example, two blocks shown in succession may in fact be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
  • Computer program code for carrying out operations of the concepts described herein may be written in an object oriented programming language such as Python, Java® or C++. However, the computer program code for carrying out operations of the disclosure may also be written in conventional procedural programming languages, such as the "C" programming language. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer.
  • the remote computer may be connected to the user's computer through a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider).
  • LAN local area network
  • WAN wide area network
  • Internet Service Provider an Internet Service Provider

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Abstract

A method, system and apparatus are disclosed. According to some embodiments, a network node is configured to select a reciprocity precoding scheme based on information related to a degree of time-variation of a channel, the information being associated with the wireless device.

Description

RECIPROCITY PRECODING SCHEME SELECTION USING TIME DOMAIN CHANNEL PROPERTIES (TDCP) FEEDBACK TECHNICAL FIELD The present disclosure relates to wireless communications, and in particular, to reciprocity-based precoding schemes. BACKGROUND The Third Generation Partnership Project (3GPP) has developed and is developing standards for Fourth Generation (4G) (also referred to as Long Term Evolution (LTE)) and Fifth Generation (5G) (also referred to as New Radio (NR)) wireless communication systems. Such systems provide, among other features, broadband communication between network nodes, such as base stations, and mobile user equipment (UE) or wireless devices (WD), as well as communication between network nodes and between UEs. The 3GPP is also developing standards for Sixth Generation (6G) wireless communication networks. In particular, the 5G mobile wireless communication system or NR, supports a diverse set of use cases and a diverse set of deployment scenarios. The later includes deployment at both low frequencies (100s of MHz), and very high frequencies (mm waves in the tens of GHz). NR uses OFDM (Orthogonal Frequency Division Multiplexing) in the downlink (i.e., from a network node, or gNB, to a user equipment (UE) or wireless device). It is also referred to as CP-OFDM (Cyclic Prefix OFDM). In the uplink (i.e., from wireless device to network node), both CP-OFDM and DFT-spread OFDM (DFT-S-OFDM) are supported. The basic NR physical resource is a time-frequency grid as illustrated in FIG.1, where each resource element corresponds to one OFDM subcarrier during one OFDM symbol interval. Although a subcarrier spacing of ∆ ^^ ൌ 15 ^^ ^^ ^^ is shown in FIG.1, different subcarrier spacing values are supported in NR. The supported subcarrier spacing values (also referred to as different numerologies) in NR are given by ∆ ^^ ൌ ^15 ൈ 2ఈ^ ^^ ^^ ^^ where ^^ is a non-negative integer. Furthermore, the resource allocation in NR may be described in terms of resource blocks, where a resource block corresponds to one slot (0.5 ms) in the time domain and 12 contiguous subcarriers in the frequency domain. Resource blocks are numbered in the frequency domain, starting with 0 from one end of the system bandwidth. Downlink transmissions are dynamically scheduled, i.e., in each slot the network node transmits downlink control information (DCI) about which wireless device data is to be transmitted to and which resource blocks in the current or a future the data is transmitted on. This control signaling is typically transmitted in the first one or two OFDM symbols in each slot in NR. The control information is carried on Physical Control Channel (PDCCH) and data is carried on Physical Downlink Shared Channel (PDSCH). A wireless device first detects and decodes PDCCH and if a PDCCH is decoded successfully, it the decodes the corresponding PDSCH based on the decoded control information in the PDCCH. Uplink data transmissions are also dynamically scheduled using PDCCH. Similar to downlink, a wireless device first decodes uplink grants in PDCCH and then transmits data over the Physical Uplink Shared Channel (PUSCH) based the decoded control information in the uplink grant such as modulation order, coding rate, uplink resource allocation, and etc. In addition to PUSCH, Physical Uplink Control Channel (PUCCH) is also supported in NR to carry uplink control information (UCI) such as HARQ (Hybrid Automatic Repeat Request) related Acknowledgement (ACK), Negative Acknowledgement (NACK), or Channel State Information (CSI) feedback. 2D antenna arrays Two-dimensional antenna arrays may be (partly) described by the number of antenna columns corresponding to the horizontal dimension ^^^ where the number of antenna rows correspond to the vertical dimension ^^௩ and the number of dimensions corresponds to different polarizations ^^^. The total number of antennas is thus ^^ ൌ ^^^ ^^௩ ^^^. The concept of an antenna is non-limiting in the sense that it can refer to any virtualization (e.g., linear mapping) of the physical antenna elements. For example, pairs of physical sub-elements could be fed the same signal, and hence share the same virtualized antenna port. An example of a 4x8 array with dual-polarized antenna elements is illustrated in FIG.2 where the two-dimensional antenna array has dual-polarized antenna elements (N^ ൌ 2 with +45 degree and -45 degree slant polarizations) with n୦ ൌ 8 and n^ ൌ 4. For ease of mathematical modeling and as a convention, the antenna element corresponding to the first polarization in the ^^-th row and ^^-th column is indexed by ^ ^^ െ 1^ ^^௩ ^ ^^, and the antenna element corresponding to the second polarization in the ^^-th row and ^^-th column is indexed by ^ ^^ െ 1 ^ ^^௩ ^ ^^ ^ ^^୦ ^^^. Precoding may be interpreted as multiplying the signal with different beamforming weights for each antenna prior to transmission. A typical approach is to tailor the precoder to the antenna form factor, i.e. taking into account ^^^, ^^௩, ^^^ and the separation between the antennas ^^୦, ^^^ when designing the precoder codebook. Precoding, of which beamforming is a special case, from an antenna array can be considered a matrix operation, where one or more input signals to be transmitted can be individually precoded. The precoding operation can be expressed as ^^ ൌ ^^ ^^
Figure imgf000004_0001
where the transmitted signals are represented as a set of ^^^ symbol streams or layers in ^^; ^^^is the signal transmitted on the ^^-th antenna element of the antenna array and ^^^,^ is a complex valued precoding weight corresponding to the ^^-th layer and the ^^-th antenna element. The ^^-th column of the precoding matrix ^^, ^^^, is the precoding vector corresponding to the ^^-th layer. FIG.3 is a diagram of an example of precoding. Under the antenna indexing convention described above, the elements 1 to ^^୦ ^^^ of each column of ^^ correspond to the first polarization, while the elements ^^୦ ^^^ ^ 1 to 2 ^^୦ ^^^ of each column of ^^ correspond to the second polarization. The precoding operation can also be expressed as
Figure imgf000004_0002
where ^^^^^ ^ is the polarization specific precoder vector containing the weights corresponding to the ^^-th layer and the antenna elements of the ^^-th polarization. Grid-of-Beams (GoB) precoding In grid-of-beams precoding, each symbol stream or layer is transmitted over one or more spatial beams selected from a set of predefined beams. In the model described above, this implies that ^^^^^ ^ , the precoding vector for the ^^-th layer and ^^-th polarization, is selected from a set of predefined vectors. DFT-based precoders A common type of grid-of-beams precoding is to use a DFT-precoder, where the precoder vector used to precode a single-layer transmission using a single-polarized uniform linear array (ULA) with N antennas is defined as where k ൌ 0,1, … ON െ 1 is the precoder index and O is an integer oversampling factor. u୩ is also referred to as an one dimension (1-D) DFT beam with beam index k. If ULA is along the horizontal dimension, each DFT beam points to an azimuth direction. If ULA is along the vertical dimension, each DFT beam points to an elevation direction. Each precoder corresponds to a DFT beam. A corresponding precoder vector for a two-dimensional uniform planar array (UPA) with N^ antenna ports in one dimension and Nଶ antenna ports in another dimension can be created by taking the Kronecker product of two precoder vectors as w ^2-D^^k, l^ ൌ v୩,୪ ൌ u୩,^ ^u୪,ଶ,
Figure imgf000005_0005
beams in each of the two dimensions, and
Figure imgf000005_0001
and Oଶ are the over sampling factors in two dimensions associated with N^ and Nଶ , respectively. v୩,୪ is also referred to a two dimension (2-D) DFT beam characterized by two beam indices ^k, l^, one in each dimension. Each precoder corresponds to a 2D DFT beam. Extending the DFT precoder for a dual-polarized UPA may then be performed as
Figure imgf000005_0002
where ^^^థ is a co-phasing factor that may be selected from M-PSK alphabet such
Figure imgf000005_0003
A precoder matrix ^^ for multi-layer transmission may be created by appending columns of DFT precoder vectors as
Figure imgf000005_0004
where ^^ is the number of transmission layers. Such DFT-based precoders are used for instance in NR Type I CSI feedback, where each layer is associated with 2D DFT beam. Downlink Transmission based on Channel Reciprocity In reciprocity-based downlink precoding, a network node measures the channel between a wireless device and itself using UL reference signals such as UL SRS, and the measured channel is used to determine a precoder for a downlink transmission under the assumption of channel reciprocity between uplink and downlink. In time division duplexing (TDD) systems, DL and UL channel is reciprocal. Comparing to CSI-RS based DL precoder matrix index (PMI) feedback, reciprocity-based precoding reduces the feedback overhead in UL and has a smaller delay between measurement of the channel and the application of the precoder. In reciprocity-based downlink precoding, a network node can schedule a wireless device with either single-user multi-input multi-output (SU-MIMO) or multi-user multi- input multi-output (MU-MIMO) transmission. In SU-MIMO, a set of DL time and frequency resources are used to transmit DL data to a single wireless device. In MU- MIMO, the same set of time and frequency resources are used to transmit data to a selected set of multiple users (e.g., wireless devices) using a MU-MIMO precoding scheme. In both, SU-MIMO and MU-MIMO transmission, a network node may need to select appropriate number of spatial streams for each wireless device to satisfy the per user requirement and maximize the system performance. One type of reciprocity-based precoding is the so called zero-forcing (ZF) precoder which aims to beamform to the desired wireless device while creating nulls to other co- scheduled wireless devices. Assuming a MU-MIMO case with ^^ co-scheduled wireless devices, each with a single antenna, and a network node with ^^ antenna elements, the ZF precoding matrix is given by ^^ ൌ ^^ ு^ ^^ ^^ ு^ି^ where ^^ is the ^^ ൈ ^^ channel matrix between the network node and the co- scheduled wireless devices. One problem with this approach is that there will be a significant gain reduction if any two wireless devices have similar channels. A way to mitigate this problem is to regularize the inverse by adding a multiple of the identity matrix before inverting, i.e., ^^ ൌ ^^ு^ ^^ ^^ு ^ ^^ ^^^ି^ where ^^ denotes the ^^ ൈ ^^ identity matrix and the regularization factor, ^^, is a real scalar. This precoder is sometimes referred to as a regularized ZF precoder. A particular choice of regularization factor is ^^ ൌ ^^ ^^ଶ/ ^^ where ^^ଶ is the receiver noise power and ^^ is the transmitted power. This solution is referred to as the minimum mean square error (MMSE) precoder. A related precoder is the signal-to-leakage-and-noise ratio (SLNR) precoder which, up to a proportionality constant, is given by
Figure imgf000007_0001
where ^^^ is the precoding vector to the k-th wireless device, ℒ is the set of all co- scheduled wireless devices, ^^^ is a right-singular vector of the channel matrix and ^^^ is the rresponding singular value. Here, ఒమ co ^ ఙ^ మ may be interpreted as regularization factor. Sounding Reference Signal (SRS) SRS is supported in NR for uplink channel sounding. Configurable SRS bandwidth is supported in NR. SRS can be configurable with regard to density in frequency domain (e.g., comb levels) and/or in time domain (including multi-symbol SRS transmissions). A wireless device can be configured with one or more SRS resource sets, each SRS resource set can contain one or more SRS resources. Each SRS resource can contain ^^a S pRS ∈ ^ 1,2,4 ^ SRS antenna ports in a time-frequency resource with
Figure imgf000007_0002
∈ ^ 1,2,4,8,10,12,14 ^ consecutive OFDM symbols in a slot starting from OFDM symbol ^^^ and a number PRBs starting from subcarrier ^^^. An SRS sequence for an SRS antenna port ^^^ at OFDM symbol ^^′ in an SRS resource is a cyclic shifted version of a Zadoff-Chu sequence ^^̄௨,௩^ ^^^ with a group numberu ^ ^0,1,...,29 ^ and a base sequence number ^^ ∈ ^0,1^ within the group, i.e.,
Figure imgf000007_0003
where ^^ZC ൌ
Figure imgf000007_0004
is the length of the sequence, ^^ is the number of RBs configured for the SRS resource, ^^s R cB ൌ 12 is the number sub-carriers per RB, ^^ ൌ log2 ^ ^^TC ^ and ^^TC ∈ ^ 2,4,8 ^ is a configured comb value where the SRS sequence occupies every ^^ ^cs,^ TC sub-carriers, ^^^ ൌ 2 ^^ SRS cs,max ^cs,max is a cyclic shift and ^^SRS is maximum SRS number of cyclic shifts that can be configured as shown and/or described in 3GPP standards such as in, for example, Table 6.4.1.4.2-1 (reproduced below) in 3GPP
Figure imgf000007_0005
Table 6.4.1.4.2-1: Maximum number of cyclic shifts ^^ୡ^,୫ୟ^ ୗୖୗ as a function of ^^TC. ^^ ୡ^,୫ୟ^ TC ^^ୗୖୗ 2 8 4 12 8 6 In case of two SRS ports contained in a SRS resource, the two SRS ports are mapped to the same comb offset but allocated with two different cyclic shifts separated by ^^. In case of four SRS ports contained in a SRS resource, two possible port-allocation options are supported (unless the transmission comb is 8 (supported since NR Rel-17) for which only the second option is supported). In a first option, the four SRS ports are mapped to the same comb offset but allocated four different cyclic shifts separated by ^^/2. In a second option, the first two SRS ports are allocated with two different cyclic shifts separated by ^^ on a same set of sub-carriers (with a same first comb offset) and the last two SRS ports are allocated with the same two different cyclic shifts as the first two SRS ports but on a different set of sub-carriers (with a same second comb offset). SRS can be configured by the network (e.g., network node) to be transmitted periodically, aperiodically on a trigger or in a semi-persistent manner. In the case of periodic and semi-persistent transmission the network can configure SRS transmission with a periodicity ^^ ∈ {1, 2, 4, 5, 8, 10, 16, 20, 32, 40, 64, 80, 160, 320, 640, 1280, 2560} slots. 3GPP Release 18 (Rel-18) Time domain channel property (TDCP) feedback In the Release 18 enhancements of 5G NR, a time-domain channel property (TDCP) feedback that indicates the degree of time-variability of the channel is being introduced. The channel autocorrelation is a direct measure of how fast the channel varies with time. The TDCP feedback report contains the amplitude of the normalized instantaneous autocorrelation function. For example, the normalized amplitude of the TDCP can be given as follows for an autocorrelation delay of ∆ ^^:
Figure imgf000008_0001
where ℎ^ ^ ^^^ is the channel for subcarrier ^^ at time ^^. For the normalization, in the denominator, the geometric average over the two time-instances ^^ and ^^ ^ ∆ ^^ of the zero- delay autocorrelation function is used in order to make the metric robust against automatic gain control (AGC). To get a metric that is robust also towards phase discontinuities e.g., due to frequency adjustments the absolute value of the instantaneous autocorrelation function is used and this quantity is referred to as the channel correlation amplitude. For a given delay ∆ ^^, the absolute value of the instantaneous autocorrelation function typically decreases with increase in channel time-variability. In TDD systems, reciprocity-based precoding schemes can be used instead of wireless device feedback based schemes for wireless devices with sufficient UL SNR. However, using a reciprocity-based scheme that is sensitive to time-variations of the channel between the wireless device and a network node degrades both the user and the system performance when channel varies. SUMMARY Some embodiments advantageously provide methods, systems, and apparatuses for reciprocity-based precoding schemes for wireless communications. According to one or more embodiments, the time-domain channel property (TDCP) feedback, from a wireless device, which contains information related to the degree of time-variation of the channel can be used to select the type of reciprocity-based precoding scheme used. According to one aspect, a method implemented by a network node that is configured to communicate with a wireless device, is provided. The method comprises selecting a reciprocity precoding scheme based on information related to a degree of time- variation of a channel, the information being associated with the wireless device. According to this aspect, in some embodiments, the information related to the degree of time-variation of the channel is included in time-domain channel property, TDCP, feedback from the wireless device. In some embodiments, the information related to the degree of time-variation of the channel comprises an amplitude of a normalized autocorrelation. In some embodiments, if the amplitude of the normalized autocorrelation is less than a predefined threshold, the selection of the reciprocity precoding scheme is based on the reciprocity precoding scheme being robust to channel variations. In some embodiments,, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a sounding reference signal, SRS, periodicity is greater than a second predefined threshold, the selection of the reciprocity precoding scheme is based on the reciprocity precoding scheme being robust to channel variations. In some embodiments, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a signal to noise ratio, SNR, of a received sounding reference signal, SRS, is less than a second predefined threshold, the selection of the reciprocity precoding scheme is based on the reciprocity precoding scheme being robust to channel variations. In some embodiments, the reciprocity precoding scheme that is selected is a grid of beams, GoB, based scheme where a spatial stream towards the wireless device is restricted to a single beam selected from a codebook of spatial beams. In some embodiments, the method further comprises at least one of scheduling the wireless device for a single-user multiple-input multiple-output, SU-MIMO, transmission based on the amplitude of the normalized autocorrelation being below a threshold, and scheduling the wireless device for a multi-user MIMO, MU-MIMO, transmission based on the amplitude of the normalized autocorrelation being above a threshold. In some embodiments, the method further comprises performing channel prediction corresponding to a future slot based on uplink channels measured across different sounding reference signals, SRSs, instances transmitted by the wireless device based on the amplitude of the normalized autocorrelation being below a threshold. In some embodiments, the method further comprises using a regularized precoder based on reciprocity, a regularization factor associated with the regularized precoder being based on the amplitude of the normalized autocorrelation. In some embodiments, the regularization factor is inversely proportional to the amplitude of the normalized autocorrelation. In some embodiments, the method further comprises performing downlink transmission based on the selected reciprocity precoding scheme. According to some aspects, a network node a network node configured to communicate with a wireless device, the network node configured to, and/or comprising a radio interface and/or comprising processing circuitry configured to perform any of the steps of above noted methods, is provided. According to some aspects, a method implemented by a wireless device that is configured to communicate with a network node, is provide. The method comprises determining information related to a degree of time-variation of a channel associated with the wireless device, transmitting the information to the network node and receiving a downlink transmission according to a reciprocity precoding scheme that is selected based on the information. According to these aspects, in some embodiments, the information related to the degree of time-variation of the channel is included in time-domain channel property, TDCP, feedback from the wireless device. In some embodiments, the information related to the degree of time-variation of the channel comprises an amplitude of a normalized autocorrelation. In some embodiments, if the amplitude of the normalized autocorrelation is less than a predefined threshold, the reciprocity precoding scheme that is used for the downlink transmission being robust to channel variations. In some embodiments, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a sounding reference signal, SRS, periodicity is greater than a second predefined threshold, the reciprocity precoding scheme that is used for the downlink transmission being robust to channel variations. In some embodiments, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a signal to noise ratio, SNR, of a received sounding reference signal, SRS, is less than a second predefined threshold, the reciprocity precoding scheme that is used for the downlink transmission being robust to channel variations. In some embodiments, the reciprocity precoding scheme is based on a grid of beams, GoB, based scheme where a spatial stream towards the wireless device is restricted to a single beam selected from a codebook of spatial beams. In some embodiments, the method further comprises receiving at least one of a scheduling of the wireless device for a single-user multiple-input multiple-output, SU-MIMO, transmission based on the amplitude of the normalized autocorrelation being below a threshold and a scheduling of the wireless device for a multi-user MIMO, MU-MIMO, transmission based on the amplitude of the normalized autocorrelation being above a threshold. According to some aspects, a wireless device configured to communicate with a network node, the wireless device configured to, and/or comprising a radio interface and/or processing circuitry configured to perform any of the above noted steps is provided. BRIEF DESCRIPTION OF THE DRAWINGS A more complete understanding of the present embodiments, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: FIG.1 is a diagram of an example of NR physical resources; FIG.2 is a diagram of an example of a two-dimensional antenna array of dual polarized antenna elements; FIG.3 is a diagram of an example of precoding; FIG.4 is a schematic diagram of an exemplary network architecture illustrating a communication system connected via an intermediate network to a host computer according to the principles in the present disclosure; FIG.5 is a block diagram of a host computer communicating via a network node with a wireless device over an at least partially wireless connection according to some embodiments of the present disclosure; FIG.6 is a flowchart illustrating exemplary methods implemented in a communication system including a host computer, a network node and a wireless device for executing a client application at a wireless device according to some embodiments of the present disclosure; FIG.7 is a flowchart illustrating exemplary methods implemented in a communication system including a host computer, a network node and a wireless device for receiving user data at a wireless device according to some embodiments of the present disclosure; FIG.8 is a flowchart illustrating exemplary methods implemented in a communication system including a host computer, a network node and a wireless device for receiving user data from the wireless device at a host computer according to some embodiments of the present disclosure; FIG.9 is a flowchart illustrating exemplary methods implemented in a communication system including a host computer, a network node and a wireless device for receiving user data at a host computer according to some embodiments of the present disclosure; FIG.10 is a flowchart of an exemplary process in a network node according to some embodiments of the present disclosure; and FIG.11 is a flowchart of an exemplary process in a wireless device according to some embodiments of the present disclosure. DETAILED DESCRIPTION As described above, in TDD systems, reciprocity-based precoding schemes can be used instead of wireless device feedback based schemes for wireless devices with sufficient UL SNR. However, using a reciprocity-based scheme that is sensitive to time- variations of the channel between the wireless device and a network node degrades both the user and the system performance when channel varies. Hence, how to mitigate such performance degradation in reciprocity based precoding schemes is an unsolved problem. One or more embodiments of the present disclosure solve at least in part this issues with reciprocity-based schemes by, for example, selecting the type of reciprocity-based precoding scheme to be used based on TDCP feedback, from the wireless device, where the TDCP feedback contains information related to the degree of time-variation of the channel. Before describing in detail example embodiments, it is noted that the embodiments reside primarily in combinations of apparatus components and processing steps related to reciprocity-based precoding schemes. Accordingly, components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. Like numbers refer to like elements throughout the description. As used herein, relational terms, such as “first” and “second,” “top” and “bottom,” and the like, may be used solely to distinguish one entity or element from another entity or element without necessarily requiring or implying any physical or logical relationship or order between such entities or elements. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the concepts described herein. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes” and/or “including” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. In embodiments described herein, the joining term, “in communication with” and the like, may be used to indicate electrical or data communication, which may be accomplished by physical contact, induction, electromagnetic radiation, radio signaling, infrared signaling or optical signaling, for example. One having ordinary skill in the art will appreciate that multiple components may interoperate and modifications and variations are possible of achieving the electrical and data communication. In some embodiments described herein, the term “coupled,” “connected,” and the like, may be used herein to indicate a connection, although not necessarily directly, and may include wired and/or wireless connections. The term “network node” used herein can be any kind of network node comprised in a radio network which may further comprise any of base station (BS), radio base station, base transceiver station (BTS), base station controller (BSC), radio network controller (RNC), g Node B (gNB), evolved Node B (eNB or eNodeB), Node B, multi- standard radio (MSR) radio node such as MSR BS, transmission reception point (TRP), scheduler, multi-cell/multicast coordination entity (MCE), integrated access and backhaul (IAB) node, relay node, donor node controlling relay, radio access point (AP), transmission points, transmission nodes, Remote Radio Unit (RRU) Remote Radio Head (RRH), a core network node (e.g., mobile management entity (MME), self-organizing network (SON) node, a coordinating node, positioning node, MDT node, etc.), an external node (e.g., 3rd party node, a node external to the current network), nodes in distributed antenna system (DAS), a spectrum access system (SAS) node, an element management system (EMS), etc. The network node may also comprise test equipment. The term “radio node” used herein may be used to also denote a wireless device (WD) such as a wireless device (WD) or a radio network node. In some embodiments, the non-limiting terms wireless device (WD) or a user equipment (UE) are used interchangeably. The WD herein can be any type of wireless device capable of communicating with a network node or another WD over radio signals, such as wireless device (WD). The WD may also be a radio communication device, target device, device to device (D2D) WD, machine type WD or WD capable of machine to machine communication (M2M), low-cost and/or low-complexity WD, a sensor equipped with WD, Tablet, mobile terminals, smart phone, laptop embedded equipped (LEE), laptop mounted equipment (LME), USB dongles, Customer Premises Equipment (CPE), an Internet of Things (IoT) device, or a Narrowband IoT (NB-IOT) device, etc. Also, in some embodiments the generic term “radio network node” is used. It can be any kind of a radio network node which may comprise any of base station, radio base station, base transceiver station, base station controller, network controller, RNC, evolved Node B (eNB), Node B, gNB, Multi-cell/multicast Coordination Entity (MCE), IAB node, relay node, access point, radio access point, Remote Radio Unit (RRU) Remote Radio Head (RRH). Note that although terminology from one particular wireless system, such as, for example, 3GPP LTE and/or New Radio (NR), may be used in this disclosure, this should not be seen as limiting the scope of the disclosure to only the aforementioned system. Other wireless systems, including without limitation Wide Band Code Division Multiple Access (WCDMA), Worldwide Interoperability for Microwave Access (WiMax), Ultra Mobile Broadband (UMB) and Global System for Mobile Communications (GSM), may also benefit from exploiting the ideas covered within this disclosure. Note further, that functions described herein as being performed by a wireless device or a network node may be distributed over a plurality of wireless devices and/or network nodes. In other words, it is contemplated that the functions of the network node and wireless device described herein are not limited to performance by a single physical device and, in fact, can be distributed among several physical devices. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. Some embodiments provide reciprocity-based precoding schemes. Referring now to the drawing figures, in which like elements are referred to by like reference numerals, there is shown in FIG.4 a schematic diagram of a communication system 10, according to an embodiment, such as a 3GPP-type cellular network that may support standards such as LTE and/or NR (5G), which comprises an access network 12, such as a radio access network, and a core network 14. The access network 12 comprises a plurality of network nodes 16a, 16b, 16c (referred to collectively as network nodes 16), such as NBs, eNBs, gNBs or other types of wireless access points, each defining a corresponding coverage area 18a, 18b, 18c (referred to collectively as coverage areas 18). Each network node 16a, 16b, 16c is connectable to the core network 14 over a wired or wireless connection 20. A first wireless device (WD) 22a located in coverage area 18a is configured to wirelessly connect to, or be paged by, the corresponding network node 16a. A second WD 22b in coverage area 18b is wirelessly connectable to the corresponding network node 16b. While a plurality of WDs 22a, 22b (collectively referred to as wireless devices 22) are illustrated in this example, the disclosed embodiments are equally applicable to a situation where a sole WD is in the coverage area or where a sole WD is connecting to the corresponding network node 16. Note that although only two WDs 22 and three network nodes 16 are shown for convenience, the communication system may include many more WDs 22 and network nodes 16. Also, it is contemplated that a WD 22 can be in simultaneous communication and/or configured to separately communicate with more than one network node 16 and more than one type of network node 16. For example, a WD 22 can have dual connectivity with a network node 16 that supports LTE and the same or a different network node 16 that supports NR. As an example, WD 22 can be in communication with an eNB for LTE/E-UTRAN and a gNB for NR/NG-RAN. The communication system 10 may itself be connected to a host computer 24, which may be embodied in the hardware and/or software of a standalone server, a cloud- implemented server, a distributed server or as processing resources in a server farm. The host computer 24 may be under the ownership or control of a service provider, or may be operated by the service provider or on behalf of the service provider. The connections 26, 28 between the communication system 10 and the host computer 24 may extend directly from the core network 14 to the host computer 24 or may extend via an optional intermediate network 30. The intermediate network 30 may be one of, or a combination of more than one of, a public, private or hosted network. The intermediate network 30, if any, may be a backbone network or the Internet. In some embodiments, the intermediate network 30 may comprise two or more sub-networks (not shown). The communication system of FIG.4 as a whole enables connectivity between one of the connected WDs 22a, 22b and the host computer 24. The connectivity may be described as an over-the-top (OTT) connection. The host computer 24 and the connected WDs 22a, 22b are configured to communicate data and/or signaling via the OTT connection, using the access network 12, the core network 14, any intermediate network 30 and possible further infrastructure (not shown) as intermediaries. The OTT connection may be transparent in the sense that at least some of the participating communication devices through which the OTT connection passes are unaware of routing of uplink and downlink communications. For example, a network node 16 may not or need not be informed about the past routing of an incoming downlink communication with data originating from a host computer 24 to be forwarded (e.g., handed over) to a connected WD 22a. Similarly, the network node 16 need not be aware of the future routing of an outgoing uplink communication originating from the WD 22a towards the host computer 24. A network node 16 is configured to include a selection unit 32 which is configured to perform one or more functions described herein such as, for example, with respect to reciprocity-based precoding schemes. A wireless device 22 is configured to include a TDCP unit 34 which is configured to perform one or more functions as described herein such as with respect to, for example, reciprocity-based precoding schemes. Example implementations, in accordance with an embodiment, of the WD 22, network node 16 and host computer 24 discussed in the preceding paragraphs will now be described with reference to FIG.5. In a communication system 10, a host computer 24 comprises hardware (HW) 38 including a communication interface 40 configured to set up and maintain a wired or wireless connection with an interface of a different communication device of the communication system 10. The host computer 24 further comprises processing circuitry 42, which may have storage and/or processing capabilities. The processing circuitry 42 may include a processor 44 and memory 46. In particular, in addition to or instead of a processor, such as a central processing unit, and memory, the processing circuitry 42 may comprise integrated circuitry for processing and/or control, e.g., one or more processors and/or processor cores and/or FPGAs (Field Programmable Gate Array) and/or ASICs (Application Specific Integrated Circuitry) adapted to execute instructions. The processor 44 may be configured to access (e.g., write to and/or read from) memory 46, which may comprise any kind of volatile and/or nonvolatile memory, e.g., cache and/or buffer memory and/or RAM (Random Access Memory) and/or ROM (Read-Only Memory) and/or optical memory and/or EPROM (Erasable Programmable Read-Only Memory). Processing circuitry 42 may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by host computer 24. Processor 44 corresponds to one or more processors 44 for performing host computer 24 functions described herein. The host computer 24 includes memory 46 that is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software 48 and/or the host application 50 may include instructions that, when executed by the processor 44 and/or processing circuitry 42, causes the processor 44 and/or processing circuitry 42 to perform the processes described herein with respect to host computer 24. The instructions may be software associated with the host computer 24. The software 48 may be executable by the processing circuitry 42. The software 48 includes a host application 50. The host application 50 may be operable to provide a service to a remote user, such as a WD 22 connecting via an OTT connection 52 terminating at the WD 22 and the host computer 24. In providing the service to the remote user, the host application 50 may provide user data which is transmitted using the OTT connection 52. The “user data” may be data and information described herein as implementing the described functionality. In one embodiment, the host computer 24 may be configured for providing control and functionality to a service provider and may be operated by the service provider or on behalf of the service provider. The processing circuitry 42 of the host computer 24 may enable the host computer 24 to observe, monitor, control, transmit to and/or receive from the network node 16 and or the wireless device 22. The processing circuitry 42 of the host computer 24 may include an information unit 54 configured to enable the service provider to one or more of transmit, receive, communication, forward, relay, determine, analyze, store, process, etc. information related to reciprocity-based precoding schemes. The communication system 10 further includes a network node 16 provided in a communication system 10 and including hardware 58 enabling it to communicate with the host computer 24 and with the WD 22. The hardware 58 may include a communication interface 60 for setting up and maintaining a wired or wireless connection with an interface of a different communication device of the communication system 10, as well as a radio interface 62 for setting up and maintaining at least a wireless connection 64 with a WD 22 located in a coverage area 18 served by the network node 16. The radio interface 62 may be formed as or may include, for example, one or more RF transmitters, one or more RF receivers, and/or one or more RF transceivers. The communication interface 60 may be configured to facilitate a connection 66 to the host computer 24. The connection 66 may be direct or it may pass through a core network 14 of the communication system 10 and/or through one or more intermediate networks 30 outside the communication system 10. In the embodiment shown, the hardware 58 of the network node 16 further includes processing circuitry 68. The processing circuitry 68 may include a processor 70 and a memory 72. In particular, in addition to or instead of a processor, such as a central processing unit, and memory, the processing circuitry 68 may comprise integrated circuitry for processing and/or control, e.g., one or more processors and/or processor cores and/or FPGAs (Field Programmable Gate Array) and/or ASICs (Application Specific Integrated Circuitry) adapted to execute instructions. The processor 70 may be configured to access (e.g., write to and/or read from) the memory 72, which may comprise any kind of volatile and/or nonvolatile memory, e.g., cache and/or buffer memory and/or RAM (Random Access Memory) and/or ROM (Read-Only Memory) and/or optical memory and/or EPROM (Erasable Programmable Read-Only Memory). Thus, the network node 16 further has software 74 stored internally in, for example, memory 72, or stored in external memory (e.g., database, storage array, network storage device, etc.) accessible by the network node 16 via an external connection. The software 74 may be executable by the processing circuitry 68. The processing circuitry 68 may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by network node 16. Processor 70 corresponds to one or more processors 70 for performing network node 16 functions described herein. The memory 72 is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software 74 may include instructions that, when executed by the processor 70 and/or processing circuitry 68, causes the processor 70 and/or processing circuitry 68 to perform the processes described herein with respect to network node 16. For example, processing circuitry 68 of the network node 16 may include selection unit 32 configured to perform one or more functions as described herein such as with respect to, for example, reciprocity-based precoding schemes. The communication system 10 further includes the WD 22 already referred to. The WD 22 may have hardware 80 that may include a radio interface 82 configured to set up and maintain a wireless connection 64 with a network node 16 serving a coverage area 18 in which the WD 22 is currently located. The radio interface 82 may be formed as or may include, for example, one or more RF transmitters, one or more RF receivers, and/or one or more RF transceivers. The hardware 80 of the WD 22 further includes processing circuitry 84. The processing circuitry 84 may include a processor 86 and memory 88. In particular, in addition to or instead of a processor, such as a central processing unit, and memory, the processing circuitry 84 may comprise integrated circuitry for processing and/or control, e.g., one or more processors and/or processor cores and/or FPGAs (Field Programmable Gate Array) and/or ASICs (Application Specific Integrated Circuitry) adapted to execute instructions. The processor 86 may be configured to access (e.g., write to and/or read from) memory 88, which may comprise any kind of volatile and/or nonvolatile memory, e.g., cache and/or buffer memory and/or RAM (Random Access Memory) and/or ROM (Read-Only Memory) and/or optical memory and/or EPROM (Erasable Programmable Read-Only Memory). Thus, the WD 22 may further comprise software 90, which is stored in, for example, memory 88 at the WD 22, or stored in external memory (e.g., database, storage array, network storage device, etc.) accessible by the WD 22. The software 90 may be executable by the processing circuitry 84. The software 90 may include a client application 92. The client application 92 may be operable to provide a service to a human or non-human user via the WD 22, with the support of the host computer 24. In the host computer 24, an executing host application 50 may communicate with the executing client application 92 via the OTT connection 52 terminating at the WD 22 and the host computer 24. In providing the service to the user, the client application 92 may receive request data from the host application 50 and provide user data in response to the request data. The OTT connection 52 may transfer both the request data and the user data. The client application 92 may interact with the user to generate the user data that it provides. The processing circuitry 84 may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by WD 22. The processor 86 corresponds to one or more processors 86 for performing WD 22 functions described herein. The WD 22 includes memory 88 that is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software 90 and/or the client application 92 may include instructions that, when executed by the processor 86 and/or processing circuitry 84, causes the processor 86 and/or processing circuitry 84 to perform the processes described herein with respect to WD 22. For example, the processing circuitry 84 of the wireless device 22 may include a TDCP unit 34 configured to perform one or more functions as described herien such as with respect to, for example, reciprocity-based precoding schemes. In some embodiments, the inner workings of the network node 16, WD 22, and host computer 24 may be as shown in FIG.5 and independently, the surrounding network topology may be that of FIG.4. In FIG.5, the OTT connection 52 has been drawn abstractly to illustrate the communication between the host computer 24 and the wireless device 22 via the network node 16, without explicit reference to any intermediary devices and the precise routing of messages via these devices. Network infrastructure may determine the routing, which it may be configured to hide from the WD 22 or from the service provider operating the host computer 24, or both. While the OTT connection 52 is active, the network infrastructure may further take decisions by which it dynamically changes the routing (e.g., on the basis of load balancing consideration or reconfiguration of the network). The wireless connection 64 between the WD 22 and the network node 16 is in accordance with the teachings of the embodiments described throughout this disclosure. One or more of the various embodiments improve the performance of OTT services provided to the WD 22 using the OTT connection 52, in which the wireless connection 64 may form the last segment. More precisely, the teachings of some of these embodiments may improve the data rate, latency, and/or power consumption and thereby provide benefits such as reduced user waiting time, relaxed restriction on file size, better responsiveness, extended battery lifetime, etc. In some embodiments, a measurement procedure may be provided for the purpose of monitoring data rate, latency and other factors on which the one or more embodiments improve. There may further be an optional network functionality for reconfiguring the OTT connection 52 between the host computer 24 and WD 22, in response to variations in the measurement results. The measurement procedure and/or the network functionality for reconfiguring the OTT connection 52 may be implemented in the software 48 of the host computer 24 or in the software 90 of the WD 22, or both. In embodiments, sensors (not shown) may be deployed in or in association with communication devices through which the OTT connection 52 passes; the sensors may participate in the measurement procedure by supplying values of the monitored quantities exemplified above, or supplying values of other physical quantities from which software 48, 90 may compute or estimate the monitored quantities. The reconfiguring of the OTT connection 52 may include message format, retransmission settings, preferred routing etc.; the reconfiguring need not affect the network node 16, and it may be unknown or imperceptible to the network node 16. Some such procedures and functionalities may be known and practiced in the art. In certain embodiments, measurements may involve proprietary WD signaling facilitating the host computer’s 24 measurements of throughput, propagation times, latency and the like. In some embodiments, the measurements may be implemented in that the software 48, 90 causes messages to be transmitted, in particular empty or ‘dummy’ messages, using the OTT connection 52 while it monitors propagation times, errors, etc. Thus, in some embodiments, the host computer 24 includes processing circuitry 42 configured to provide user data and a communication interface 40 that is configured to forward the user data to a cellular network for transmission to the WD 22. In some embodiments, the cellular network also includes the network node 16 with a radio interface 62. In some embodiments, the network node 16 is configured to, and/or the network node’s 16 processing circuitry 68 is configured to perform the functions and/or methods described herein for preparing/initiating/maintaining/supporting/ending a transmission to the WD 22, and/or preparing/terminating/maintaining/supporting/ending in receipt of a transmission from the WD 22. In some embodiments, the host computer 24 includes processing circuitry 42 and a communication interface 40 that is configured to a communication interface 40 configured to receive user data originating from a transmission from a WD 22 to a network node 16. In some embodiments, the WD 22 is configured to, and/or comprises a radio interface 82 and/or processing circuitry 84 configured to perform the functions and/or methods described herein for preparing/initiating/maintaining/supporting/ending a transmission to the network node 16, and/or preparing/terminating/maintaining/supporting/ending in receipt of a transmission from the network node 16. Although FIGS.4 and 5 show various “units” such as selection unit 32, and TDCP unit 34 as being within a respective processor, it is contemplated that these units may be implemented such that a portion of the unit is stored in a corresponding memory within the processing circuitry. In other words, the units may be implemented in hardware or in a combination of hardware and software within the processing circuitry. FIG.6 is a flowchart illustrating an exemplary method implemented in a communication system, such as, for example, the communication system of FIGS.4 and 5, in accordance with one embodiment. The communication system may include a host computer 24, a network node 16 and a WD 22, which may be those described with reference to FIG.5. In a first step of the method, the host computer 24 provides user data (Block S100). In an optional substep of the first step, the host computer 24 provides the user data by executing a host application, such as, for example, the host application 50 (Block S102). In a second step, the host computer 24 initiates a transmission carrying the user data to the WD 22 (Block S104). In an optional third step, the network node 16 transmits to the WD 22 the user data which was carried in the transmission that the host computer 24 initiated, in accordance with the teachings of the embodiments described throughout this disclosure (Block S106). In an optional fourth step, the WD 22 executes a client application, such as, for example, the client application 92, associated with the host application 50 executed by the host computer 24 (Block S108). FIG.7 is a flowchart illustrating an exemplary method implemented in a communication system, such as, for example, the communication system of FIG.4, in accordance with one embodiment. The communication system may include a host computer 24, a network node 16 and a WD 22, which may be those described with reference to FIGS.4 and 5. In a first step of the method, the host computer 24 provides user data (Block S110). In an optional substep (not shown) the host computer 24 provides the user data by executing a host application, such as, for example, the host application 50. In a second step, the host computer 24 initiates a transmission carrying the user data to the WD 22 (Block S112). The transmission may pass via the network node 16, in accordance with the teachings of the embodiments described throughout this disclosure. In an optional third step, the WD 22 receives the user data carried in the transmission (Block S114). FIG.8 is a flowchart illustrating an exemplary method implemented in a communication system, such as, for example, the communication system of FIG.4, in accordance with one embodiment. The communication system may include a host computer 24, a network node 16 and a WD 22, which may be those described with reference to FIGS.4 and 5. In an optional first step of the method, the WD 22 receives input data provided by the host computer 24 (Block S116). In an optional substep of the first step, the WD 22 executes the client application 92, which provides the user data in reaction to the received input data provided by the host computer 24 (Block S118). Additionally or alternatively, in an optional second step, the WD 22 provides user data (Block S120). In an optional substep of the second step, the WD provides the user data by executing a client application, such as, for example, client application 92 (Block S122). In providing the user data, the executed client application 92 may further consider user input received from the user. Regardless of the specific manner in which the user data was provided, the WD 22 may initiate, in an optional third substep, transmission of the user data to the host computer 24 (Block S124). In a fourth step of the method, the host computer 24 receives the user data transmitted from the WD 22, in accordance with the teachings of the embodiments described throughout this disclosure (Block S126). FIG.9 is a flowchart illustrating an exemplary method implemented in a communication system, such as, for example, the communication system of FIG.4, in accordance with one embodiment. The communication system may include a host computer 24, a network node 16 and a WD 22, which may be those described with reference to FIGS.4 and 5. In an optional first step of the method, in accordance with the teachings of the embodiments described throughout this disclosure, the network node 16 receives user data from the WD 22 (Block S128). In an optional second step, the network node 16 initiates transmission of the received user data to the host computer 24 (Block S130). In a third step, the host computer 24 receives the user data carried in the transmission initiated by the network node 16 (Block S132). FIG.10 is a flowchart of an exemplary process in a network node 16 according to one or more embodiments of the present disclosure. One or more blocks described herein may be performed by one or more elements of network node 16 such as by one or more of processing circuitry 68 (including the selection unit 32), processor 70, radio interface 62 and/or communication interface 60. Network node 16 is configured to select (Block S134) a reciprocity precoding scheme based on information related to a degree of time-variation of a channel, the information being associated with the wireless device 22, as described herein. According to one or more embodiments, the information related to the degree of time-variation of the channel is included in time-domain channel property, TDCP, feedback from the wireless device 22. According to one or more embodiments, the information related to the degree of time-variation of the channel comprises an amplitude of a normalized autocorrelation. According to one or more embodiments, if the amplitude of the normalized autocorrelation is less than a predefined threshold, the selection of the reciprocity precoding scheme is based on the reciprocity precoding scheme being robust to channel variations. According to one or more embodiments, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a sounding reference signal, SRS, periodicity is greater than a second predefined threshold, the selection of the reciprocity precoding scheme is based on the reciprocity precoding scheme being robust to channel variations. According to one or more embodiments, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a signal to noise ratio, SNR, of a received sounding reference signal, SRS, is less than a second predefined threshold, the selection of the reciprocity precoding scheme is based on the reciprocity precoding scheme being robust to channel variations. According to one or more embodiments, the reciprocity precoding scheme that is selected is a grid of beams, GoB, based scheme where a spatial stream towards the wireless device 22 is restricted to a single beam selected from a codebook of spatial beams. According to one or more embodiments, the processing circuitry 68 is further configured to at least one of: schedule the wireless device 22 for a single-user multiple- input multiple-output, SU-MIMO, transmission based on the amplitude of the normalized autocorrelation being below a threshold; and schedule the wireless device 22 for a multi- user MIMO, MU-MIMO, transmission based on the amplitude of the normalized autocorrelation being above a threshold; According to one or more embodiments, the processing circuitry 68 is further configured to perform channel prediction corresponding to a future slot based on uplink channels measured across different sounding reference signals, SRSs, instances transmitted by the wireless device 22 based on the amplitude of the normalized autocorrelation being below a threshold. According to one or more embodiments, the processing circuitry 68 is further configured to use a regularized precoder based on reciprocity, a regularization factor associated with the regularized precoder being based on the amplitude of the normalized autocorrelation. According to one or more embodiments, the regularization factor is inversely proportional to the amplitude of the normalized autocorrelation. According to one or more embodiments, the processing circuitry 68 is further configured to perform downlink transmission based on the selected reciprocity precoding scheme. FIG.11 is a flowchart of an exemplary process in a wireless device 22 according to some embodiments of the present disclosure. One or more blocks described herein may be performed by one or more elements of wireless device 22 such as by one or more of processing circuitry 84 (including the TDCP unit 34), processor 86, radio interface 82 and/or communication interface 60. Wireless device 22 is configured to determine (Block S136) information related to a degree of time-variation of a channel associated with the wireless device 22, as described herein. Wireless device 22is configured to transmit (Block S138) the information to the network node 16, as described herein. Wireless device is configured to receive (Block S140) a downlink transmission according to a reciprocity precoding scheme that is selected based on the information, as described herein. According to one or more embodiments, the information related to the degree of time-variation of the channel is included in time-domain channel property, TDCP, feedback from the wireless device 22. According to one or more embodiments, the information related to the degree of time-variation of the channel comprises an amplitude of a normalized autocorrelation. According to one or more embodiments, if the amplitude of the normalized autocorrelation is less than a predefined threshold, the reciprocity precoding scheme that is used for the downlink transmission being robust to channel variations. In one or more embodiments, the precoders selected by network node 16 are transparent to wireless device 22. According to one or more embodiments, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a sounding reference signal, SRS, periodicity is greater than a second predefined threshold, the reciprocity precoding scheme that is used for the downlink transmission being robust to channel variations. According to one or more embodiments, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a signal to noise ratio, SNR, of a received sounding reference signal, SRS, is less than a second predefined threshold, the reciprocity precoding scheme that is used for the downlink transmission being robust to channel variations. According to one or more embodiments, the reciprocity precoding scheme is based on a grid of beams, GoB, based scheme where a spatial stream towards the wireless device 22 is restricted to a single beam selected from a codebook of spatial beams. According to one or more embodiments, the processing circuitry 84 is further configured to receive an indication of at least one of: a scheduling of the wireless device 22 for a single-user multiple-input multiple-output, SU-MIMO, transmission based on the amplitude of the normalized autocorrelation being below a threshold; and a scheduling of the wireless device 22 for a multi-user MIMO, MU-MIMO, transmission based on the amplitude of the normalized autocorrelation being above a threshold. Having described the general process flow of arrangements of the disclosure and having provided examples of hardware and software arrangements for implementing the processes and functions of the disclosure, the sections below provide details and examples of arrangements for selection of one or more reciprocity-based precoding schemes. Some embodiments provide selection of one or more reciprocity-based precoding schemes. In one or more embodiments, the amplitude of the normalized autocorrelation reported in the TDCP feedback is used by network node 16 (e.g., gNB, TRP, scheduler, etc.) to switch between different types of reciprocity precoding schemes. In one or more embodiments, when the amplitude of the normalized autocorrelation corresponding to a configured autocorrelation delay for a wireless device 22 reported in the TDCP feedback is below a threshold, a reciprocity precoding scheme that is robust to channel variations is selected for the wireless device by network node 16 (e.g., gNB, TRP, scheduler, etc.). In one or more embodiments, when the amplitude of the normalized autocorrelation corresponding to a configured autocorrelation delay for a wireless device 22 reported in the TDCP feedback is below a threshold and the SRS periodicity is above a threshold, a reciprocity precoding scheme that is robust to channel variations is selected by network node 16 (e.g., gNB, TRP, scheduler, etc.). In one or more embodiments, when the amplitude of the normalized autocorrelation corresponding to a configured autocorrelation delay for wireless device 22 reported in the TDCP feedback is below a threshold or the SNR of the received SRS is below a threshold, a reciprocity precoding scheme that is robust to channel variations is selected by network node 16 (e.g., gNB, TRP, scheduler, etc.). An example of a reciprocity precoding scheme that is robust to channel variations is a simplified grid of beams (GoB) based scheme, where a spatial stream towards wireless device 22 is restricted to a single beam selected from a codebook of spatial beams. Typically, although not restrictive, such a codebook of beamforming vectors is composed of DFT vectors. In one or more embodiments, the number of spatial streams or the rank selected for wireless device is restricted to a rank r by network node 16 (e.g., gNB, TRP, scheduler, etc.) when the amplitude of the normalized autocorrelation corresponding to a configured autocorrelation delay reported in the TDCP feedback is below a certain threshold. In one or more embodiments, wireless device 22 is scheduled for a single-user MIMO transmission by network node 16 (e.g., gNB, TRP, scheduler, etc.) when the amplitude of the normalized autocorrelation corresponding to a configured autocorrelation delay reported in the TDCP feedback is below a certain threshold. In one or more embodiments, when the amplitude of the normalized autocorrelation corresponding to a configured autocorrelation delay reported in the TDCP feedback is above a threshold, the wireless device 22 is scheduled by network node 16 (e.g., gNB, TRP, scheduler, etc.) for a multi-user MIMO transmission. In one or more embodiments, when the amplitude of the normalized autocorrelation corresponding to a configured autocorrelation delay reported in the TDCP feedback is below a threshold, network node 16 (e.g., gNB, TRP, scheduler, etc.) may perform combining of the uplink channels measured across different SRS instances transmitted by the wireless device 22 to improve channel estimation. An example of combining is to average the channel measured at different time instances. The combined channel is then used to compute the precoder for at least one of the following: ^ to schedule wireless device 22 for a multi-user MIMO transmission; and ^ to compute a MU-MIMO precoder using channel reciprocity. In one or more embodiments, when the amplitude of the normalized autocorrelation, corresponding to a configured autocorrelation delay, reported in the TDCP feedback is below a threshold, a precoder is calculated using the transmitter side channel correlation matrix that captures the second order statistics of the channel which vary slowly over time is used by network node 16 (e.g., gNB, TRP, scheduler, etc.). In one or more embodiments, when the amplitude of the normalized autocorrelation corresponding to a configured autocorrelation delay reported in the TDCP feedback is below a threshold, network node 16 (e.g., gNB, TRP, scheduler, etc.) may enable channel prediction corresponding to a future slot based on uplink channels measured across different SRS instances transmitted by the wireless device 22. The predicted channel is then used to compute the precoder for at least one of the following: • to schedule wireless device 22 for a single-user MIMO transmission, • to compute a reciprocity precoder scheme that is robust to channel variations according to the above embodiments. In one or more embodiments, a regularized precoder based on reciprocity is used by network node 16 (e.g., gNB, TRP, scheduler, etc.), where the regularization factor is determined based on the amplitude of the normalized autocorrelation, corresponding to a configured autocorrelation delay, reported in the TDCP feedback. Examples of a regularized precoder are regularized zero-forcing, signal-to-leakage-and-noise ratio (SLNR), and minimum mean square error (MMSE) precoders. In one or more embodiments, the regularization factor is inversely proportional to the amplitude of the normalized autocorrelation. Non-limiting example Example 1. A method implemented by a network node 16, transmission reception point (TRP) or scheduler for determining a channel reciprocity-based precoding scheme based on normalized autocorrelation reports received from a wireless device 22, wherein the method comprises one or more of: • receiving a normalized autocorrelation value for a configured autocorrelation delay as part of a TDCP report from the wireless device 22; • measuring the UL channel based on SRS transmitted by the wireless device 22 in one or more time instances; • performing a first action when the normalized autocorrelation value is above a threshold, and performing a second action when the normalized autocorrelation value is below a threshold wherein the first action comprises at least one of: o scheduling the wireless device 22 for a multi-user MIMO transmission o performing combining of UL channel measured across different instances of the SRS transmitted by the wireless device 22, and using the combined channel for computing a precoder; and performing the second action comprises at least one of o computing a channel reciprocity-based precoder that is robust to channel variations o scheduling the wireless device 22 for a single-user MIMO transmission o restricting the rank or number of spatial layers for the wireless device 22 o performing channel prediction corresponding to a future slot based on measured UL channel across different SRS instances transmitted by the wireless device 22, and using the predicted channel for computing a precoder. • using the normalized autocorrelation value for a configured autocorrelation delay for determining the regularization factor in a regularized precoder. Hence, one or more embodiments and/or examples described herein provide one or more of the following advantages. The solutions described herein make reciprocity-based precoding adaptive to how fast the MIMO channel varies in time. This advantageously makes the precoding more robust to time variations of the MIMO channel while utilizing richer (e.g., more and/or better) channel information for slowly varying channels. This will maximize throughput for both moving and stationary wireless devices and increase the network capacity. Some embodiments may include one or more of the following: Embodiment A1. A network node configured to communicate with a wireless device, the network node configured to, and/or comprising a radio interface and/or comprising processing circuitry configured to: select a reciprocity precoding scheme based on information related to a degree of time-variation of a channel, the information being associated with the wireless device. Embodiment A2. The network node of Embodiment A1, wherein the information related to the degree of time-variation of the channel is included in time- domain channel property, TDCP, feedback from the wireless device. Embodiment A3. The network node of any one of Embodiments A1-A2, wherein the information related to the degree of time-variation of the channel comprises an amplitude of a normalized autocorrelation. Embodiment A4. The network node of Embodiment A3, wherein, if the amplitude of the normalized autocorrelation is less than a predefined threshold, the selection of the reciprocity precoding scheme is based on the reciprocity precoding scheme being robust to channel variations. Embodiment A5. The network node of Embodiment A3, wherein, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a sounding reference signal, SRS, periodicity is greater than a second predefined threshold, the selection of the reciprocity precoding scheme is based on the reciprocity precoding scheme being robust to channel variations. Embodiment A6. The network node of Embodiment A3, wherein, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a signal to noise ratio, SNR, of a received sounding reference signal, SRS, is less than a second predefined threshold, the selection of the reciprocity precoding scheme is based on the reciprocity precoding scheme being robust to channel variations. Embodiment A7. The network node of any one of Embodiments A1-A6, wherein the reciprocity precoding scheme that is selected is a grid of beams, GoB, based scheme where a spatial stream towards the wireless device is restricted to a single beam selected from a codebook of spatial beams. Embodiment A8. The network node of Embodiment A3, wherein the processing circuitry is further configured to at least one of: schedule the wireless device for a single-user multiple-input multiple-output, SU- MIMO, transmission based on the amplitude of the normalized autocorrelation being below a threshold; schedule the wireless device for a multi-user MIMO, MU-MIMO, transmission based on the amplitude of the normalized autocorrelation being above a threshold; Embodiment A9. The network node of Embodiment A3, wherein the processing circuitry is further configured to perform channel prediction corresponding to a future slot based on uplink channels measured across different sounding reference signals, SRSs, instances transmitted by the wireless device based on the amplitude of the normalized autocorrelation being below a threshold. Embodiment A10. The network node of Embodiment A3, wherein the processing circuitry is further configured to use a regularized precoder based on reciprocity, a regularization factor associated with the regularized precoder being based on the amplitude of the normalized autocorrelation. Embodiment A11. The network node of Embodiment A10, wherein the regularization factor is inversely proportional to the amplitude of the normalized autocorrelation. Embodiment A12. The network node of any one of Embodiments A1-A11, wherein the processing circuitry is further configured to perform downlink transmission based on the selected reciprocity precoding scheme. Embodiment B1. A method implemented by a network node that is configured to communicate with a wireless device, the method comprising: selecting a reciprocity precoding scheme based on information related to a degree of time-variation of a channel, the information being associated with the wireless device. Embodiment B2. The method of Embodiment B1, wherein the information related to the degree of time-variation of the channel is included in time-domain channel property, TDCP, feedback from the wireless device. Embodiment B3. The method of any one of Embodiments B1-B2, wherein the information related to the degree of time-variation of the channel comprises an amplitude of a normalized autocorrelation. Embodiment B4. The method of Embodiment B3, wherein, if the amplitude of the normalized autocorrelation is less than a predefined threshold, the selection of the reciprocity precoding scheme is based on the reciprocity precoding scheme being robust to channel variations. Embodiment B5. The method of Embodiment B3, wherein, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a sounding reference signal, SRS, periodicity is greater than a second predefined threshold, the selection of the reciprocity precoding scheme is based on the reciprocity precoding scheme being robust to channel variations. Embodiment B6. The method of Embodiment B3, wherein, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a signal to noise ratio, SNR, of a received sounding reference signal, SRS, is less than a second predefined threshold, the selection of the reciprocity precoding scheme is based on the reciprocity precoding scheme being robust to channel variations. Embodiment B7. The method of any one of Embodiments B1-B6, wherein the reciprocity precoding scheme that is selected is a grid of beams, GoB, based scheme where a spatial stream towards the wireless device is restricted to a single beam selected from a codebook of spatial beams. Embodiment B8. The method of Embodiment B3, further comprising at least one of: scheduling the wireless device for a single-user multiple-input multiple-output, SU-MIMO, transmission based on the amplitude of the normalized autocorrelation being below a threshold; and scheduling the wireless device for a multi-user MIMO, MU-MIMO, transmission based on the amplitude of the normalized autocorrelation being above a threshold; Embodiment B9. The method of Embodiment B3, further comprising performing channel prediction corresponding to a future slot based on uplink channels measured across different sounding reference signals, SRSs, instances transmitted by the wireless device based on the amplitude of the normalized autocorrelation being below a threshold. Embodiment B10. The method of Embodiment B3, further comprising using a regularized precoder based on reciprocity, a regularization factor associated with the regularized precoder being based on the amplitude of the normalized autocorrelation. Embodiment B11. The method of Embodiment B10, wherein the regularization factor is inversely proportional to the amplitude of the normalized autocorrelation. Embodiment B12. The method of any one of Embodiments B1-B11, further comprising performing downlink transmission based on the selected reciprocity precoding scheme. Embodiment C1. A wireless device configured to communicate with a network node, the wireless device configured to, and/or comprising a radio interface and/or processing circuitry configured to: determine information related to a degree of time-variation of a channel associated with the wireless device; transmit the information to the network node; and receive a downlink transmission according to a reciprocity precoding scheme that is selected based on the information. Embodiment C2. The wireless device of Embodiment C1, wherein the information related to the degree of time-variation of the channel is included in time- domain channel property, TDCP, feedback from the wireless device. Embodiment C3. The wireless device of any one of Embodiments C1-C2, wherein the information related to the degree of time-variation of the channel comprises an amplitude of a normalized autocorrelation. Embodiment C4. The wireless device of Embodiment C3, wherein, if the amplitude of the normalized autocorrelation is less than a predefined threshold, the reciprocity precoding scheme that is used for the downlink transmission being robust to channel variations. Embodiment C5. The wireless device of Embodiment C3, wherein, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a sounding reference signal, SRS, periodicity is greater than a second predefined threshold, the reciprocity precoding scheme that is used for the downlink transmission being robust to channel variations. Embodiment C6. The wireless device of Embodiment C3, wherein, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a signal to noise ratio, SNR, of a received sounding reference signal, SRS, is less than a second predefined threshold, the reciprocity precoding scheme that is used for the downlink transmission being robust to channel variations. Embodiment C7. The wireless device of any one of Embodiments C1-C6, wherein the reciprocity precoding scheme is based on a grid of beams, GoB, based scheme where a spatial stream towards the wireless device is restricted to a single beam selected from a codebook of spatial beams. Embodiment D1. A method implemented by a wireless device that is configured to communicate with a network node, the method comprising: determining information related to a degree of time-variation of a channel associated with the wireless device; transmitting the information to the network node; and receiving a downlink transmission according to a reciprocity precoding scheme that is selected based on the information. Embodiment D2. The method of Embodiment D1, wherein the information related to the degree of time-variation of the channel is included in time-domain channel property, TDCP, feedback from the wireless device. Embodiment D3. The method of any one of Embodiments D1-D2, wherein the information related to the degree of time-variation of the channel comprises an amplitude of a normalized autocorrelation. Embodiment D4. The method of Embodiment D3, wherein, if the amplitude of the normalized autocorrelation is less than a predefined threshold, the reciprocity precoding scheme that is used for the downlink transmission being robust to channel variations. Embodiment D5. The method of Embodiment D3, wherein, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a sounding reference signal, SRS, periodicity is greater than a second predefined threshold, the reciprocity precoding scheme that is used for the downlink transmission being robust to channel variations. Embodiment D6. The method of Embodiment D3, wherein, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a signal to noise ratio, SNR, of a received sounding reference signal, SRS, is less than a second predefined threshold, the reciprocity precoding scheme that is used for the downlink transmission being robust to channel variations. Embodiment D7. The method of any one of Embodiments D1-D6, wherein the reciprocity precoding scheme is based on a grid of beams, GoB, based scheme where a spatial stream towards the wireless device is restricted to a single beam selected from a codebook of spatial beams. Embodiment D8. The method of Embodiment D3, further comprising receiving at least one of: a scheduling of the wireless device for a single-user multiple-input multiple-output, SU-MIMO, transmission based on the amplitude of the normalized autocorrelation being below a threshold; and a scheduling of the wireless device for a multi-user MIMO, MU-MIMO, transmission based on the amplitude of the normalized autocorrelation being above a threshold. As will be appreciated by one of skill in the art, the concepts described herein may be embodied as a method, data processing system, computer program product and/or computer storage media storing an executable computer program. Accordingly, the concepts described herein may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects all generally referred to herein as a “circuit” or “module.” Any process, step, action and/or functionality described herein may be performed by, and/or associated to, a corresponding module, which may be implemented in software and/or firmware and/or hardware. Furthermore, the disclosure may take the form of a computer program product on a tangible computer usable storage medium having computer program code embodied in the medium that can be executed by a computer. Any suitable tangible computer readable medium may be utilized including hard disks, CD-ROMs, electronic storage devices, optical storage devices, or magnetic storage devices. Some embodiments are described herein with reference to flowchart illustrations and/or block diagrams of methods, systems and computer program products. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer (to thereby create a special purpose computer), special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. These computer program instructions may also be stored in a computer readable memory or storage medium that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer readable memory produce an article of manufacture including instruction means which implement the function/act specified in the flowchart and/or block diagram block or blocks. The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. It is to be understood that the functions/acts noted in the blocks may occur out of the order noted in the operational illustrations. For example, two blocks shown in succession may in fact be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality/acts involved. Although some of the diagrams include arrows on communication paths to show a primary direction of communication, it is to be understood that communication may occur in the opposite direction to the depicted arrows. Computer program code for carrying out operations of the concepts described herein may be written in an object oriented programming language such as Python, Java® or C++. However, the computer program code for carrying out operations of the disclosure may also be written in conventional procedural programming languages, such as the "C" programming language. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer. In the latter scenario, the remote computer may be connected to the user's computer through a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). Many different embodiments have been disclosed herein, in connection with the above description and the drawings. It will be understood that it would be unduly repetitious and obfuscating to literally describe and illustrate every combination and subcombination of these embodiments. Accordingly, all embodiments can be combined in any way and/or combination, and the present specification, including the drawings, shall be construed to constitute a complete written description of all combinations and subcombinations of the embodiments described herein, and of the manner and process of making and using them, and shall support claims to any such combination or subcombination. It will be appreciated by persons skilled in the art that the embodiments described herein are not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope of the following claims. .

Claims

What is claimed is: 1. A network node configured to communicate with a wireless device, the network node configured to, and/or comprising a radio interface and/or comprising processing circuitry configured to: select a reciprocity precoding scheme based on information related to a degree of time-variation of a channel, the information being associated with the wireless device.
2. The network node of claim 1, wherein the information related to the degree of time-variation of the channel is included in time-domain channel property, TDCP, feedback from the wireless device.
3. The network node of any one of claims 1-2, wherein the information related to the degree of time-variation of the channel comprises an amplitude of a normalized autocorrelation.
4. The network node of claim 3, wherein, if the amplitude of the normalized autocorrelation is less than a predefined threshold, the selection of the reciprocity precoding scheme is based on the reciprocity precoding scheme being robust to channel variations.
5. The network node of claim 3, wherein, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a sounding reference signal, SRS, periodicity is greater than a second predefined threshold, the selection of the reciprocity precoding scheme is based on the reciprocity precoding scheme being robust to channel variations.
6. The network node of claim 3, wherein, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a signal to noise ratio, SNR, of a received sounding reference signal, SRS, is less than a second predefined threshold, the selection of the reciprocity precoding scheme is based on the reciprocity precoding scheme being robust to channel variations.
7. The network node of any one of claims 1- 6, wherein the reciprocity precoding scheme that is selected is a grid of beams, GoB, based scheme where a spatial stream towards the wireless device is restricted to a single beam selected from a codebook of spatial beams.
8. The network node of claim 3, wherein the processing circuitry is further configured to at least one of: schedule the wireless device for a single-user multiple-input multiple-output, SU- MIMO, transmission based on the amplitude of the normalized autocorrelation being below a threshold; schedule the wireless device for a multi-user MIMO, MU-MIMO, transmission based on the amplitude of the normalized autocorrelation being above a threshold.
9. The network node of claim 3, wherein the processing circuitry is further configured to perform channel prediction corresponding to a future slot based on uplink channels measured across different sounding reference signals, SRSs, instances transmitted by the wireless device based on the amplitude of the normalized autocorrelation being below a threshold.
10. The network node of claim 3, wherein the processing circuitry is further configured to use a regularized precoder based on reciprocity, a regularization factor associated with the regularized precoder being based on the amplitude of the normalized autocorrelation.
11. The network node of claim 10, wherein the regularization factor is inversely proportional to the amplitude of the normalized autocorrelation.
12. The network node of any one of claims 1-11, wherein the processing circuitry is further configured to perform downlink transmission based on the selected reciprocity precoding scheme.
13. A method implemented by a network node that is configured to communicate with a wireless device, the method comprising: selecting a reciprocity precoding scheme based on information related to a degree of time-variation of a channel, the information being associated with the wireless device.
14. The method of claim 13, wherein the information related to the degree of time-variation of the channel is included in time-domain channel property, TDCP, feedback from the wireless device.
15. The method of any one of claims 13-14, wherein the information related to the degree of time-variation of the channel comprises an amplitude of a normalized autocorrelation.
16. The method of claim 15, wherein, if the amplitude of the normalized autocorrelation is less than a predefined threshold, the selection of the reciprocity precoding scheme is based on the reciprocity precoding scheme being robust to channel variations.
17. The method of claim 15, wherein, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a sounding reference signal, SRS, periodicity is greater than a second predefined threshold, the selection of the reciprocity precoding scheme is based on the reciprocity precoding scheme being robust to channel variations.
18. The method of claim 15, wherein, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a signal to noise ratio, SNR, of a received sounding reference signal, SRS, is less than a second predefined threshold, the selection of the reciprocity precoding scheme is based on the reciprocity precoding scheme being robust to channel variations.
19. The method of any one of claims 12-18, wherein the reciprocity precoding scheme that is selected is a grid of beams, GoB, based scheme where a spatial stream towards the wireless device is restricted to a single beam selected from a codebook of spatial beams.
20. The method of claim 15, further comprising at least one of: scheduling the wireless device for a single-user multiple-input multiple-output, SU-MIMO, transmission based on the amplitude of the normalized autocorrelation being below a threshold; and scheduling the wireless device for a multi-user MIMO, MU-MIMO, transmission based on the amplitude of the normalized autocorrelation being above a threshold.
21. The method of claim 15, further comprising performing channel prediction corresponding to a future slot based on uplink channels measured across different sounding reference signals, SRSs, instances transmitted by the wireless device based on the amplitude of the normalized autocorrelation being below a threshold.
22. The method of claim 15, further comprising using a regularized precoder based on reciprocity, a regularization factor associated with the regularized precoder being based on the amplitude of the normalized autocorrelation.
23. The method of claim 22, wherein the regularization factor is inversely proportional to the amplitude of the normalized autocorrelation.
24. The method of any one of claims 12-23, further comprising performing downlink transmission based on the selected reciprocity precoding scheme.
25. A wireless device configured to communicate with a network node, the wireless device configured to, and/or comprising a radio interface and/or processing circuitry configured to: determine information related to a degree of time-variation of a channel associated with the wireless device; transmit the information to the network node; and receive a downlink transmission according to a reciprocity precoding scheme that is selected based on the information.
26. The wireless device of claim 25, wherein the information related to the degree of time-variation of the channel is included in time-domain channel property, TDCP, feedback from the wireless device.
27. The wireless device of any one of claims 25-26, wherein the information related to the degree of time-variation of the channel comprises an amplitude of a normalized autocorrelation.
28. The wireless device of claim 27, wherein, if the amplitude of the normalized autocorrelation is less than a predefined threshold, the reciprocity precoding scheme that is used for the downlink transmission being robust to channel variations.
29. The wireless device of claim 27, wherein, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a sounding reference signal, SRS, periodicity is greater than a second predefined threshold, the reciprocity precoding scheme that is used for the downlink transmission being robust to channel variations.
30. The wireless device of claim 27, wherein, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a signal to noise ratio, SNR, of a received sounding reference signal, SRS, is less than a second predefined threshold, the reciprocity precoding scheme that is used for the downlink transmission being robust to channel variations.
31. The wireless device of any one of claims 25-30, wherein the reciprocity precoding scheme is based on a grid of beams, GoB, based scheme where a spatial stream towards the wireless device is restricted to a single beam selected from a codebook of spatial beams.
32. A method implemented by a wireless device that is configured to communicate with a network node, the method comprising: determining information related to a degree of time-variation of a channel associated with the wireless device; transmitting the information to the network node; and receiving a downlink transmission according to a reciprocity precoding scheme that is selected based on the information.
33. The method of claim 32, wherein the information related to the degree of time-variation of the channel is included in time-domain channel property, TDCP, feedback from the wireless device.
34. The method of any one of claims 32-33, wherein the information related to the degree of time-variation of the channel comprises an amplitude of a normalized autocorrelation.
35. The method of claim 34, wherein, if the amplitude of the normalized autocorrelation is less than a predefined threshold, the reciprocity precoding scheme that is used for the downlink transmission being robust to channel variations.
36. The method of claim 34, wherein, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a sounding reference signal, SRS, periodicity is greater than a second predefined threshold, the reciprocity precoding scheme that is used for the downlink transmission being robust to channel variations.
37. The method of claim 34, wherein, if the amplitude of the normalized autocorrelation is less than a first predefined threshold and a signal to noise ratio, SNR, of a received sounding reference signal, SRS, is less than a second predefined threshold, the reciprocity precoding scheme that is used for the downlink transmission being robust to channel variations.
38. The method of any one of claims 32-37, wherein the reciprocity precoding scheme is based on a grid of beams, GoB, based scheme where a spatial stream towards the wireless device is restricted to a single beam selected from a codebook of spatial beams.
39. The method of claim 34, further comprising receiving at least one of: a scheduling of the wireless device for a single-user multiple-input multiple-output, SU-MIMO, transmission based on the amplitude of the normalized autocorrelation being below a threshold; and a scheduling of the wireless device for a multi-user MIMO, MU-MIMO, transmission based on the amplitude of the normalized autocorrelation being above a threshold.
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