WO2017099869A1

WO2017099869A1 - Sounding reference signal transmission in standalone systems

Info

Publication number: WO2017099869A1
Application number: PCT/US2016/054546
Authority: WO
Inventors: Jeongho Jeon; Abhijeet Bhorkar; Qiaoyang Ye; Hwan-Joon Kwon; Huaning Niu
Original assignee: Intel IP Corp
Current assignee: Intel IP Corp
Priority date: 2015-12-07
Filing date: 2016-09-29
Publication date: 2017-06-15
Anticipated expiration: 2018-06-07

Abstract

Embodiments of sounding reference signal transmission in standalone systems are generally described herein. An exemplary apparatus of User Equipment (UE) may include memory, and processing circuitry. The processing circuitry to decode a request for transmission of a sounding reference signal (SRS) in unlicensed spectrum. The transmission is facilitated via license-assisted access (LAA). The processing circuitry further to perform a modified listen-before-talk (LBT) procedure, and in response to a clear channel assessment (CCA) made as part of the modified LBT procedure, encode the SRS for transmission. The processing circuitry further to decode an uplink (UL) grant, received via a physical downlink control channel (PDCCH), that includes assigned UL resources, wherein the assigned UL resources are based on the SRS.

Description

SOUNDING REFERENCE SIGNAL TRANSMISSION IN STANDALONE

SYSTEMS

PRIORITY CLAIM

[0001] This patent application claims the benefit of priority to U.S.

Provisional Patent Application Serial No. 62/336,009, filed on May 13, 2016, and U.S. Provisional Patent Application Serial Number 62/264,219, filed December 7, 2015, both of which are hereby incorporated by reference herein their entirety.

TECHNICAL FIELD

[0002] Embodiments pertain to cellular networks. Some embodiments relate to carrier aggregation in Third Generation Partnership Project Long Term Evolution (3 GPP LTE) networks and LTE advanced (LTE-A) networks, as well as 4^th generation (4G) networks and 5^th generation (5G) networks.

BACKGROUND

[0003] An enhancement for LTE in 3GPP Release 13 is enable operation in the unlicensed spectrum via Licensed-Assisted Access (LAA), which expands the system bandwidth by utilizing the flexible carrier aggregation (CA) framework. Potential LTE operation in unlicensed spectrum may include LTE operation in the unlicensed spectrum via dual connectivity (DC) or the standalone LTE system in the unlicensed spectrum.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] FIG. 1 a wireless telecommunications network 100 in accordance with some embodiments of the disclosure.

[0005] FIG. 2 illustrates a block diagram of components of a User

Equipment (UE) device in accordance with to embodiments of the disclosure. [0006] FIG. 3 illustrates a flow diagram of a method for a single interval listen-before-talk (LBT) procedure for transmission of SRS in an unlicensed spectrum in accordance with some embodiments of the disclosure.

[0007] FIG. 4 illustrates a flow diagram of a method for a LBT with random backoff procedure for transmission of SRS in an unlicensed spectrum in accordance with some embodiments of the disclosure.

[0008] FIG. 5 illustrates an exemplary signal diagram to showing SRS transmissions with different RPFs in the frequency domain in accordance with some embodiments of the disclosure.

[0009] FIG. 6 illustrates an exemplary signal diagram to showing SRS transmissions puncturing a DL burst in the time domain in accordance with some embodiments of the disclosure.

[0010] FIG. 7 illustrates a flow diagram of a method to transmit a sounding reference signal (SRS) in unlicensed spectrum in accordance with some embodiments of the disclosure.

[0011] FIG. 8 illustrates a flow diagram of a method to request a sounding reference signal (SRS) in unlicensed spectrum in accordance with some embodiments of the disclosure.

[0012] FIG. 9 illustrates a block diagram of a machine in the example form of a computer system in accordance with some embodiments of the disclosure.

[0013]

DETAILED DESCRIPTION

[0014] The following description and the drawings sufficiently illustrate specific embodiments to enable those skilled in the art to practice them. Other embodiments may incorporate structural, logical, electrical, process, and other changes. Portions and features of some embodiments may be included in, or substituted for, those of other embodiments. Embodiments set forth in the claims encompass available equivalents of those claims.

[0015] Embodiments provide systems and methods for sounding reference signal (SRS) transmission in unlicensed spectrum via License-Assisted Access (LAA). The SRSs may be used for channel estimation to enable frequency- selective scheduling. SRSs may also be used to support various start-up functions (initial modulation and coding scheme (MCS) selection, power control, etc.) for user equipments (UEs) that have not been scheduled for transmission recently. In LTE systems, the SRS transmissions occur in the last SC-FDMA symbol in a configured subframe. The subframes in which SRSs are transmitted by any UE within may be indicated by cell-specific broadcast signaling. However, SRS transmission in unlicensed spectrum is complicated by a listen-before-talk (LBT) protocol, which is a procedure whereby radio transmitters first sense the medium and transmit only if the medium is sensed to be idle, also called clear channel assessment (CCA). The CCA utilizes at least energy detection (ED) to determine the presence of signals on a channel. With the adoption of LBT, the SRS transmissions may not be guaranteed as configured by the network, which may negatively affect the performance of UL scheduling and the initial start-up functions such as the initial MCS selection and power control for UEs not recently scheduled.

[0016] FIG. 1 illustrates a wireless telecommunications network 100 in accordance with some embodiments of the disclosure. In some embodiments, the wireless telecommunications network 100 may implement 3rd Generation partnership Project (3GPP) fifth generation (5G) wireless network or 3GPP long term evolution advanced (LTE-A) wireless network.

[0017] The wireless telecommunications network 100 includes an evolved

Node B (eNodeB) 120 that is operable over corresponding a coverage area or cell 122, and a user equipment (UE) 104 within the coverage area of the cell 122. The telecommunications network 100 may include many more eNodeBs and/or UEs. The coverage area 122 of the eNodeB 120 may be further divided into three sectors. In some examples, each sector of the eNodeB 120 may also be viewed as a cell.

[0018] The UE 104 may provide transmissions to and receive transmissions from the eNodeB 120 in a licensed spectrum, an unlicensed spectrum, or combinations thereof. Operation in both the licensed spectrum and the unlicensed spectrum may include dual connectivity (DC) (e.g., connected to both contemporaneously). In some examples, operation in the unlicensed spectrum may be via LAA, which may expand available bandwidth by utilizing a flexible carrier aggregation (CA) framework. To prevent collisions, transmission in the unlicensed spectrum may include performing a LBT procedure, and holding transmission until making a CCA (e.g., an indication that the channel is idle or clear of other communication).

[0019] In operation, the wireless telecommunications network 100 may include a capability for the eNodeB 120 and the UE 104 to communicate over licensed spectrum. The wireless telecommunications network 100 may also include a capability for the eNodeB 120 and the UE 104 to communicate over unlicensed spectrum. In some examples of contemporaneous transmission over licensed and unlicensed spectrum, the licensed spectrum transmission may be a primary cell (PCell) transmissions and the unlicensed spectrum transmissions may be secondary cell (SCell) transmissions. For communication over the PCell and the SCell, the wireless telecommunications network 100 may use a self-contained frame structure in which control signaling and data may be transmitted with a single subframe in a time-division multiplexing (TDM) manner. For example, there may be two types of frame structure: one for downlink data transmission and another for uplink data transmission. To help support frequency-selective scheduling of transmissions, initial MCS selection, power control, etc., the eNodeB 120 may initiate (e.g., trigger) transmission of SRS signals by the UE 104. Triggering of the SRS transmission may be UE 104-specific downlink control information (DCI), or group DCI, with each UE, including the UE 104, assigned an exclusive resource for the SRS, which may be a comb-type (e.g., divided by subcarrier) SRS resource structure among the group or a cyclic-shift type (e.g., divided by time) SRS transmission among the group. Because of implementation of LBT in the unlicensed spectrum, the SRS transmissions may not be guaranteed as configured by the wireless telecommunications network 100, which may negatively affect performance of uplink (UL) scheduling.

[0020] In one embodiment to support SRS transmission in the unlicensed spectrum, the UE 104 may perform a modified LBT procedure. In some examples, the eNodeB 120 may indicate to the UE 104 in an SRS triggering message a type of LBT to be used for the SRS transmission. In one example, in response to a request from the eNodeB 120, the UE 104 may transmit the SRS without performing the LBT procedure. For example, if the SRS transmission occurs less than preconfigured time threshold (e.g., 16 μβ) after a downlink (DL) transmission, the LBT may be skipped. Additionally, even if the SRS transmission occurs outside of the preconfigured time threshold, because the SRS may only possess a very small portion of airtime (e.g., 1.4% of an unlicensed band in a case of a wideband SRS for 32 UEs with a 10ms periodicity), skipping the LBT procedure may have a small likelihood of interfering with other communications in the unlicensed spectrum.

[0021] In another example of a modified LBT procedure, the UE 104 may employ a single interval LBT procedure, where if a CCA is made after a single time interval, the SRS signal is transmitted. The single time interval may be 25 μβ, in some examples. If no CCA is made, then the SRS transmission is aborted. In some examples, the one shot LBT may be used for aperiodic SRS transmissions (e.g., requested by the eNodeB 120) without a physical uplink shared channel (PUSCH) within existing mean channel open time (MCOT).

[0022] In yet another example of a modified LBT procedure, the UE 104 may employ a LBT with random backoff procedure. In the LBT with random backoff procedure, the UE 104 may determine a random LBT count and a contention window size (CWS). The UE 104 may monitor a channel for the contention window timeframe, and then perform a CCA. If a CCA is made, the LBT count is decremented, and the process is repeated. So long as the CCA is made after each iteration, the process continues until the LBT count is zero. Once the LBT count is equal to zero, the SRS transmission is made. If the CCA is not made after any one of the iterations before the LBT count is equal to zero, then the process starts over. The LBT count may be any number from 3 to 7, in some examples. In some examples, the CWS may be fixed, such as 9 μβ. In other examples, the CWS may be variable. One of skill in the art will appreciate that, instead of decrementing a counter, a counter may be incremented until it reaches a random backoff count as part of the LBT with random backoff procedure.

[0023] In another embodiment to support SRS transmission in the unlicensed spectrum, the UE 104 may multiplex SRS transmissions with other UEs by transmitting the SRS over a subset of subcarriers in the designated frequency band. In some examples in LTE, a default subcarrier repetition factor (RPF) for SRS transmission in an unlicensed band for the UE 104 may be set to 2 (e.g., every other sub-carrier). To allow more UEs to multiplex their SRSs (e.g., for narrowband SRSs), the RPF may be increased to an integer N. For example, in a current LTE implementation, 16 UEs may be multiplexed in a single SRS procedure. If the RPF is increased to 4, then 32 UEs may be supported in a single SRS procedure. FIG. 5 illustrates an exemplary signal diagram 500 to showing SRS transmissions with different RPFs in the frequency domain in accordance with some embodiments of the disclosure. The carrier frequency may include subcarriers SC1-SC11. In a first example 510 where the RPF is 2, the SRS is transmitted on every other subcarrier (SCI, 3, 5, 7, 9, 11, etc.). In the second example 520 where the RPF is 4, the SRS is transmitted on every fourth subcarrier (SCI, 5, 9, etc.). As is depicted, doubling the RPC may double available slots for multiplexing other UEs.

[0024] In another embodiment to support SRS transmission in the unlicensed spectrum, the UE 104 may transmit the SRS with or without a PUSCH. Typically in LTE, the UE 104 may only transmit the SRS in a last symbol period of a configured/designated subframe. Thus, if the UE 104 transmits SRS only, then it may have to wait until the last symbol of the designated subframe for SRS transmission. This may cause the misalignment of the start/end of LBT of UEs or the UE has to wait for some time, i.e., until the last symbol, after finishing the LBT in the beginning of the subframe. To mitigate the timing issues, the UE 104 may have an option configuration where the SRS symbol position is moved to a first symbol of the designated subframe, in addition to the existing configuration for SRS symbol position to be the last symbol. The signaling can be done via, for example, layer one or layer 2 (L1/L2) signaling such as an enhanced physical downlink control channel (E-PDCCH), a MAC control element (CE), a radio resource control (RRC) signaling, or other higher layer signaling.

[0025] In another embodiment to support SRS transmission in the unlicensed spectrum, the UE 104 may interrupt (e.g., puncture) a downlink (DL) transmission burst to transmit a preconfigured SRS transmission. Interrupting the DL burst by the UE 104 may be available in unlicensed spectrum due to uncertainty in channel access opportunities and UL/DL configuration in frame structure Type 3. To support flexible system operation in unlicensed spectrum, LTE Release 13 introduced for LAA a new frame structure, called Type 3, in which each subframe can be either DL or UL. The UE 104 may consider each subframe as empty if no transmission in detected in that subframe. The detection may be accomplished via a method such as carrier routing system (CRS) presence detection. The interruption of the DL burst by the UE 104 may increase SRS transmission opportunities. It is appreciated that transitioning a radio of the UE 104 from DL to UL takes some time. Therefore, in some examples the interruption of the DL burst may also include interruption of one or more symbols before and after a symbol assigned for SRS transmission to allow radio turnaround time. In other examples, the UE 104 may shorten a time duration of an SRS signal by reducing the fast Fourier Transform (FFT) size of the transmission. For example, if the UE 104 reduces the FFT size by half, the SRS symbol duration may also be halved. The duration for SRS transmission, or equivalently the FFT size for SRS, may be signaled via L1/L2 signaling, such as E-PDCCH, MAC CE, RRC signaling, or other higher layer signaling. FIG. 6 illustrates an exemplary signal diagram 600 to showing SRS transmissions puncturing a DL burst in the time domain in accordance with some embodiments of the disclosure. The UE 104 may begin provide a first portion of a DL burst 610(1) and a second portion of a DL burst 610(2). The DL burst 610 may be interrupted by a SRS transmission 620. The length of the SRS transmission may be based on the FFT size, as previously described.

[0026] The SRS requested by the eNodeB 120 and/or transmitted by the

UE 104 may be a wideband SRS or a narrowband SRS. In an example, based on the SRS provided by the UE 104, the eNodeB 120 may assign UL resources to the UE 104 and may provide, via a physical downlink control channel (PDCCH), an uplink (UL) grant that includes the assigned UL resources to the UE 104. The UE 104 may transmit information using the assigned UL resources.

[0027] Embodiments described herein may be implemented into a system using any suitably configured hardware and/or software. Figure 2 illustrates a block diagram of components of a User Equipment (UE) device 200 according to embodiments of the disclosure. The UE 200 may be implemented in the UE 104 of Figure 1. In some embodiments, the UE device 200 may include application circuitry 202, baseband circuitry 204, Radio Frequency (RF) circuitry 206, front-end module (FEM) circuitry 208 and one or more antennas 210, coupled together at least as shown. [0028] The application circuitry 202 may include one or more application processors. For example, the application circuitry 202 may include circuitry such as, but not limited to, one or more single-core or multi-core processors. The processor(s) may include any combination of general-purpose processors and dedicated processors (e.g., graphics processors, application processors, etc.). The processors may be coupled with and/or may include memory/storage and may be configured to execute instructions stored in the memory/storage to enable various applications and/or operating systems to run on the system.

[0029] The baseband circuitry 204 may include circuitry such as, but not limited to, one or more single-core or multi-core processors. The baseband circuitry 204 may include one or more baseband processors and/or control logic to process baseband signals received from a receive signal path of the RF circuitry 206 and to generate baseband signals for a transmit signal path of the RF circuitry 206. Baseband processing circuity 204 may interface with the application circuitry 202 for generation and processing of the baseband signals and for controlling operations of the RF circuitry 206. For example, in some embodiments, the baseband circuitry 204 may include a second generation (2G) baseband processor 204a, third generation (3G) baseband processor 204b, fourth generation (4G) baseband processor 204c, and/or other baseband processor(s) 204d for other existing generations, generations in development or to be developed in the future (e.g., fifth generation (5G), 6G, etc.). The baseband circuitry 204 (e.g., one or more of baseband processors 204a-d) may handle various radio control functions that enable communication with one or more radio networks via the RF circuitry 206. The radio control functions may include, but are not limited to, signal modulation/demodulation, encoding/decoding, radio frequency shifting, etc. In some embodiments, modulation/demodulation circuitry of the baseband circuitry 204 may include Fast-Fourier Transform (FFT), precoding, and/or constellation mapping/demapping functionality. In some embodiments, encoding/decoding circuitry of the baseband circuitry 204 may include convolution, tail-biting convolution, turbo, Viterbi, and/or Low Density Parity Check (LDPC) encoder/decoder functionality. Embodiments of modulation/demodulation and encoder/decoder functionality are not limited to these examples and may include other suitable functionality in other embodiments. [0030] In some embodiments, the baseband circuitry 204 may include elements of a protocol stack such as, for example, elements of an evolved universal terrestrial radio access network (EUTRAN) protocol including, for example, physical (PHY), media access control (MAC), radio link control (RLC), packet data convergence protocol (PDCP), and/or radio resource control (RRC) elements. A central processing unit (CPU) 204e of the baseband circuitry 204 may be configured to run elements of the protocol stack for signaling of the PHY, MAC, RLC, PDCP and/or RRC layers. In some embodiments, the baseband circuitry may include one or more audio digital signal processor(s) (DSP) 204f. The audio DSP(s) 204f may be include elements for compression/decompression and echo cancellation and may include other suitable processing elements in other embodiments. Components of the baseband circuitry may be suitably combined in a single chip, a single chipset, or disposed on a same circuit board in some embodiments. In some embodiments, some or all of the constituent components of the baseband circuitry 204 and the application circuitry 202 may be implemented together such as, for example, on a system on a chip (SOC).

[0031] In some embodiments, the baseband circuitry 204 may provide for communication compatible with one or more radio technologies. For example, in some embodiments, the baseband circuitry 204 may support communication with an evolved universal terrestrial radio access network (EUTRAN) and/or other wireless metropolitan area networks (WMAN), a wireless local area network (WLAN), a wireless personal area network (WPAN). Embodiments in which the baseband circuitry 204 is configured to support radio communications of more than one wireless protocol may be referred to as multi-mode baseband circuitry.

[0032] RF circuitry 206 may enable communication with wireless networks using modulated electromagnetic radiation through a non-solid medium. In various embodiments, the RF circuitry 206 may include switches, filters, amplifiers, etc. to facilitate the communication with the wireless network. RF circuitry 206 may include a receive signal path which may include circuitry to down-convert RF signals received from the FEM circuitry 208 and provide baseband signals to the baseband circuitry 204. RF circuitry 206 may also include a transmit signal path which may include circuitry to up-convert baseband signals provided by the baseband circuitry 204 and provide RF output signals to the FEM circuitry 208 for transmission.

[0033] In some embodiments, the RF circuitry 206 may include a receive signal path and a transmit signal path. The receive signal path of the RF circuitry 206 may include mixer circuitry 206a, amplifier circuitry 206b and filter circuitry 206c. The transmit signal path of the RF circuitry 206 may include filter circuitry 206c and mixer circuitry 206a. RF circuitry 206 may also include synthesizer circuitry 206d for synthesizing a frequency for use by the mixer circuitry 206a of the receive signal path and the transmit signal path. In some embodiments, the mixer circuitry 206a of the receive signal path may be configured to down-convert RF signals received from the FEM circuitry 208 based on the synthesized frequency provided by synthesizer circuitry 206d. The amplifier circuitry 206b may be configured to amplify the down-converted signals and the filter circuitry 206c may be a low-pass filter (LPF) or band-pass filter (BPF) configured to remove unwanted signals from the down-converted signals to generate output baseband signals. Output baseband signals may be provided to the baseband circuitry 204 for further processing. In some embodiments, the output baseband signals may be zero-frequency baseband signals, although this is not a requirement. In some embodiments, mixer circuitry 206a of the receive signal path may comprise passive mixers, although the scope of the embodiments is not limited in this respect.

[0034] In some embodiments, the mixer circuitry 206a of the transmit signal path may be configured to up-convert input baseband signals based on the synthesized frequency provided by the synthesizer circuitry 206d to generate RF output signals for the FEM circuitry 208. The baseband signals may be provided by the baseband circuitry 204 and may be filtered by filter circuitry 206c. The filter circuitry 206c may include a low-pass filter (LPF), although the scope of the embodiments is not limited in this respect.

[0035] In some embodiments, the mixer circuitry 206a of the receive signal path and the mixer circuitry 206a of the transmit signal path may include two or more mixers and may be arranged for quadrature downconversion and/or upconversion respectively. In some embodiments, the mixer circuitry 206a of the receive signal path and the mixer circuitry 206a of the transmit signal path may include two or more mixers and may be arranged for image rejection (e.g., Hartley image rejection). In some embodiments, the mixer circuitry 206a of the receive signal path and the mixer circuitry 206a may be arranged for direct downconversion and/or direct upconversion, respectively. In some embodiments, the mixer circuitry 206a of the receive signal path and the mixer circuitry 206a of the transmit signal path may be configured for super-heterodyne operation.

[0036] In some embodiments, the output baseband signals and the input baseband signals may be analog baseband signals, although the scope of the embodiments is not limited in this respect. In some alternate embodiments, the output baseband signals and the input baseband signals may be digital baseband signals. In these alternate embodiments, the RF circuitry 206 may include analog- to-digital converter (ADC) and digital-to-analog converter (DAC) circuitry and the baseband circuitry 204 may include a digital baseband interface to communicate with the RF circuitry 206.

[0037] In some dual -mode embodiments, a separate radio IC circuitry may be provided for processing signals for each spectrum, although the scope of the embodiments is not limited in this respect.

[0038] In some embodiments, the synthesizer circuitry 206d may be a fractional -N synthesizer or a fractional N/N+1 synthesizer, although the scope of the embodiments is not limited in this respect as other types of frequency synthesizers may be suitable. For example, synthesizer circuitry 206d may be a delta-sigma synthesizer, a frequency multiplier, or a synthesizer comprising a phase-locked loop with a frequency divider.

[0039] The synthesizer circuitry 206d may be configured to synthesize an output frequency for use by the mixer circuitry 206a of the RF circuitry 206 based on a frequency input and a divider control input. In some embodiments, the synthesizer circuitry 206d may be a fractional N/N+1 synthesizer.

[0040] In some embodiments, frequency input may be provided by a voltage controlled oscillator (VCO), although that is not a requirement. Divider control input may be provided by either the baseband circuitry 204 or the applications processor 202 depending on the desired output frequency. In some embodiments, a divider control input (e.g., N) may be determined from a look-up table based on a channel indicated by the applications processor 202. [0041] Synthesizer circuitry 206d of the RF circuitry 206 may include a divider, a delay-locked loop (DLL), a multiplexer and a phase accumulator. In some embodiments, the divider may be a dual modulus divider (DMD) and the phase accumulator may be a digital phase accumulator (DPA). In some embodiments, the DMD may be configured to divide the input signal by either N or N+l (e.g., based on a carry out) to provide a fractional division ratio. In some example embodiments, the DLL may include a set of cascaded, tunable, delay elements, a phase detector, a charge pump and a D-type flip-flop. In these embodiments, the delay elements may be configured to break a VCO period up into Nd equal packets of phase, where Nd is the number of delay elements in the delay line. In this way, the DLL provides negative feedback to help ensure that the total delay through the delay line is one VCO cycle.

[0042] In some embodiments, synthesizer circuitry 206d may be configured to generate a carrier frequency as the output frequency, while in other embodiments, the output frequency may be a multiple of the carrier frequency (e.g., twice the carrier frequency, four times the carrier frequency) and used in conjunction with quadrature generator and divider circuitry to generate multiple signals at the carrier frequency with multiple different phases with respect to each other. In some embodiments, the output frequency may be a LO frequency (fLO). In some embodiments, the RF circuitry 206 may include an IQ/polar converter. In some embodiments, the RF circuitry 206 may include a ΜΊΜΟ transceiver.

[0043] FEM circuitry 208 may include a receive signal path which may include circuitry configured to operate on RF signals received from one or more antennas 210, amplify the received signals and provide the amplified versions of the received signals to the RF circuitry 206 for further processing. FEM circuitry 208 may also include a transmit signal path which may include circuitry configured to amplify signals for transmission provided by the RF circuitry 206 for transmission by one or more of the one or more antennas 210.

[0044] In some embodiments, the FEM circuitry 208 may include a TX/RX switch to switch between transmit mode and receive mode operation. The FEM circuitry may include a receive signal path and a transmit signal path. The receive signal path of the FEM circuitry may include a low-noise amplifier (LNA) to amplify received RF signals and provide the amplified received RF signals as an output (e.g., to the RF circuitry 206). The transmit signal path of the FEM circuitry 208 may include a power amplifier (PA) to amplify input RF signals (e.g., provided by RF circuitry 206), and one or more filters to generate RF signals for subsequent transmission (e.g., by one or more of the one or more antennas 210.

[0045] In some embodiments, the UE device 200 may include additional elements such as, for example, memory/storage, display, camera, sensor, and/or input/output (I/O) interface.

[0046] In operation, the UE device 200 may communicate over both licensed spectrum and unlicensed spectrum (e.g., via the baseband circuitry 204, the RF circuitry 206, and the FEM circuitry 208). In some examples, the UE device 200 may support contemporaneous transmission over the licensed spectrum (e.g., PCell) and the unlicensed spectrum (e.g., SCell) For communication over the PCell and the SCell, the UE device 200 may use a self- contained frame structure in which control signaling and data may be transmitted with a single subframe in a time-division multiplexing (TDM) manner. For example, there may be two types of frame structure: one for downlink data transmission and another for uplink data transmission. To help support frequency- selective scheduling of transmissions (e.g., assigning specific frequency bands to respective UEs), initial MCS selection, power control, etc., the UE device 200 may receive (e.g., via the FEM circuitry 208) a request from an eNodeB to transmit a SRS signal. The request may be a UE-specific request received via DCI, or may pertain to a group of UEs via request received as part of group DCI, with the UE device 200 being assigned an exclusive resource for the SRS (e.g., a subset of subcarriers or a time window). Because of implementation of LBT in the unlicensed spectrum, the SRS transmissions may not be guaranteed as configured by eNodeB, which may negatively affect performance of uplink (UL) scheduling for the UE device 200. It is understood that the LBT procedure and SRS transmissions are performed by at least a combination of the baseband circuitry 204, the RF circuitry 206, and the FEM circuitry 208.

[0047] In one embodiment to support SRS transmission in the unlicensed spectrum, the UE device 200 may perform a modified LBT procedure. In some examples, the eNodeB may indicate to the UE device 200 in an SRS triggering message a type of LBT to be used for the SRS transmission. In one example, in response to a request from the eNodeB, the UE device 200may transmit the SRS without performing the LBT procedure. For example, if the SRS transmission occurs less than preconfigured time threshold (e.g., 16 μβ) after a downlink (DL) transmission, the LBT may be skipped. Additionally, even if the SRS transmission occurs outside of the preconfigured time threshold, because the SRS may only possess a very small portion of airtime (e.g., 1.4% of an unlicensed band in a case of a wideband SRS for 32 UEs with a 10ms periodicity), skipping the LBT procedure may have a small likelihood of interfering with other communications in the unlicensed spectrum.

[0048] In another example of a modified LBT procedure, the UE device

200 may employ a single interval LBT procedure, where if a CCA is made after a single time interval, the SRS signal is transmitted. The single time interval may be 25 μβ, in some examples. If no CCA is made, then the SRS transmission is aborted. In some examples, the one shot LBT may be used for aperiodic SRS transmissions (e.g., requested by the eNodeB) without a physical uplink shared channel (PUSCH) within existing mean channel open time (MCOT).

[0049] In yet another example of a modified LBT procedure, the UE device 200 may employ a LBT with random backoff procedure. In the LBT with random backoff procedure, the UE device 200 may determine a random LBT count and a contention window size (CWS). The UE device 200 may monitor a channel for the contention window timeframe, and then perform a CCA. If a CCA is made, the LBT count is decremented, and the process is repeated. So long as the CCA is made after each iteration, the process continues until the LBT count is zero. Once the LBT count is equal to zero, the SRS transmission is made. If the CCA is not made after any one of the iterations before the LBT count is equal to zero, then the process starts over. The LBT count may be any number from 3 to 7, in some examples. In some examples, the CWS may be fixed, such as 9 μβ. In other examples, the CWS may be variable. One of skill in the art will appreciate that, instead of decrementing a counter, a counter may be incremented until it reaches a random backoff count as part of the LBT with random backoff procedure.

[0050] In another embodiment to support SRS transmission in the unlicensed spectrum, the UE device 200 may multiplex SRS transmissions with other UEs by transmitting the SRS over a subset of subcarriers in the designated frequency band. In some examples in LTE, a default subcarrier repetition factor (RPF) for SRS transmission in an unlicensed band for the UE device 200 may multiplex SRS transmissions with other UEs by transmitting the SRS over a subset of subcarriers in the designated frequency band, may be set to 2 (e.g., every other sub-carrier). To allow more UEs to multiplex their SRSs, the RPF may be increased to an integer N. For example, in a current LTE implementation, 16 UEs may be multiplexed in a single SRS procedure. If the RPF is increased to 4, then 32 UEs may be supported in a single SRS procedure.

[0051] In another embodiment to support SRS transmission in the unlicensed spectrum, the UE device 200may transmit the SRS with or without a PUSCH. Typically in LTE, the UE device 200may only transmit the SRS in a last symbol period of a configured/designated subframe. Thus, if the UE device 200 transmits SRS only, then it may have to wait until the last symbol of the designated subframe for SRS transmission. This may cause the misalignment of the start/end of LBT of UEs or the UE has to wait for some time, e.g., until the last symbol, after finishing the LBT in the beginning of the subframe. To mitigate the timing issues, the UE device 200 may have an option configuration where the SRS symbol position is moved to a first symbol of the designated subframe, in addition to the existing configuration for SRS symbol position to be the last symbol. The signaling can be done via, for example, layer one or layer 2 (L1/L2) signaling such as an enhanced physical downlink control channel (E-PDCCH), a MAC control element (CE), a radio resource control (RRC) signaling, or other higher layer signaling.

[0052] In another embodiment to support SRS transmission in the unlicensed spectrum, the UE device 200 may interrupt (e.g., puncture) a downlink (DL) transmission burst to transmit a preconfigured SRS transmission. Interrupting the DL burst by the UE device 200 may be available in unlicensed spectrum due to uncertainty in channel access opportunities and UL/DL configuration in frame structure Type 3. The UE device 200 may consider each subframe as empty if no transmission in detected in that subframe. The detection may be accomplished via a method such as carrier routing system (CRS) presence detection. The interruption of the DL burst by the UE device 200 may increase SRS transmission opportunities. It is appreciated that transitioning a radio of the UE device 200 from DL to UL takes some time. Therefore, in some examples the interruption of the DL burst may also include interruption of one or more symbols before and after a symbol assigned for SRS transmission to allow radio turnaround time. In other examples, the UE 104 may shorten a time duration of an SRS signal by reducing the fast Fourier Transform (FFT) size of the transmission. For example, if the UE device 200 reduces the FFT size by half, the SRS symbol duration may also be halved. The duration for SRS transmission, or equivalently the FFT size for SRS, may be signaled via L1/L2 signaling, such as E-PDCCH, MAC CE, RRC signaling, or other higher layer signaling.

[0053] By using modified LBT, changing the repetition factor, or interrupting a DL burst, support for SRS transmissions in the unlicensed spectrum may mitigate uncertainty caused by the LBT procedure. The SRS transmitted by the UE 104 may be a wideband SRS or a narrowband SRS. In an example, based on the SRS provided by the UE device 200, the UE device 200 may receive, via a PDCCH, an UL grant that includes assigned UL resources.

[0054] FIG. 3 illustrates a flow diagram of a method 300 for a single interval LBT procedure for transmission of SRS in an unlicensed spectrum in accordance with some embodiments of the disclosure. The method 300 may be implemented in the UE 104 of FIG. 1, the UE device 200 of Figure 2, or combinations thereof.

[0055] The method 300 may include determining whether to transmit a

SRS transmission, at 310. In some examples, the determination as to whether the UE is to transmit a SRS is based on a received request to transmit a SRS from an eNodeB (e.g., the eNodeB 120 of FIG. 1). The request may be received via DCI. If the determination not to transmit a SRS, the method 300 may further include remaining idle, at 314.

[0056] The method 300 may further include monitoring a channel for communication for a single interval time window, at 320. The single time interval time window may be 25 μβ, in some examples. The method 300 may further include determining whether the channel is clear (e.g., performing a CCA), at 330. If the channel is clear, the method 300 may further include transmitting the SRS, at 340. Otherwise (e.g., if the channel is not clear), the method 300 may further include aborting transmission of the SRS, at 350. In some examples, the single interval LBT may be used for aperiodic SRS transmissions (e.g., requested by the eNodeB) without a physical uplink shared channel (PUSCH) within existing mean channel open time (MCOT).

[0057] FIG. 4 illustrates a flow diagram of a method 400 for a LBT with random backoff procedure for transmission of SRS in an unlicensed spectrum in accordance with some embodiments of the disclosure. The method 400 may be implemented in the UE 104 of FIG. 1, the UE device 200 of Figure 2, or combinations thereof.

[0058] The method 400 may include determining whether to transmit a

SRS transmission, at 410. In some examples, the determination as to whether the UE is to transmit a SRS is based on a received request to transmit a SRS from an eNodeB (e.g., the eNodeB 120 of FIG. 1). The request may be received via DCI. If the determination not to transmit a SRS, the method 400 may further include remaining idle, at 414.

[0059] The method 400 may further include selecting a random backoff count, at 416. The random backoff count may be from a random number generator of a UE, or may be received via a signal from an eNodeB. The method 400 may further include monitoring a channel for communication for a contention window time, at 420. The CWS may be fixed or variable. In some examples, the CWS may be 9 μβ. The random back off count may be in a range including 3-7, in some examples. The method 300 may further include determining whether the channel is clear (e.g., performing a CCA), at 430. If the channel is not clear, the method 400 may further include selecting a new random backoff count, at 410. In other examples, rather than selecting a new random backoff count, the method 400 may include doubling the CWS and resetting the random backoff count, and monitoring the channel for communication for the now doubled contention window time.

[0060] If the channel is clear, the method 400 may further include decrementing a random backoff count, at 440. The method 400 may further include determining whether the random backoff count is equal to zero, at 450. If the count is not equal to zero, the method 400 may further include repeating steps 420, 430, 440, and 450. If the random backoff count is equal to zero, the method 400 may further include transmitting the SRS, at 460.

[0061] FIG. 7 illustrates a flow diagram of a method 700 to transmit a sounding reference signal (SRS) in unlicensed spectrum in accordance with some embodiments of the disclosure. The method 700 may be implemented in the UE 104 of FIG. 1, the UE device 200 of Figure 2, or combinations thereof.

[0062] The method 700 may include receiving a request for transmission of the SRS in unlicensed spectrum, at 710. The transmission may be facilitated via license-assisted access (LAA).

[0063] In some examples, the method 700 may further include transmitting the SRS without performing the LBT procedure. In some examples, the method 700 may further include performing a modified listen-bef ore-talk (LBT) procedure. In some examples, performance of the modified LBT may include monitoring a channel of the unlicensed spectrum for a single interval window. In response to the CCA after monitoring the channel of the unlicensed spectrum for the single interval window, transmitting the SRS, and in response to lack of the CCA after monitoring the channel of the unlicensed spectrum for the single interval window, aborting transmission of the SRS. In some examples, the single interval window is equal to 25 μβ.

[0064] In some examples, performance of the modified LBT may include selecting a random backoff count, and, for a count of iterations based on the random backoff count, monitoring a channel of the unlicensed spectrum for a contention window time, and in response to a CCA after monitoring the channel of the unlicensed spectrum for the contention window time, decrementing the random backoff count. In some examples, the method 700 may include receiving the random backoff count from an evolved node B (eNodeB). The random backoff count may be in a range of 3 to 7. In some examples, the contention window time may be equal to 9 μβ. In some examples, the contention window time may be variable. In response to completion of the count of iterations, the method 700 may include transmitting the SRS. In some examples for the count of iterations based on the random backoff count, in response to lack of the CCA after monitoring the channel of the unlicensed spectrum for the contention window time, the method 700 may include restarting the count of iterations. In some examples for the count of iterations based on the random backoff count, in response to lack of the CCA after monitoring the channel of the unlicensed spectrum for the contention window time, the method 700 may further include doubling the contention window time, and restarting the count of iterations. In some examples for the count of iterations based on the random backoff count, in response to lack of the CCA after monitoring the channel of the unlicensed spectrum for the contention window time, the method 700 may further include reselecting the random backoff count, and restarting the count of iterations.

[0065] The method 700 may further include, in response to the request for transmission of the SRS, encode the SRS for transmission in the unlicensed spectrum, at 720. In some examples, the transmission of the SRS may be further in response to a clear channel assessment (CCA) made as part of the modified LBT procedure. In some examples, transmission of the SRS may include repeating transmission of a narrowband SRS across a subset of subcarriers of the unlicensed spectrum based on a repetition factor. In some examples, the repetition factor may be greater than two. In some examples, the method 700 may include receiving subcarrier resource allocation for transmission of the SRS via downlink control information (DCI) from an evolved node B (eNodeB). In some examples, transmission of the SRS may include transmitting the SRS at a first symbol period of a designated subframe. In some examples, transmission of the SRS may include interrupting a downlink burst to transmit the SRS. IN some examples, the method 700 may include prior to the transmission of the SRS, halving the fast Fourier transform size for the SRS to reduce a SRS transmission duration. The method 700 may further include decoding an UL grant, received via a PDCCH, that includes assigned UL resources, wherein the assigned UL resources are based on the SRS

[0066] FIG. 8 illustrates a flow diagram of a method 800 to request a sounding reference signal (SRS) in unlicensed spectrum in accordance with some embodiments of the disclosure. The method 600 may be implemented in any of the eNodeB 120 of Figure 1.

[0067] The method 800 may include providing a request for transmission of the SRS in unlicensed spectrum to a user equipment (UE), at 810. Transmission may be facilitated via license-assisted access (LAA). The UE may include the UE 104 of FIG. 1, the UE device 200 of FIG. 2, or combinations thereof. In some examples, provision of the request for transmission of the UE may include providing the request for the SRS in downlink control information (DCI). In some examples, provision of the request for transmission of the UE may include providing a subset of subcarriers of the unlicensed spectrum on which to transmit the SRS. In some examples, provision of the request for transmission of the UE may include providing a repetition factor for frequency of repetition across subcarriers. In some examples, provision of the request for transmission of the UE may include providing a modified listen-before-talk (LBT) procedure type to be used by the UE prior to transmission of the SRS. The modified LBT procedure type may include one of no LBT, single interval LBT, or LBT with random backoff, as previously described. In some examples, provision of the request for transmission of the UE may include providing a request to provide the SRS in a first symbol period of a configured subframe. In some examples, provision of the request for transmission of the UE may include providing a request to provide the request for transmission of the SRS in unlicensed spectrum to a plurality of UEs. The request may include respective resource allocation for each of the plurality of UEs.

[0068] The method 800 may further include receiving the SRS transmission from the UE in the unlicensed spectrum, at 820. In some examples, reception of the SRS transmission from the UE in the unlicensed spectrum may include receiving the SRS in a middle of a downlink burst transmission to the UE. The method 800 may further include scheduling a frequency band in the unlicensed spectrum for the UE based on the SRS transmission, at 830. The method 800 may further include increasing a repetition factor to a new value to provide an increased count of available SRS transmissions slots. The method 800 may further include encode a request for a narrow band SRS transmission to a plurality of user equipments (UEs) that includes the UE, wherein a maximum count of the plurality of UEs is based on the repetition factor. The repetition factor may be greater than two.

[0069] FIG. 9 illustrates generally an example of a block diagram of a machine 900 upon which any one or more of the techniques (e.g., methodologies) discussed herein can perform in accordance with some embodiments. In alternative embodiments, the machine 900 can operate as a standalone device or can be connected (e.g., networked) to other machines. In a networked deployment, the machine 900 can operate in the capacity of a server machine, a client machine, or both in server-client network environments. In an example, the machine 900 can act as a peer machine in peer-to-peer (P2P) (or other distributed) network environment. The machine 900 can be a personal computer (PC), a tablet PC, a set-top box (STB), a personal digital assistant (PDA), a mobile telephone, a web appliance, a network router, switch or bridge, or any machine capable of executing instructions (sequential or otherwise) that specify actions to be taken by that machine. Further, while only a single machine is illustrated, the term "machine" shall also be taken to include any collection of machines that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methodologies discussed herein, such as cloud computing, software as a service (SaaS), other computer cluster configurations.

[0070] Examples, as described herein, can include, or can operate on, logic or a number of components, modules, or mechanisms. Modules are tangible entities (e.g., hardware) capable of performing specified operations when operating. A module includes hardware. In an example, the hardware can be specifically configured to carry out a specific operation (e.g., hardwired). In an example, the hardware can include configurable execution units (e.g., transistors, circuits, etc.) and a computer readable medium containing instructions, where the instructions configure the execution units to carry out a specific operation when in operation. The configuring can occur under the direction of the executions units or a loading mechanism. Accordingly, the execution units are communicatively coupled to the computer readable medium when the device is operating. In this example, the execution units can be a member of more than one module. For example, under operation, the execution units can be configured by a first set of instructions to implement a first module at one point in time and reconfigured by a second set of instructions to implement a second module.

[0071] Machine (e.g., computer system) 900 can include a hardware processor 902 (e.g., a central processing unit (CPU), a graphics processing unit (GPU), a hardware processor core, or any combination thereof), a main memory 904 and a static memory 906, some or all of which can communicate with each other via an interlink (e.g., bus) 908. The machine 900 can further include a display unit 910, an alphanumeric input device 912 (e.g., a keyboard), and a user interface (UI) navigation device 914 (e.g., a mouse). In an example, the display unit 910, alphanumeric input device 912 and UI navigation device 914 can be a touch screen display. The machine 900 can additionally include a storage device (e.g., drive unit) 916, a signal generation device 918 (e.g., a speaker), a network interface device 920, and one or more sensors 921, such as a global positioning system (GPS) sensor, compass, accelerometer, or other sensor. The machine 900 can include an output controller 928, such as a serial (e.g., universal serial bus (USB), parallel, or other wired or wireless (e.g., infrared (IR), near field communication (NFC), etc.) connection to communicate or control one or more peripheral devices (e.g., a printer, card reader, etc.).

[0072] The storage device 916 can include a machine readable medium

922 that is non-transitory on which is stored one or more sets of data structures or instructions 924 (e.g., software) embodying or utilized by any one or more of the techniques or functions described herein. The instructions 924 can also reside, completely or at least partially, within the main memory 904, within static memory 906, or within the hardware processor 902 during execution thereof by the machine 900. In an example, one or any combination of the hardware processor 902, the main memory 904, the static memory 906, or the storage device 916 can constitute machine readable media.

[0073] While the machine readable medium 922 is illustrated as a single medium, the term "machine readable medium" can include a single medium or multiple media (e.g., a centralized or distributed database, and/or associated caches and servers) configured to store the one or more instructions 924.

[0074] The term "machine readable medium" can include any medium that is capable of storing, encoding, or carrying instructions for execution by the machine 900 and that cause the machine 900 to perform any one or more of the techniques of the present disclosure, or that is capable of storing, encoding or carrying data structures used by or associated with such instructions. Non-limiting machine readable medium examples can include solid-state memories, and optical and magnetic media. In an example, a massed machine readable medium comprises a machine readable medium with a plurality of particles having invariant (e.g., rest) mass. Accordingly, massed machine-readable media are not transitory propagating signals. Specific examples of massed machine readable media can include: non-volatile memory, such as semiconductor memory devices (e.g., Electrically Programmable Read-Only Memory (EPROM), Electrically Erasable Programmable Read-Only Memory (EEPROM)) and flash memory devices; magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks.

[0075] The instructions 924 can further be transmitted or received over a communications network 926 using a transmission medium via the network interface device 920 utilizing any one of a number of transfer protocols (e.g., frame relay, internet protocol (IP), transmission control protocol (TCP), user datagram protocol (UDP), hypertext transfer protocol (HTTP), etc.). Example communication networks can include a local area network (LAN), a wide area network (WAN), a packet data network (e.g., the Internet), mobile telephone networks (e.g., cellular networks), Plain Old Telephone (POTS) networks, and wireless data networks (e.g., Institute of Electrical and Electronics Engineers (IEEE) 802.11 family of standards known as Wi-Fi®, IEEE 802.16 family of standards known as WiMax®), IEEE 802.15.4 family of standards, peer-to-peer (P2P) networks, among others. In an example, the network interface device 920 can include one or more physical jacks (e.g., Ethernet, coaxial, or phone jacks) or one or more antennas to connect to the communications network 926. In an example, the network interface device 920 can include a plurality of antennas to wirelessly communicate using at least one of single-input multiple-output (SFMO), multiple-input multiple-output (MFMO), or multiple-input single-output (MISO) techniques. The term "transmission medium" shall be taken to include any intangible medium that is capable of storing, encoding or carrying instructions for execution by the machine 900, and includes digital or analog communications signals or other intangible medium to facilitate communication of such software.

[0076] As used herein, the term "circuitry" may refer to, be part of, or include an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group), and/or memory (shared, dedicated, or group) that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable hardware components that provide the described functionality. In some embodiments, the circuitry may be implemented in, or functions associated with the circuitry may be implemented by, one or more software or firmware modules. In some embodiments, circuitry may include logic, at least partially operable in hardware. [0077] Additional Notes & Examples:

[0078] Example 1 is an apparatus of User Equipment (UE), the apparatus comprising: memory; and processing circuitry, the processing circuitry to:

decode a request for transmission of a sounding reference signal (SRS) in unlicensed spectrum, wherein transmission is facilitated via license-assisted access (LAA); perform a modified listen-before-talk (LBT) procedure; in response to a clear channel assessment (CCA) made as part of the modified LBT procedure, encode the SRS for transmission; and decode an uplink (UL) grant, received via a physical downlink control channel (PDCCH), that includes assigned UL resources, wherein the assigned UL resources are based on the SRS.

[0079] In Example 2, the subject matter of Example 1 optionally includes wherein to perform the modified LBT procedure, the processing circuitry to: monitor a channel of the unlicensed spectrum for a single interval window; in response to the CCA after monitoring the channel of the unlicensed spectrum for the single interval window, encode the SRS for transmission; and in response to lack of the CCA after monitoring the channel of the unlicensed spectrum for the single interval window, abort transmission of the SRS.

[0080] In Example 3, the subject matter of Example 2 optionally includes wherein the single interval window is equal to 25 μβ.

[0081] In Example 4, the subject matter of any one or more of Examples

1-3 optionally include wherein to perform the modified LBT procedure, the processing circuitry to: select a random backoff count; for a count of iterations based on the random backoff count: monitor a channel of the unlicensed spectrum for a contention window time; and in response to a CCA after monitoring the channel of the unlicensed spectrum for the contention window time, decrement the random backoff count; and in response to completion of the count of iterations, encode the SRS for transmission. [0082] In Example 5, the subject matter of Example 4 optionally includes wherein for the count of iterations based on the random backoff count, the processing circuitry to, in response to lack of the CCA after monitoring the channel of the unlicensed spectrum for the contention window time, restart the count of iterations.

[0083] In Example 6, the subject matter of any one or more of Examples

4-5 optionally include wherein for the count of iterations based on the random backoff count, the processing circuitry to, in response to lack of the CCA after monitoring the channel of the unlicensed spectrum for the contention window time: double the contention window time; and restart the count of iterations.

[0084] In Example 7, the subject matter of any one or more of Examples

4-6 optionally include wherein for the count of iterations based on the random backoff count, the processing circuitry to, in response to lack of the CCA after monitoring the channel of the unlicensed spectrum for the contention window time: reselect a random backoff count; and restart the count of iterations.

[0085] In Example 8, the subject matter of any one or more of Examples

4-7 optionally include wherein the random backoff count is in a range of 3 to 7.

[0086] In Example 9, the subject matter of any one or more of Examples

4-8 optionally include wherein the contention window time is equal to 9 μβ.

[0087] In Example 10, the subject matter of any one or more of

Examples 4-9 optionally include wherein the contention window time is variable.

[0088] In Example 11, the subject matter of any one or more of

Examples 1-10 optionally include wherein to select the random backoff count includes the processing circuitry to receive the random backoff count from an evolved node B (eNodeB).

[0089] In Example 12, the subject matter of any one or more of

Examples 1-11 optionally include front-end module circuitry to repeat transmission of the SRS across a subset of subcarriers of the unlicensed spectrum based on a repetition factor.

[0090] In Example 13, the subject matter of Example 12 optionally includes wherein the repetition factor is greater than two. [0091] In Example 14, the subject matter of any one or more of

Examples 12-13 optionally include wherein the processing circuitry further to receive subcarrier resource allocation for transmission of the SRS via downlink control information from an evolved node B.

[0092] In Example 15, the subject matter of any one or more of

Examples 1-14 optionally include wherein to encode the SRS for transmission includes the processing circuitry to transmit the SRS at a first symbol period of a designated subframe.

[0093] In Example 16, the subject matter of any one or more of

Examples 1-15 optionally include wherein to encode the SRS for transmission includes the processing circuitry to interrupt a downlink burst to transmit the SRS.

[0094] In Example 17, the subject matter of Example 16 optionally includes wherein to encode the SRS for transmission includes the processing circuitry to halve the fast Fourier transform size for the SRS to reduce a SRS transmission duration.

[0095] Example 18 is an apparatus of evolved Node B (eNodeB), the apparatus comprising: memory; and processing circuitry, the processing circuitry to: encode a request for transmission of a sounding reference signal (SRS) in unlicensed spectrum to a user equipment (UE), wherein transmission is facilitated via license-assisted access (LAA), wherein the request for the SRS is included in downlink control information (DCI); decode the SRS transmission received from the UE in the unlicensed spectrum; and schedule a frequency band in the unlicensed spectrum for the UE based on the SRS transmission.

[0096] In Example 19, the subject matter of Example 18 optionally includes wherein to encode the request for transmission of the SRS in unlicensed spectrum to the UE includes the processing circuitry to provide a narrowband SRS request that includes a subset of subcarriers of the unlicensed spectrum on which to transmit the SRS.

[0097] In Example 20, the subject matter of Example 19 optionally includes wherein to encode the request for transmission of the SRS in unlicensed spectrum to the UE includes the processing circuitry to provide a repetition factor for frequency of repetition across subcarriers. [0098] In Example 21, the subject matter of any one or more of

Examples 18-20 optionally include wherein to encode the request for transmission of the SRS in unlicensed spectrum to the UE includes the processing circuitry to encode a modified listen-bef ore-talk (LBT) procedure type to be used by the UE prior to transmission of the SRS.

[0099] In Example 22, the subject matter of Example 21 optionally includes wherein the modified LBT procedure type includes one of no LBT, single interval LBT, or LBT with random backoff.

[00100] In Example 23, the subject matter of any one or more of

Examples 18-22 optionally include wherein to encode the request for transmission of the SRS in unlicensed spectrum to the UE includes the processing circuitry to encode a request to provide the SRS in a first symbol period of a configured subframe.

[00101] In Example 24, the subject matter of any one or more of

Examples 18-23 optionally include wherein to encode the request for transmission of the SRS in unlicensed spectrum to the UE includes the processing circuitry to encode a request to provide the request for transmission of the SRS in unlicensed spectrum to a plurality of UEs, wherein the request includes respective resource allocation for each of the plurality of UEs.

[00102] In Example 25, the subject matter of any one or more of

Examples 18-24 optionally include wherein to decode the SRS transmission received from the UE in the unlicensed spectrum includes the processing circuitry to receive the SRS in a middle of a downlink burst transmission to the UE.

[00103] In Example 26, the subject matter of any one or more of

Examples 18-25 optionally include wherein to encode the request for transmission of the SRS includes the processing circuitry to: increase a repetition factor to a new value to provide an increased count of available SRS

transmissions slots; and encode a request for a narrow band SRS transmission to a plurality of user equipments (UEs) that includes the UE, wherein a maximum count of the plurality of UEs is based on the repetition factor.

[00104] In Example 27, the subject matter of Example 26 optionally includes wherein the repetition factor is greater than two. [00105] Example 28 is at least one machine-readable medium including instructions to transmit a sounding reference signal (SRS) in unlicensed spectrum, which when executed by a machine, cause the machine to: decode a request for transmission of the SRS in unlicensed spectrum, wherein

transmission is facilitated via license-assisted access (LAA); in response to the request for transmission of the SRS, encode the SRS for transmission in the unlicensed spectrum; and decode an uplink (UL) grant, received via a physical downlink control channel (PDCCH), that includes assigned UL resources, wherein the assigned UL resources are based on the SRS.

[00106] In Example 29, the subject matter of Example 28 optionally includes instructions, which when executed by a machine, cause the machine to transmit the SRS without performing the LBT procedure.

[00107] In Example 30, the subject matter of any one or more of

Examples 28-29 optionally include instructions, which when executed by a machine, cause the machine to perform a modified listen-before-talk (LBT) procedure; wherein the SRS is encoded for transmission further in response to a clear channel assessment (CCA) made as part of the modified LBT procedure.

[00108] In Example 31, the subject matter of Example 30 optionally includes wherein to perform the modified LBT procedure includes instructions, which when executed by a machine, cause the machine to: monitor a channel of the unlicensed spectrum for a single interval window; in response to the CCA after monitoring the channel of the unlicensed spectrum for the single interval window, encode the SRS for transmission; and in response to lack of the CCA after monitoring the channel of the unlicensed spectrum for the single interval window, abort transmission of the SRS.

[00109] In Example 32, the subject matter of Example 31 optionally includes wherein the single interval window is equal to 25 μβ.

[00110] In Example 33, the subject matter of any one or more of

Examples 30-32 optionally include wherein to perform the modified LBT procedure includes instructions, which when executed by a machine, cause the machine to: select a random backoff count; for a count of iterations based on the random backoff count: monitor a channel of the unlicensed spectrum for a contention window time; and in response to a CCA after monitoring the channel of the unlicensed spectrum for the contention window time, decrement the random backoff count; and in response to completion of the count of iterations, encode the SRS for transmission.

[00111] In Example 34, the subject matter of Example 33 optionally includes instructions, which when executed by a machine, cause the machine to, for the count of iterations based on the random backoff count, in response to lack of the CCA after monitoring the channel of the unlicensed spectrum for the contention window time, restart the count of iterations.

[00112] In Example 35, the subject matter of any one or more of

Examples 33-34 optionally include instructions, which when executed by a machine, cause the machine to, for the count of iterations based on the random backoff count, in response to lack of the CCA after monitoring the channel of the unlicensed spectrum for the contention window time: double the contention window time; and restart the count of iterations.

[00113] In Example 36, the subject matter of any one or more of

Examples 33-35 optionally include wherein for the count of iterations based on the random backoff count includes instructions, which when executed by a machine, cause the machine to, in response to lack of the CCA after monitoring the channel of the unlicensed spectrum for the contention window time: reselect the random backoff count; and restart the count of iterations.

[00114] In Example 37, the subject matter of any one or more of

Examples 33-36 optionally include wherein the random backoff count in a range of 3 to 7.

[00115] In Example 38, the subject matter of any one or more of

Examples 33-37 optionally include wherein the contention window time is equal

[00116] In Example 39, the subject matter of any one or more of

Examples 33-38 optionally include wherein the contention window time is variable.

[00117] In Example 40, the subject matter of any one or more of

Examples 33-39 optionally include wherein to select a random backoff count includes instructions, which when executed by a machine, cause the machine to receive the random backoff count from an evolved node B (eNodeB). [00118] In Example 41, the subject matter of any one or more of

Examples 28-40 optionally include wherein to encode the SRS for transmission includes instructions, which when executed by a machine, cause the machine to encode the SRS for repeat transmission across a subset of subcarriers of the unlicensed spectrum based on a repetition factor.

[00119] In Example 42, the subject matter of Example 41 optionally includes wherein the repetition factor is greater than two.

[00120] In Example 43, the subject matter of any one or more of

Examples 41-42 optionally include instructions, which when executed by a machine, cause the machine to receive subcarrier resource allocation for transmission of the SRS via downlink control information (DCI) from an evolved node B (eNodeB).

[00121] In Example 44, the subject matter of any one or more of

Examples 28-43 optionally include wherein to transmit the SRS includes instructions, which when executed by a machine, cause the machine to encode the SRS for transmission at a first symbol period of a designated subframe.

[00122] In Example 45, the subject matter of any one or more of

Examples 28-44 optionally include wherein to transmit the SRS includes instructions, which when executed by a machine, cause the machine to encode the SRS for transmission to interrupt a downlink burst.

[00123] In Example 46, the subject matter of Example 45 optionally includes instructions, which when executed by a machine, cause the machine to, prior to the encoding the SRS for transmission, halve the fast Fourier transform size for the SRS to reduce a SRS transmission duration.

[00124] Example 47 is at least one machine-readable medium including instructions to request a sounding reference signal (SRS) in unlicensed spectrum, which when executed by a machine, cause the machine to: encode a request for transmission of the SRS in unlicensed spectrum to a user equipment (UE), wherein transmission is facilitated via license-assisted access (LAA); decode the SRS transmission received from the UE in the unlicensed spectrum; and schedule a frequency band in the unlicensed spectrum for the UE based on the SRS transmission. [00125] In Example 48, the subject matter of Example 47 optionally includes wherein to encode the request for transmission of the SRS in unlicensed spectrum to the UE includes instructions, which when executed by a machine, cause the machine to encode the request for the SRS in downlink control information (DCI).

[00126] In Example 49, the subject matter of any one or more of

Examples 47-48 optionally include wherein to encode the request for transmission of the SRS in unlicensed spectrum to the UE includes instructions, which when executed by a machine, cause the machine to encode a subset of subcarriers of the unlicensed spectrum on which to transmit a narrowband SRS.

[00127] In Example 50, the subject matter of Example 49 optionally includes wherein to encode the request for transmission of the SRS in unlicensed spectrum to the UE includes instructions, which when executed by a machine, cause the machine to provide a repetition factor for frequency of repetition across subcarriers.

[00128] In Example 51, the subject matter of any one or more of

Examples 47-50 optionally include wherein to encode the request for transmission of the SRS in unlicensed spectrum to the UE includes instructions, which when executed by a machine, cause the machine to encode a modified listen-before-talk (LBT) procedure type to be used by the UE prior to transmission of the SRS.

[00129] In Example 52, the subject matter of Example 51 optionally includes wherein the modified LBT procedure type includes one of no LBT, single interval LBT, or LBT with random backoff.

[00130] In Example 53, the subject matter of any one or more of

Examples 47-52 optionally include wherein to encode the request for transmission of the SRS in unlicensed spectrum to the UE includes instructions, which when executed by a machine, cause the machine to encode a request to encode the SRS in a first symbol period of a configured subframe.

[00131] In Example 54, the subject matter of any one or more of

Examples 47-53 optionally include wherein to provide the request for transmission of the SRS in unlicensed spectrum to the UE includes instructions, which when executed by a machine, cause the machine to encode a request to provide the request for transmission of the SRS in unlicensed spectrum to a plurality of UEs, wherein the request includes respective resource allocation for each of the plurality of UEs.

[00132] In Example 55, the subject matter of any one or more of

Examples 47-54 optionally include wherein to receive the SRS transmission from the UE in the unlicensed spectrum includes instructions, which when executed by a machine, cause the machine to receive the SRS in a middle of a downlink burst transmission to the UE.

[00133] In Example 56, the subject matter of any one or more of

Examples 47-55 optionally include wherein to encode the request for transmission of the SRS includes instructions, which when executed by a machine, cause the machine to: increase a repetition factor to a new value to provide an increased count of available SRS transmissions slots; and encode a request for a narrow band SRS transmission to a plurality of user equipments (UEs) that includes the UE, wherein a maximum count of the plurality of UEs is based on the repetition factor.

[00134] In Example 57, the subject matter of Example 56 optionally includes wherein the repetition factor is greater than two.

[00135] Example 58 is an apparatus to transmit a sounding reference signal (SRS) in unlicensed spectrum, the apparatus comprising: means for decoding a request for transmission of the SRS in unlicensed spectrum, wherein transmission is facilitated via license-assisted access (LAA); in response to the request for transmission of the SRS, means for encoding the SRS for

transmission in the unlicensed spectrum; and means for decoding an uplink (UL) grant, received via a physical downlink control channel (PDCCH), that includes assigned UL resources, wherein the assigned UL resources are based on the SRS.

[00136] In Example 59, the subject matter of Example 58 optionally includes means for transmitting the SRS without performing the LBT procedure.

[00137] In Example 60, the subject matter of any one or more of

Examples 58-59 optionally include means for performing a modified listen- before-talk (LBT) procedure; wherein the SRS is encoded for transmission further in response to a clear channel assessment (CCA) made as part of the modified LBT procedure.

[00138] In Example 61, the subject matter of Example 60 optionally includes wherein means for performing the modified LBT procedure includes: means for monitoring a channel of the unlicensed spectrum for a single interval window; in response to the CCA after monitoring the channel of the unlicensed spectrum for the single interval window, means for encoding the SRS for transmission; and in response to lack of the CCA after monitoring the channel of the unlicensed spectrum for the single interval window, means for aborting transmission of the SRS.

[00139] In Example 62, the subject matter of Example 61 optionally includes wherein the single interval window is equal to 25 μβ.

[00140] In Example 63, the subject matter of any one or more of

Examples 60-62 optionally include wherein means for performing the modified LBT procedure includes: means for selecting a random backoff count; for a count of iterations based on the random backoff count: means for monitoring a channel of the unlicensed spectrum for a contention window time; and in response to a CCA after monitoring the channel of the unlicensed spectrum for the contention window time, means for decrementing the random backoff count; and in response to completion of the count of iterations, means for encoding the SRS for transmission.

[00141] In Example 64, the subject matter of Example 63 optionally includes for the count of iterations based on the random backoff count, in response to lack of the CCA after monitoring the channel of the unlicensed spectrum for the contention window time, means for restarting the count of iterations.

[00142] In Example 65, the subject matter of any one or more of

Examples 63-64 optionally include for the count of iterations based on the random backoff count, in response to lack of the CCA after monitoring the channel of the unlicensed spectrum for the contention window time: means for doubling the contention window time; and means for restarting the count of iterations. [00143] In Example 66, the subject matter of any one or more of

Examples 63-65 optionally include wherein for the count of iterations based on the random backoff count includes, in response to lack of the CCA after monitoring the channel of the unlicensed spectrum for the contention window time: means for reselecting the random backoff count; and means for restarting the count of iterations.

[00144] In Example 67, the subject matter of any one or more of

Examples 63-66 optionally include wherein the random backoff count in a range of 3 to 7.

[00145] In Example 68, the subject matter of any one or more of

Examples 63-67 optionally include wherein the contention window time is equal

[00146] In Example 69, the subject matter of any one or more of

Examples 63-68 optionally include wherein the contention window time is variable.

[00147] In Example 70, the subject matter of any one or more of

Examples 63-69 optionally include wherein to select a random backoff count includes receive the random backoff count from an evolved node B (eNodeB).

[00148] In Example 71, the subject matter of any one or more of

Examples 58-70 optionally include wherein means for encoding the SRS for transmission includes encoding the SRS for repeat transmission across a subset of subcarriers of the unlicensed spectrum based on a repetition factor.

[00149] In Example 72, the subject matter of Example 71 optionally includes wherein the repetition factor is greater than two.

[00150] In Example 73, the subject matter of any one or more of

Examples 71-72 optionally include means for receiving subcarrier resource allocation for transmission of the SRS via downlink control information (DCI) from an evolved node B (eNodeB).

[00151] In Example 74, the subject matter of any one or more of

Examples 58-73 optionally include wherein means for transmitting the SRS includes means for encoding the SRS for transmission at a first symbol period of a designated subframe. [00152] In Example 75, the subject matter of any one or more of

Examples 58-74 optionally include wherein means for transmitting the SRS includes encoding the SRS for transmission to interrupt a downlink burst.

[00153] In Example 76, the subject matter of Example 75 optionally includes prior to the encoding the SRS for transmission, means for halving the fast Fourier transform size for the SRS to reduce a SRS transmission duration.

[00154] Example 77 is an apparatus to request a sounding reference signal (SRS) in unlicensed spectrum, the apparatus comprising: means for encoding a request for transmission of the SRS in unlicensed spectrum to a user equipment (UE), wherein transmission is facilitated via license-assisted access (LAA); means for decoding the SRS transmission received from the UE in the unlicensed spectrum; and means for scheduling a frequency band in the unlicensed spectrum for the UE based on the SRS transmission.

[00155] In Example 78, the subject matter of Example 77 optionally includes wherein means for encoding the request for transmission of the SRS in unlicensed spectrum to the UE includes means for encoding the request for the SRS in downlink control information (DCI).

[00156] In Example 79, the subject matter of any one or more of

Examples 77-78 optionally include wherein means for encoding the request for transmission of the SRS in unlicensed spectrum to the UE includes means for encoding a subset of subcarriers of the unlicensed spectrum on which to transmit a narrowband SRS.

[00157] In Example 80, the subject matter of Example 79 optionally includes wherein means for encoding the request for transmission of the SRS in unlicensed spectrum to the UE includes means for providing a repetition factor for frequency of repetition across subcarriers.

[00158] In Example 81, the subject matter of any one or more of

Examples 77-80 optionally include wherein means for encoding the request for transmission of the SRS in unlicensed spectrum to the UE includes means for encoding a modified listen-before-talk (LBT) procedure type to be used by the UE prior to transmission of the SRS. [00159] In Example 82, the subject matter of Example 81 optionally includes wherein the modified LBT procedure type includes one of no LBT, single interval LBT, or LBT with random backoff.

[00160] In Example 83, the subject matter of any one or more of

Examples 77-82 optionally include wherein means for encoding the request for transmission of the SRS in unlicensed spectrum to the UE includes means for encoding a request to encoding the SRS in a first symbol period of a configured subframe.

[00161] In Example 84, the subject matter of any one or more of

Examples 77-83 optionally include wherein means for providing the request for transmission of the SRS in unlicensed spectrum to the UE includes means for encoding a request to provide the request for transmission of the SRS in unlicensed spectrum to a plurality of UEs, wherein the request includes respective resource allocation for each of the plurality of UEs.

[00162] In Example 85, the subject matter of any one or more of

Examples 77-84 optionally include wherein means for receiving the SRS transmission from the UE in the unlicensed spectrum includes receive the SRS in a middle of a downlink burst transmission to the UE.

[00163] In Example 86, the subject matter of any one or more of

Examples 77-85 optionally include wherein means for encoding the request for transmission of the SRS includes: means for increasing a repetition factor to a new value to provide an increased count of available SRS transmissions slots; and means for encoding a request for a narrow band SRS transmission to a plurality of user equipments (UEs) that includes the UE, wherein a maximum count of the plurality of UEs is based on the repetition factor.

[00164] In Example 87, the subject matter of Example 86 optionally includes wherein the repetition factor is greater than two.

[00165] The above detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments that may be practiced. These embodiments are also referred to herein as "examples." Such examples may include elements in addition to those shown or described. However, also contemplated are examples that include the elements shown or described. Moreover, also contemplate are examples using any combination or permutation of those elements shown or described (or one or more aspects thereof), either with respect to a particular example (or one or more aspects thereof), or with respect to other examples (or one or more aspects thereof) shown or described herein.

[00166] Publications, patents, and patent documents referred to in this document are incorporated by reference herein in their entirety, as though individually incorporated by reference. In the event of inconsistent usages between this document and those documents so incorporated by reference, the usage in the incorporated reference(s) are supplementary to that of this document; for irreconcilable inconsistencies, the usage in this document controls.

[00167] In this document, the terms "a" or "an" are used, as is common in patent documents, to include one or more than one, independent of any other instances or usages of "at least one" or "one or more." In this document, the term "or" is used to refer to a nonexclusive or, such that "A or B" includes "A but not B," "B but not A," and "A and B," unless otherwise indicated. In the appended claims, the terms "including" and "in which" are used as the plain-English equivalents of the respective terms "comprising" and "wherein." Also, in the following claims, the terms "including" and "comprising" are open-ended, that is, a system, device, article, or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. Moreover, in the following claims, the terms "first," "second," and "third," etc. are used merely as labels, and are not intended to suggest a numerical order for their objects.

[00168] The above description is intended to be illustrative, and not restrictive. For example, the above-described examples (or one or more aspects thereof) may be used in combination with others. Other embodiments may be used, such as by one of ordinary skill in the art upon reviewing the above description. The Abstract is to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Also, in the above Detailed Description, various features may be grouped together to streamline the disclosure. However, the claims may not set forth features disclosed herein because embodiments may include a subset of said features. Further, embodiments may include fewer features than those disclosed in a particular example. Thus, the following claims are hereby incorporated into the Detailed Description, with a claim standing on its own as a separate embodiment. The scope of the embodiments disclosed herein is to be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

Claims

CLAIMS What is claimed is:

1. An apparatus of User Equipment (UE), the apparatus comprising:

memory; and processing circuitry, the processing circuitry to:

decode a request for transmission of a sounding reference signal (SRS) in unlicensed spectrum, wherein transmission is facilitated via license- assisted access (LAA);

perform a modified listen-before-talk (LBT) procedure;

in response to a clear channel assessment (CCA) made as part of the modified LBT procedure, encode the SRS for transmission; and

decode an uplink (UL) grant, received via a physical downlink control channel (PDCCH), that includes assigned UL resources, wherein the assigned UL resources are based on the SRS.

2. The apparatus of claim 1, wherein to perform the modified LBT procedure, the processing circuitry to:

monitor a channel of the unlicensed spectrum for a single interval window;

in response to the CCA after monitoring the channel of the unlicensed spectrum for the single interval window, encode the SRS for transmission; and in response to lack of the CCA after monitoring the channel of the unlicensed spectrum for the single interval window, abort transmission of the SRS.

3. The apparatus of claim 1, wherein to perform the modified LBT procedure, the processing circuitry to:

select a random backoff count;

for a count of iterations based on the random backoff count:

monitor a channel of the unlicensed spectrum for a contention window time; and

in response to a CCA after monitoring the channel of the unlicensed spectrum for the contention window time, decrement the random backoff count; and

in response to completion of the count of iterations, encode the SRS for transmission.

4. The apparatus of claim 3, wherein for the count of iterations based on the random backoff count, the processing circuitry to, in response to lack of the CCA after monitoring the channel of the unlicensed spectrum for the contention window time, restart the count of iterations.

5. The apparatus of claim 3, wherein for the count of iterations based on the random backoff count, the processing circuitry to, in response to lack of the CCA after monitoring the channel of the unlicensed spectrum for the contention window time:

double the contention window time; and

restart the count of iterations.

6. The apparatus of claim 3, wherein for the count of iterations based on the random backoff count, the processing circuitry to, in response to lack of the CCA after monitoring the channel of the unlicensed spectrum for the contention window time:

reselect a random backoff count; and

restart the count of iterations.

7. The apparatus of claim 3, wherein the contention window time is variable.

8. The apparatus of claim 1, wherein to select the random backoff count includes the processing circuitry to receive the random backoff count from an evolved node B (eNodeB).

9. The apparatus of claims 1-8, further comprising front-end module circuitry to repeat transmission of the SRS across a subset of subcarriers of the unlicensed spectrum based on a repetition factor.

10. The apparatus of claim 9, wherein the repetition factor is greater than two.

11. The apparatus of claim 9, wherein the processing circuitry further to receive subcarrier resource allocation for transmission of the SRS via downlink control information from an evolved node B.

12. The apparatus of claim 1, wherein to encode the SRS for transmission includes the processing circuitry to transmit the SRS at a first symbol period of a designated subframe.

13. An apparatus of evolved Node B (eNodeB), the apparatus comprising: memory; and processing circuitry,

the processing circuitry to:

encode a request for transmission of a sounding reference signal (SRS) in unlicensed spectrum to a user equipment (UE), wherein transmission is facilitated via license-assisted access (LAA), wherein the request for the SRS is included in downlink control information (DCI);

decode the SRS transmission received from the UE in the unlicensed spectrum; and

schedule a frequency band in the unlicensed spectrum for the UE based on the SRS transmission.

14. The apparatus of claim 13, wherein to encode the request for transmission of the SRS in unlicensed spectrum to the UE includes the processing circuitry to provide a narrowband SRS request that includes a subset of subcarriers of the unlicensed spectrum on which to transmit the SRS.

15. The apparatus of claim 13, wherein to encode the request for transmission of the SRS in unlicensed spectrum to the UE includes the processing circuitry to encode a modified listen-before-talk (LBT) procedure type to be used by the UE prior to transmission of the SRS.

16. The apparatus of claim 15, wherein the modified LBT procedure type includes one of no LBT, single interval LBT, or LBT with random backoff.

17. The apparatus of claim 13, wherein to decode the SRS transmission received from the UE in the unlicensed spectrum includes the processing circuitry to receive the SRS in a middle of a downlink burst transmission to the UE.

18. The apparatus of claim 13, wherein to encode the request for transmission of the SRS includes the processing circuitry to:

increase a repetition factor to a new value to provide an increased count of available SRS transmissions slots; and

encode a request for a narrow band SRS transmission to a plurality of user equipments (UEs) that includes the UE, wherein a maximum count of the plurality of UEs is based on the repetition factor.

19. The apparatus of claim 18, wherein the repetition factor is greater than two.

20. At least one machine-readable medium including instructions to transmit a sounding reference signal (SRS) in unlicensed spectrum, which when executed by a machine, cause the machine to:

decode a request for transmission of the SRS in unlicensed spectrum, wherein transmission is facilitated via license-assisted access (LAA);

in response to the request for transmission of the SRS, encode the SRS for transmission in the unlicensed spectrum; and

21. The at least one machine-readable medium of claim 20, further including instructions, which when executed by a machine, cause the machine to perform a modified listen-before-talk (LBT) procedure; wherein the SRS is encoded for transmission further in response to a clear channel assessment (CCA) made as part of the modified LBT procedure.

22. The at least one machine-readable medium of claim 21, wherein to perform the modified LBT procedure includes instructions, which when executed by a machine, cause the machine to:

monitor a channel of the unlicensed spectrum for a single interval window;

23. The at least one machine-readable medium of claim 21, wherein to perform the modified LBT procedure includes instructions, which when executed by a machine, cause the machine to:

select a random backoff count;

for a count of iterations based on the random backoff count:

monitor a channel of the unlicensed spectrum for a contention window time; and

24. The at least one machine-readable medium of claim 23, further including instructions, which when executed by a machine, cause the machine to, for the count of iterations based on the random backoff count, in response to lack of the CCA after monitoring the channel of the unlicensed spectrum for the contention window time, restart the count of iterations.