HK1120347A - Systems and methods for beamforming and rate control in a multi-input multi-output communication systems - Google Patents

Abstract

Methods and apparatuses are disclosed that determine a type of channel information based upon whether a wireless device is scheduled to receive symbols. In addition, a determination may be as to a number of hop periods to determine the type of channel information. Further, a distance between hop regions may be utilized to determine a type of channel information.

Description

System and method for beamforming and rate control in a multiple-input multiple-output communication system

Claiming priority under 35 U.S.C. § 119

The present patent application claims a provisional application No. 60/660,719 entitled "Apparatus to Obtain Pseudo-EigenBeamforming Gains in MIMO Systems" filed on 10.3.2005, and provisional application No. 60/678,610 entitled "SYSTEM AND METHODS FOR GENERATING a beam forming gain in multiple-INPUT multiple-OUTPUT COMMUNICATION SYSTEMS", filed on 6.5.2005, and provisional application No. 60/691,467 entitled "SYSTEMS AND METHODS for Forming multiple-INPUT multiple-OUTPUT COMMUNICATION SYSTEMS", filed on 16.6.2005, AND a provisional application No. 60/691,432 entitled "SYSTEM AND DEMETIIODS FOR BEAM FORMING AND RATE CONTROL IN A MULTI-INPUT ULTI-OUTPUT COMMUNICATION SYSTEM" filed on 16/6/2005, which is assigned to the assignee hereof and is hereby expressly incorporated herein by reference.

I. Reference to co-pending patent applications

This application is related to a co-pending U.S. patent entitled "Systems And Methods For Beamforming In Multi-Input Multi-output communication Systems" filed on even date herewith under attorney docket No. 050507U 2. Application also filed with U.S. patent application No. 60/660,925 filed on 3/10/2005; and united states patent application No. 60/667,705, filed on 1/4/2005, each of which is assigned to the assignee herein and is expressly incorporated herein by reference.

Technical Field

This document relates generally to wireless communications, and more particularly to beamforming for wireless communication systems.

Background

Orthogonal Frequency Division Multiple Access (OFDMA) systems utilize Orthogonal Frequency Division Multiplexing (OFDM). OFDM is a multi-carrier modulation technique that partitions the overall system bandwidth into multiple (N) orthogonal frequency subcarriers. These subcarriers may also be referred to as tones, bins (bins), and frequency channels. Each subcarrier is associated with a respective subcarrier that may be modulated with data. Up to N modulation symbols may be sent on a total of N subcarriers in each OFDM symbol period. These modulation symbols are converted to the time domain using an N-point Inverse Fast Fourier Transform (IFFT) to produce a transformed symbol that contains N time-domain chips or samples.

In a frequency hopping communication system, data is transmitted on different frequency subcarriers during different time intervals, which may be referred to as "hopping periods". These frequency subcarriers may be provided by orthogonal frequency division multiplexing, other multicarrier modulation techniques, or some other concept. With frequency hopping, data transmission hops from subcarrier to subcarrier in a pseudo-random manner. Such hopping provides frequency diversity and allows the data transmission to better withstand adverse path effects such as narrowband interference, jamming, fading, etc.

An OFDMA system may support multiple access terminals simultaneously. For a frequency hopping OFDMA system, data transmissions for a given access terminal may be sent on a "traffic" channel associated with a particular Frequency Hopping (FH) sequence. This FH sequence indicates the particular subcarrier to use for data transmission in each hop period. Multiple data transmissions for multiple access terminals may be sent simultaneously on multiple traffic channels associated with different FH sequences. These FH sequences may be defined to be orthogonal to one another such that only one traffic channel, and thus only one data transmission, uses each subcarrier in each hop period. By using orthogonal FH sequences, multiple data transmissions typically do not interfere with each other while enjoying the benefits of frequency diversity.

A problem that must be dealt with in all communication systems is that the receiver is located in a specific part of the area served by the access point. In such cases where the transmitter has multiple transmit antennas, the signals provided from each antenna need not be combined to provide maximum power at the receiver. In these cases, decoding of the received signal at the receiver may be problematic. One way to deal with these problems is to utilize beamforming.

Beamforming is a spatial processing technique that improves the signal-to-noise ratio of a wireless link having multiple antennas. Generally, beamforming may be used at a transmitter and/or a receiver in a multiple antenna system. Beamforming offers many advantages in improving the signal-to-noise ratio, which improves the decoding of the signal by the receiver.

A problem with beamforming for OFDM transmission systems is obtaining appropriate information about the channel between the transmitter and the receiver to generate beamforming weights in a wireless communication system including OFDM systems. This is problematic due to the complexity required to compute the beamforming weights, as well as the need to provide sufficient information from the receiver to the transmitter.

Disclosure of Invention

The invention provides a method, a device and a system for determining one type of channel information for feedback in a wireless communication system.

In one embodiment, the processor is operable to generate one of the mixed channel information having the best rank, the wideband channel information having the best rank, or the beamformed channel information having the best rank based on whether the apparatus is scheduled.

In another embodiment, a method includes determining whether a wireless communication device is scheduled to receive a symbol. Beamforming channel information is generated if the wireless communication device is scheduled to receive symbols, and wideband channel information is generated if the wireless communication device is not scheduled to receive symbols.

In addition, a decision on the type of channel information to be generated may be notified based on the distance between the current hop region and the previous hop region. Further, the decision on the type of channel information to be generated may be notified based on the number of hopping periods since some type of feedback.

Drawings

The features, nature, and advantages of embodiments of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout and wherein:

fig. 1 illustrates a multiple access wireless communication system according to one embodiment;

fig. 2 illustrates a spectrum allocation scheme for a multiple access wireless communication system according to one embodiment;

fig. 3 illustrates a block diagram of time-frequency allocation for a multiple access wireless communication system in accordance with one embodiment;

fig. 4 illustrates a transmitter and a receiver in a multiple access wireless communication system according to one embodiment;

fig. 5a illustrates a block diagram of a forward link in a multiple access wireless communication system, in accordance with one embodiment;

fig. 5b illustrates a block diagram of a reverse link in a multiple access wireless communication system, in accordance with one embodiment;

fig. 6 illustrates a block diagram of a transmitter system in a multiple access wireless communication system, in accordance with one embodiment;

fig. 7 illustrates a block diagram of a receiver system in a multiple access wireless communication system, in accordance with one embodiment;

fig. 8 illustrates a flow diagram for generating beamforming weights according to one embodiment;

fig. 9 illustrates a flow diagram for generating beamforming weights according to another embodiment;

fig. 10 illustrates a flow diagram for generating beamforming weights according to yet another embodiment;

FIG. 11 illustrates a flow diagram for determining a type of CQI and rank for feedback according to an embodiment; and

fig. 12 illustrates a flow diagram for determining a type of CQI and rank for feedback according to another embodiment.

Detailed Description

Referring to fig. 1, a multiple access wireless communication system is illustrated in accordance with one embodiment. The multiple access wireless communication system 100 includes a plurality of units, such as units 102, 104, and 106. In the embodiment of fig. 1, each unit 102, 104, and 106 may include an access point 150 that includes multiple sectors. The multiple sectors are formed by groups of antennas, each group of antennas being responsible for communication with access terminals in a portion of the cell. In unit 102, antenna groups 112, 114, and 116 each correspond to a different sector. In unit 104, antenna groups 118, 120, and 122 each correspond to a different sector. In unit 106, antenna groups 124, 126, and 128 each correspond to a different sector.

Each cell includes access terminals that communicate with one or more sectors of each access point. For example, access terminals 130 and 132 are in communication with access point 142, access terminals 134 and 136 are in communication with access point 144, and access terminals 138 and 140 are in communication with access point 146.

As can be seen in fig. 1, each access terminal 130, 132, 134, 136, 138, and 140 is located in a different portion of its respective cell than every other access terminal in the same cell. Moreover, each access terminal can be a different distance from the corresponding antenna group with which it is communicating. These two factors, as well as environmental conditions in the cell, result in different channel conditions between each access terminal and its corresponding antenna group with which it is communicating.

As used herein, an access point may be a fixed station used for communicating with the terminals and may also be referred to as, and include some or all the functionality of, a base station, a node B, or some other terminology. An access terminal may also be called and include some or all the functionality of a User Equipment (UE), a wireless communication device, a terminal, a mobile station, or some other terminology.

Referring to fig. 2, a spectrum allocation scheme for a multiple access wireless communication system is illustrated. A plurality of OFDM symbols 200 are allocated over T symbol periods and over S frequency subcarriers. Each OFDM symbol 200 includes one of the T symbol periods and a tone or frequency subcarrier of the S subcarriers.

In an OFDM frequency hopping system, a given access terminal may be assigned one or more symbols 200. In one embodiment of an allocation scheme as shown in fig. 2, one or more hop regions (e.g., hop region 202) of symbols are assigned to a set of access terminals for communication over the reverse link. Within each hop region, the assignment of symbols may be randomized to reduce potential interference and provide frequency diversity to combat adverse path effects.

Each hop region 202 includes symbols 204 assigned to one or more access terminals in communication with a sector of the access point and assigned to the hop region. During each hop period or frame, the position of hop region 202 within the T symbol periods and S subcarriers varies according to the hop sequence. Additionally, assignment of symbols 204 to individual access terminals within hop region 202 may be different for each hop period.

The hop sequence may select the location of hop region 202 for each hop period pseudo-randomly, or according to a predetermined sequence. The hopping sequences for different sectors of the same access point are designed to be orthogonal to each other to avoid "intra-cell" interference between access terminals communicating with the same access point. Further, the hopping sequence for each access point can be pseudo-random with respect to the hopping sequences of nearby access points. This may help randomize "inter-cell" interference between access terminals communicating with different access points.

In the case of reverse link communications, some of the symbols 204 of hop region 202 are assigned to pilot symbols transmitted from the access terminal to the access point. Assigning pilot symbols to symbols 204 preferably should support Spatial Division Multiple Access (SDMA), where signals of different access terminals overlapping on the same hop region may be separated due to multiple receive antennas at a sector or access point, provided there are sufficient spatial signature differences corresponding to the different access terminals.

It should be noted that although fig. 2 depicts hop region 200 having a length of seven symbol periods, the length of hop region 200 may be any desired amount, the size of which may vary between hop periods or between different hop regions in a given hop period.

It should be noted that although the embodiment of fig. 2 is described with respect to utilizing block hopping, the location of the blocks need not be changed between successive hop periods.

Referring to fig. 3, a block diagram of time frequency allocation for a multiple access wireless communication system is illustrated, in accordance with one embodiment. The time-frequency allocation includes a time period 300 that includes broadcast pilot symbols 310 transmitted from the access point to all access terminals with which it is in communication. The time-frequency allocation also includes a time period 302 that includes one or more hop regions 320, each hop region 320 including one or more dedicated pilot symbols 322, the dedicated pilot symbols 322 being transmitted to one or more desired access terminals. The dedicated pilot symbols 322 may comprise the same beamforming weights applied to the data symbols transmitted to the access terminal.

The access terminal may utilize the broadband pilot symbols 310 and the dedicated pilot symbols 322 to generate Channel Quality Information (CQI) for the channel between each transmit antenna that transmits symbols and the receive antenna that receives the symbols for the channel between the access terminal and the access point. In an embodiment, the channel estimate may constitute noise, signal-to-noise ratio, pilot signal power, fading, delay, path loss, shadowing, correlation, or any other measurable characteristic of the wireless communication channel.

In an embodiment, a CQI, which may be an effective signal-to-noise ratio (SNR), may be generated and provided to the access point solely for the broadband pilot symbols 310 (the CQI is referred to as a broadband CQI). The CQI may also be an effective signal-to-noise ratio (SNR) generated and provided to the access point solely for the dedicated pilot symbols 322 (referred to as a dedicated CQI or beamforming CQI). The CQI may include thermal noise and/or an interference covariance matrix per receive antenna or interference level. Interference may be estimated from either the broadband pilots 310 or the dedicated pilot symbols 322. In this way, the access point may know the entire bandwidth available for communication and the CQI for the particular hop region that has been used for transmission to the access terminal. The CQIs from both the broadband pilot symbols 310 and the dedicated pilot symbols 322 independently can provide more accurate rate prediction for the next packet to be transmitted, for larger assignments with random hopping sequences, and for consistent hop region assignments for each user. Regardless of what type of CQI is fed back, in some embodiments, wideband CQI is periodically provided from an access terminal to an access point and can be used for power allocation on one or more forward link channels (e.g., forward link control channels).

Moreover, in those cases where the access terminal is not scheduled for forward link transmission or is irregularly scheduled (i.e., the access terminal is not scheduled for forward link transmission during each hop period), the wideband CQI can be provided to the access point for the next forward link transmission on a reverse link channel (e.g., a reverse link signaling or control channel). This wideband CQI does not include beamforming gain because the wideband pilot symbols 310 are typically not beamformed.

In one embodiment (a TDD system), the access point may use the reverse link transmission from the access terminal to derive beamforming weights based on its channel estimates. The access point may derive a channel estimate based on symbols that include CQI transmitted from the access terminal via a dedicated channel (e.g., a signaling or control channel dedicated to feedback from the access terminal). The channel estimates may be used to generate beamforming weights.

In another embodiment (an FDD system), the access point may derive beamforming weights based on channel estimates determined at the access terminal and provided to the access point via reverse link transmission. If the access terminal also has a reverse link assignment in each frame or hop period (whether in a hop period or frame separate from or the same as the forward link transmission), channel estimate information can be provided to the access point in the scheduled reverse link transmission. The transmitted channel estimates may be used to generate beamforming weights.

In another embodiment (an FDD system), the access point may receive beamforming weights from the access terminals via reverse link transmissions. If the access terminal also has a reverse link assignment in each frame or hop period (whether in a hop period or frame separate from or the same as the forward link transmission), then the beamforming weights may be provided to the access point in the scheduled reverse link transmission.

As used herein, cqi (tdd), channel estimate (FDD), eigenbeam (FDD) feedback, or a combination thereof, may be referred to as channel information, which is utilized by an access point to generate beamforming weights.

Referring to fig. 4, a transmitter and a receiver in a multiple access wireless communication system in accordance with one embodiment are illustrated. At the transmitter system 410, traffic data for a number of data streams is provided from a data source 412 to a Transmit (TX) data processor 444. In an embodiment, each data stream is transmitted via a respective transmit antenna. TX data processor 444 formats, codes, and interleaves the traffic data for each data stream based on a particular coding scheme selected for that data stream to provide coded data. In some embodiments, TX data processor 444 applies beamforming weights to the symbols of the data streams based on the user to which the symbol is being transmitted and the antenna from which the symbol is being transmitted. In some embodiments, beamforming weights may be generated based on channel response information that indicates the condition of the transmission path between the access point and the access terminal. The channel response information may be generated using CQI information or channel estimation values provided by the user. Further, in the case of those scheduled transmissions, TX data processor 444 may select a packet format based on rank information transmitted from the user.

The coded data for each data stream may be multiplexed with pilot data using OFDM techniques. The pilot data is typically a known data pattern that is processed in a known manner and may be used at the receiver system to estimate the channel response. The multiplexed pilot and coded data for each data stream is then modulated (i.e., symbol mapped) based on a particular modulation scheme (e.g., BPSK, QSPK, M-PSK, or M-QAM) selected for that data stream to provide modulation symbols. The data rate, coding, and modulation for each data stream may be determined by instructions performed or provided by processor 430. In some embodiments, the number of parallel spatial streams may vary depending on the rank information transmitted from the user.

The modulation symbols for all data streams are then provided to a TX MIMO processor 446, which TX MIMO processor 446 may further process the modulation symbols (e.g., for OFDM). TX MIMO processor 446 then provides NT symbol streams to NT transmitters (TMTR)422a through 422 t. In certain embodiments, TX MIMO processor 420 applies beamforming weights to the symbols of the data streams from the user channel response information based on the user to which the symbol is being transmitted and the antenna from which the symbol is being transmitted.

Each transmitter 422 receives and processes a respective symbol stream to provide one or more analog signals, and further conditions (e.g., amplifies, filters, and upconverts) the analog signals to provide a modulated signal suitable for transmission over the MIMO channel. NT modulated signals from transmitters 422a through 422t are then transmitted from NT antennas 424a through 424t, respectively.

At receiver system 420, the transmitted modulated signals are received by NR antennas 452a through 452r and the received signal from each antenna 452 is provided to a respective receiver (RCVR)454a through 454 r. Each receiver 454 conditions (e.g., filters, amplifies, and downconverts) a respective received signal, digitizes the conditioned signal to provide samples, and further processes the samples to provide a corresponding "received" symbol stream.

An RX data processor 460 then receives and processes the NR received symbol streams from NR receivers 454a through 454r based on a particular receiver processing technique to provide the rank numbers of the "detected" symbol streams. The processing by RX data processor 460 is described in further detail below. Each detected symbol stream contains symbols that are estimates of the modulation symbols transmitted for the corresponding data stream. RX data processor 460 then demodulates, deinterleaves, and decodes each detected symbol stream to recover the traffic data for the data stream, which is provided to a data receive device (databink) 464 for storage and/or further processing. The processing by RX data processor 460 is complementary to that performed by TX MIMO processor 446 and TX data processor 444 at transmitter system 410.

The channel response estimate generated by RX processor 460 may be used to perform space, space/time processing at the receiver, adjust power levels, change modulation rates or schemes, or other actions. RX processor 460 may further estimate the signal-to-noise-and-interference ratio (SNR) and possibly other channel characteristics for the detected symbol streams and provides these quantities to a processor 470. RX data processor 460 or processor 470 may further derive an estimate of the "effective" SNR for the system. Processor 470 then provides estimated channel information (CSI), which may comprise various types of information regarding the communication link and/or the received data stream. For example, the CSI may comprise only the SNR of operation. In some embodiments, the channel information may include a signal to interference noise ratio (SINR). The CSI is then processed by a TX data processor 478 (which also receives traffic data for a number of data streams from a data source 476), modulated by a modulator 480, conditioned by transmitters 454a through 454r, and transmitted back to transmitter system 410.

At transmitter system 410, the modulated signals from receiver system 450 are received by antennas 424, conditioned by receivers 422, demodulated by a demodulator 490, and processed by a RX data processor 492 to recover the CSI reported by the transmitter system and provide the data to a data receiving device 494 for storage and/or further processing. The reported CSI is then provided to processor 430 and used to (1) determine the data rates and coding and modulation schemes to be used for the data streams and (2) generate various controls for TX data processor 444 and TX MIMO processor 446.

It should be noted that transmitter 410 transmits multiple symbol streams to multiple receivers (e.g., access terminals), while receiver 420 transmits a single data stream to a single structure (e.g., access point), thus illustrating the different receive and transmit chains depicted. However, both may be MIMO transmitters, thus making reception and transmission the same.

At the receiver, the NR received signals may be processed using various processing techniques to detect the NT transmitted symbol streams. These receiver processing techniques can be grouped into two main categories: (i) spatial and space-time receiver processing techniques (which are also referred to as equalization techniques); and (ii) "successive nulling/equalization and interference cancellation" receiver processing techniques (which are also referred to as "successive interference cancellation" or "successive cancellation" receiver processing techniques).

A MIMO channel formed by NT transmit and NR receive antennas can be decomposed into NS independent channels, where N is_s≤min{N_T，N_R}. Each of the NS independent channels may also be referred to as a spatial subchannel (or a transmission channel) of the MIMO channel and corresponds to a dimension.

For a full rank MIMO channel (where N is_S＝N_T≤N_R) In other words, a separate data stream may be transmitted from each of the NT transmit antennas. The transmitted data streams may experience different channel conditions (e.g., different fading and multipath effects), and may achieve different signal-to-noise-and-interference ratios (SNRs) for a given amount of transmit power. Further, in those cases where successive interference cancellation processing is used at the receiver to recover the transmitted data stream, this may be doneDifferent SNRs are achieved for the data streams depending on the particular order in which the data streams are recovered. Thus, different data streams may support different data rates depending on their achieved SNRs. Since channel conditions typically vary over time, the data rate supported by each data stream also varies over time.

MIMO designs may have two modes of operation: single Code Word (SCW) and multiple-code word (MCW). In MCW mode, the transmitter may encode data that is transmitted independently (possibly at different rates) on each spatial layer. The receiver uses a Successive Interference Cancellation (SIC) algorithm, which operates as follows: decoding the first layer; and then after re-encoding the encoded first layer and multiplying it with the "estimated channel", subtract its base value from the received signal, then decode the second layer, and so on. This "onion peeling" approach means that each successively decoded layer experiences an increasing SNR and thus can support higher rates. MCW design with SIC achieves maximum system transmission capability based on channel conditions without error propagation. The drawback of this design stems from the burden of "managing" the rate of each spatial layer: (a) CQI feedback increase (one CQI needs to be provided for each layer); (b) acknowledgment (ACK) or Negative Acknowledgment (NACK) messaging increases (one per layer); (c) hybrid arq (harq) is complicated by the fact that each layer can terminate at a different transmission; (d) performance sensitivity of SIC to channel estimation errors with increased doppler and/or low SNR; and (e) the decoding latency requirement increases because each successive layer cannot be decoded until after the previous layer is decoded.

In the SCW mode design, the transmitter encodes data transmitted on each spatial layer at the "same data rate". The receiver may use a low complexity linear receiver, such as a Minimum Mean Square Solution (MMSE) or Zero Frequency (ZF) receiver, or a non-linear receiver, such as a QRM, for each tone. This allows the receiver to report CQI only for the "best" level and thus results in a reduction in transmission overhead for providing this information.

Referring to fig. 5A, a block diagram of a forward link in a multiple access wireless communication system is illustrated, in accordance with one embodiment. The forward link channel may be modeled as a transmission from multiple transmit antennas 500a through 500t AT an Access Point (AP) to multiple receive antennas 502a through 502r AT an Access Terminal (AT). The forward link channel HFL may be defined as the set of transmission paths from each of the transmit antennas 500 a-500 t to each of the receive antennas 502 a-502 r.

Referring to fig. 5B, a block diagram of a reverse link in a multiple access wireless communication system is illustrated, in accordance with one embodiment. The reverse link channel may be modeled as a transmission from one or more transmit antennas (e.g., antenna 512t) AT an Access Terminal (AT), subscriber station, access terminal, etc., to multiple receive antennas 510 a-510 r AT an Access Point (AP), access point, node b, etc. The reverse link channel HRL may be defined as the set of transmission paths from transmit antenna 512t to each of receive antennas 510 a-510 r.

As can be seen in fig. 5A and 5B, each Access Terminal (AT) may have one or more antennas. In some embodiments, AT an Access Terminal (AT), the number of antennas 512t used for transmission is smaller than the number of antennas 502 a-502 r used for reception. Further, in many embodiments, the number of transmit antennas 500 a-500 t at each Access Point (AP) is greater than either or both of the number of transmit or receive antennas at the access terminal.

In time division duplex communication (time division duplex communication), if the number of antennas used for transmission at the access terminal is less than the number of antennas used for reception at the access terminal, there is no full channel reciprocity. Thus, the forward link channels for all receive antennas at the access terminal are difficult to obtain.

In frequency division duplex communication, feeding back channel state information for all eigenbeams of a forward link channel matrix may be ineffective or nearly impossible due to limited reverse link resources. Thus, the forward link channels for all receive antennas at the access terminal are difficult to obtain.

In an embodiment, channel feedback is provided from an access terminal to an access point for a subset of possible transmission paths between transmit antennas at the access point and receive antennas at the access terminal.

In an embodiment, the feedback may consist of a CQI generated by the access point based on one or more symbols transmitted from the access terminal to the access point, e.g., via a pilot or control channel. In these embodiments, a channel estimate for a number of transmission paths equal to the number of transmit antennas utilized at the access terminal for each receive antenna of the access point may be derived from the CQI by considering the CQI as a pilot. This allows beamforming weights to be re-calculated on a regular basis and thus more accurately respond to the condition of the channel between the access terminal and the access point. This approach reduces the complexity of the processing required at the access terminal because there is no processing associated with generating beamforming weights at the access terminal. The channel estimate obtained from the CQI may be used at the access point to generate a beamforming matrix, b (k) ═ h^FL(k)*b₂..b_M]Wherein b is₂，b₃，...，b_MIs a random vector, and h^FL(k) Is a channel derived by using CQI as a pilot. The information for hfl (k) may be obtained by determining hrl (k) at the Access Point (AP). Note that hrl (k) is a channel estimate of the responsive pilot symbols transmitted on the reverse link from the transmit antennas of the Access Terminal (AT). It should be noted that the hRL is only provided for the number of transmit antennas at the access terminal (depicted as 1 in fig. 5B), which is less than the number of receive antennas at the access terminal (depicted as r in fig. 5A). The channel matrix hfl (k) is obtained by calibrating the hrl (k) with a matrix Λ, which is a function of the difference between the reverse link channel and the calculated forward link information received from the access terminal. In one embodiment, the matrix Λ may be defined as shown below, where λ₁Is the calibration error for each channel and is,

to calculate the calibration error, the forward direction may be utilizedBoth link and reverse link channel information. In some embodiments, the coefficient λ may be determined at regular intervals based on overall channel conditions₁And coefficient λ₁And is not specific to any particular access terminal communicating with the access point. In other embodiments, the coefficient λ may be determined by utilizing an average from each of the access terminals in communication with the access point₁。

In another embodiment, the feedback may consist of eigenbeams calculated at the access terminal based on pilot symbols transmitted from the access point. The eigenbeams may be averaged over several forward link frames or correlated to a single frame. Furthermore, in some embodiments, the eigenbeams may be averaged over multiple tones in the frequency domain. In other embodiments, only the dominant eigenbeams of the forward link channel matrix are provided. In other embodiments, the dominant eigenbeams may be averaged for two or more frames in the time domain, or may be averaged over multiple tones in the frequency domain. Doing so may reduce both computational complexity at the access terminal and transmission resources required to provide an eigenbeam from the access terminal to the access point. When 2 quantized eigenbeams are provided, an exemplary beam construction matrix generated at the access point is given by: b (k) ═ q₁(k)q₂(k)b₃...b_M]Wherein q is_i(k) Is the quantized eigenbeam provided, and b3... bM is a dummy vector or otherwise generated by the access terminal.

In another embodiment, the feedback may consist of quantized channel estimates computed at the access terminal based on pilot symbols transmitted from the access point. The channel estimates may be averaged over several forward link frames or correlated with a single frame. Further, in some embodiments, the channel estimates may be averaged over multiple tones in the frequency domain. An exemplary beamforming matrix generated at the access point when 2 rows of the FL-MIMO channel matrix are provided is given by: b (k) ═ b (2 [, ]<H^FL>₁<H^FL>₂ b₃...b_M]Wherein<H^FL>_iIs FL-MRow i of the IMO channel matrix.

In another embodiment, the feedback may include secondary statistics (i.e., transmit correlation matrices) of the channel calculated at the access terminal based on pilot symbols transmitted from the access point. The secondary statistics may be averaged over several forward link frames or correlated to a single frame. In some embodiments, the channel statistics may be averaged over multiple tones in the frequency domain. In this case, the eigenbeams may be derived from a transmit correlation matrix at the AP, and a beam construction matrix may be created as: b (k) ═ q₁(k)q₂(k)q₃(k) ...q_M(k)]Wherein q is_i(k) Is an eigenbeam.

In another embodiment, the feedback may include eigenbeams of secondary statistics (i.e., transmit correlation matrices) of the channel calculated at the access terminal based on pilot symbols transmitted from the access point. The eigenbeams may be averaged over several forward link frames or correlated to a single frame. Furthermore, in some embodiments, the eigenbeams may be averaged over multiple tones in the frequency domain. In other embodiments, only the dominant eigenbeams of the transmit correlation matrix are provided. The dominant eigenbeams may be averaged over several forward link frames or correlated to a single frame. Furthermore, in some embodiments, the dominant eigenbeams may be averaged over multiple tones in the frequency domain. An exemplary beam construction matrix when feeding back 2 quantized eigenbeams is given by: b (k) ═ q₁(k)q₂(k)b₃ ...b_M]Wherein q is_i(k) Is the quantized eigenbeams per hop of the transmit correlation matrix.

In further embodiments, the beam construction matrix may be generated by a combination of channel estimates obtained from the CQI and dominant eigenbeam feedback. An exemplary beam construction matrix is given by:

equation 5

Where x1 is the dominant eigenbeam of particular hFL, and h_FL ^*Based on the CQI.

In other embodiments, the feedback may consist of the CQI and the estimated eigenbeams, the channel estimate, the transmit correlation matrix, the eigenbeams of the transmit correlation matrix, or any combination thereof.

The beam construction matrix may be generated at the access point using a channel estimate obtained from the CQI, an estimated eigenbeam, a channel estimate, a transmit correlation matrix, an eigenbeam of the transmit correlation matrix, or any combination thereof.

To form the beamforming vector for each transmission, a QR decomposition of the beamforming matrix B is performed to form pseudo-eigenvectors (pseudo-eigenvectors) that each correspond to a set of transmission symbols transmitted from the MT antennas to a particular access terminal.

V＝QR(B)

V＝［v₁ v₂...v_M]Are pseudo eigenvectors. Equation 6

The individual scalars of the beamforming vectors represent beamforming weights applied to symbols transmitted from the MT antennas to each access terminal. These vectors are then formed by the following equation:

equation 7

Where M is the number of layers used for transmission.

To determine how many eigenbeams should be used (rank prediction) and what transmission mode should be used to obtain the maximum eigenbeamforming gain, several approaches may be utilized. If the access terminal is not scheduled, an estimate, such as a 7-bit channel estimate that may include rank information, may be calculated based on the wideband pilot and reported along with the CQI. The control or signaling channel information transmitted from the access terminal acts as a broadband pilot for the reverse link after decoding. Using this channel, beamforming weights can be calculated as shown above. The computed CQI also provides information for the rate prediction algorithm at the transmitter.

Alternatively, if the access terminal is scheduled to receive data on the forward link, a CQI (e.g., including the CQI for the best rank and the CQI for that rank) can be calculated based on beamformed pilot symbols (e.g., pilot symbols 322 from fig. 3) and fed back via a reverse link control or signaling channel. In these cases, the channel estimate contains the eigen-beamforming gain and provides a more accurate rate and level prediction for the next packet. Also, in some embodiments, the beamformed CQI may be periodically corrupted with wideband CQI, and thus in such embodiments, the beamformed CQI may not always be available.

If the access terminal is scheduled to receive data on the forward and reverse links, a CQI (e.g., CQI) can be based on the beamformed pilot symbols and can also be reported in-band (i.e., during reverse link transmissions to the access point).

In another embodiment, the access terminal may calculate a broadband pilot based CQI and a hopping based pilot channel CQI for all tiers. Thereafter, the access terminal may compute beamforming gains provided due to beamforming at the access point. The beamforming gain may be calculated by the difference between the wideband pilot and the CQI of the hop-based pilot. After the beamforming gain is calculated, it can be factored into the CQI calculation for the broadband pilot to form a more accurate channel estimate for all levels of the broadband pilot. Finally, a CQI comprising the best rank and a channel estimate for that rank is obtained from this effective broadband pilot channel estimate and fed back to the access point via a control or signaling channel.

Referring to fig. 6, a block diagram of a transmitter system in a multiple access wireless communication system is illustrated, in accordance with one embodiment. The transmitter 600 generates an information stream based on the channel information using a rate prediction block 602 that controls a single-input single-output (SISO) encoder 604.

Depending on the Packet Format (PF)624 assigned by the rate prediction block 602, the bits are turbo encoded by an encoder block 606 and mapped to modulation symbols by a mapping block 608. The encoded symbols are then demultiplexed by demultiplexer 610 to M_TA layer 612, said M_TThe individual layers 612 are provided to a beamforming module 614.

The beamforming module 614 generates beamforming weights for changing M depending on the access terminal to which the beamforming weights are to be transmitted_TThe transmission power of each of the symbols of layer 612. Dependent on control transmitted by the access terminal to the access pointChannel information is modulated or signaled to generate eigenbeam weights. The beamforming weights may be generated according to any of the embodiments described above with reference to fig. 5A and 5B.

M after beamforming_TLayers 612 are provided to OFDM modulators 618a through 618t, which interleave the output symbol streams with pilot symbols. OFDM processing for each transmit antenna then proceeds in the same manner from 620a to 620t, after which the signals are transmitted via a MIMO scheme.

In SISO encoder 604, turbo encoder 606 encodes the data stream, and in one embodiment uses an 1/5 encoding rate. It should be noted that other types of encoders and encoding rates may be utilized. The symbol encoder 608 maps the encoded data into constellation symbols (constellation symbols) for transmission. In one embodiment, the clusters may be quadrature-amplitude clusters. Although SISO encoders are described herein, other encoder types including MIMO encoders may be utilized.

The rate prediction block 602 processes CQI information (including rank information) that is received at the access point for each access terminal. Rank information may be provided based on wideband pilot symbols, hop-based pilot symbols, or both. The level information is used to determine the number of spatial layers to be transmitted by the rate prediction block 602. In an embodiment, the rate prediction algorithm may use a 5-bit CQI feedback 622 approximately every 5 milliseconds. Several techniques are used to determine the packet format (e.g., modulation rate). Exemplary techniques are described and disclosed in co-pending U.S. patent application No. 11/021,791 entitled "Performance Based Rank Prediction for MIMO Design" and U.S. patent application No. 11/022,347 entitled "Capacity Based Rank Prediction for MIMO Design," which are incorporated by reference herein as if set forth in their entirety.

Referring to fig. 7, a block diagram of a receiver system in a multiple access wireless communication system is illustrated, in accordance with one embodiment. In fig. 7, each antenna 702 a-702 t receives one or more symbols intended for receiver 700. Antennas 702a through 702t are each coupled to OFDM demodulators 704a through 704t, and OFDM demodulators 704a through 704t are each coupled to a skip buffer 706. OFDM demodulators 704a through 704t each demodulate OFDM received symbols into received symbol streams. Hop buffer 706 stores the received symbols for the hop region in which they are transmitted.

The output of the skip buffer 706 is provided to an encoder 708, which encoder 708 may be a decoder that processes each carrier frequency of the OFDM band independently. Both hop buffer 706 and decoder 708 are coupled to a hop-based channel estimator 710. hop-based channel estimator 710 uses the estimate of the forward link channel and the eigenbeam weights to demodulate the information stream. The demodulated information stream provided by demodulator 712 is then provided to a log-likelihood-ratio (LLR) block 714 and a decoder 716, which may be a turbo decoder or other decoder to match an encoder used at the access point, which provides a decoded data stream for processing.

Referring to fig. 8, a flow diagram of generating beamforming weights is illustrated, in accordance with one embodiment. The CQI information is read from a memory or buffer, block 800. In addition, the CQI information may be replaced with eigenbeam feedback provided from the access terminal. The information may be stored in a buffer or may be processed in real time. The channel matrix for the forward link is constructed using the CQI information as a pilot, block 802. The beam construction matrix may be constructed as discussed with reference to fig. 5A and 5B. The beamforming matrix is then decomposed, block 804. The decomposition may be a QR decomposition. Eigenvectors representing the beamforming weights may then be generated for the symbols of the next hop region to be transmitted to the access terminal, block 806.

Referring to fig. 9, a flow diagram of generating beamforming weights in accordance with another embodiment is illustrated. Channel estimate information provided from the access terminal is read from a memory or buffer, block 900. The channel estimate information may be stored in a buffer or may be processed in real time. A beam construction matrix for the forward link is constructed using the channel estimate information, block 902. The beam construction matrix may be constructed as discussed with reference to fig. 5A and 5B. The beamforming matrix is then decomposed, block 904. The decomposition may be a QR decomposition. Eigenvectors representing beamforming weights may then be generated for symbols of the next hop region to be transmitted to the access terminal, block 906.

Referring to fig. 10, a flow diagram of generating beamforming weights is illustrated, according to yet another embodiment. The eigenbeam information provided from the access terminal is read from a memory or buffer, block 1000. In addition, channel information is also read, block 1002. The channel information may include CQI, channel estimates, SINR, SNR, and/or secondary channel statistics (wherever originally generated). The eigenbeam information and the channel information may be stored in a buffer or may be processed in real time. The beam construction matrix for the forward link is constructed using the eigenbeam information and the channel information, block 1004. The beam construction matrix may be constructed as discussed with reference to fig. 5A and 5B. The beamforming matrix is then decomposed, block 1006. The decomposition may be a QR decomposition. Eigenvectors representing the beamforming weights may then be generated for the symbols of the next hop region to be transmitted to the access terminal, block 1008.

Referring to fig. 11, a flow diagram of determining a type of CQI and rank for feedback in accordance with one embodiment is illustrated. A determination is made as to whether the access terminal is scheduled to receive a transmission, block 1100. In an embodiment, this may be based on whether the access terminal is scheduled to receive symbols in the next hop period. In other embodiments, this may be based on whether the access terminal is scheduled to receive symbols in one or more of the following N hop periods, where N is based on the system parameters.

If the access terminal is not scheduled, channel information (e.g., CQI) and best rank are determined based on the broadband pilot symbols, block 1102. If the access terminal is scheduled, it is additionally determined whether the number of hop periods is greater than N hop periods because beamformed channel information has been provided, block 1104.

If the number is less than N, then either wideband channel information is provided with the best level based on the channel information (block 1106), or hybrid channel information is provided with the best level based on the channel information (block 1108). Whether wideband channel information or mixed channel information is provided may be based on system design. Alternatively, the wideband channel information and the mixed channel information may be provided in the form of alternating signals or based on a predetermined pattern.

If the number is greater than N, then beamformed channel information is provided along with a best level based on the channel information (block 1110), or hybrid channel information is provided along with a best level based on the channel information (block 1108). Whether beamformed channel information or hybrid channel information is provided may be based on system design. Alternatively, the beamformed channel information and the mixed channel information may be provided in the form of alternating signals or based on a predetermined pattern.

Referring to fig. 12, a flow diagram of determining a type of CQI and rank for feedback in accordance with another embodiment is illustrated. A determination is made whether the access terminal is scheduled to receive a transmission, block 1200. In an embodiment, this may be based on whether the access terminal is scheduled to receive symbols in the next hop period. In other embodiments, this may be based on whether the access terminal is scheduled to receive symbols in one or more of the following N hop periods, where N is based on the system parameters.

If the access terminal is not scheduled, then channel information (e.g., CQI) and best rank are determined based on the broadband pilot symbols, block 1202. If the access terminal is scheduled, it is additionally determined whether the distance between the locations of the current hop region and the previous hop region is greater than a threshold, block 1204. The previous hop region may be a hop region for an immediately preceding hop period or for a hop period earlier than the current hop period. The threshold may be a function of a system parameter.

If the distance is greater than a threshold, wideband channel information is provided along with an optimal level based on the channel information (block 1206), or hybrid channel information is provided along with an optimal level based on the channel information (block 1208). Whether wideband channel information or mixed channel information is provided may be based on system design. Alternatively, the wideband channel information and the mixed channel information may be provided in the form of alternating signals or based on a predetermined pattern.

If the distance is less than a threshold, then beamformed channel information is provided along with a best level based on the channel information (block 1210), or hybrid channel information is provided along with a best level based on the channel information (block 1208). Whether beamformed channel information or hybrid channel information is provided may be based on system design. Alternatively, the beamformed channel information and the mixed channel information may be provided in the form of alternating signals or based on a predetermined pattern.

It should be noted that block 1104 or block 1204 may be skipped and, if the access terminal is scheduled, beamformed channel information or mixed channel information may be provided according to a system design or a predetermined pattern.

The above-described processes may be performed by TX processor 444 or 478, TX MIMO processor 446, RX processor 460 or 492, processor 430 or 470, memory 432 or 472, and combinations thereof. The additional processes, operations, and features described with reference to fig. 5A, 5B, and 6-10 may be executed on any processor, controller, or other processing device and may be stored as source code, object code, or otherwise as computer-readable instructions in a computer-readable medium.

The techniques described herein may be implemented by various means. For example, these techniques may be implemented in hardware, software, or a combination thereof. For a hardware implementation, the processing units within an access point or access terminal may be implemented within one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof.

For a software implementation, the techniques described herein may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in memory units and executed by processors. The memory unit may be implemented within the processor or external to the processor, in which case it can be communicatively coupled to the processor via various means as is known in the art.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the features, functions, operations, and embodiments disclosed herein. Various modifications to these embodiments may be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope thereof. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (32)

1. An apparatus, comprising:

a memory; and

a processor coupled with the memory, the processor operable to generate one of mixed channel information having a best rank, wideband channel information having a best rank, or beamformed channel information having a best rank based on whether the apparatus is scheduled.

2. The apparatus of claim 1, wherein the processor is further operable to determine whether the apparatus is scheduled when the apparatus has received an instruction that it will receive a symbol in a next hop period.

3. The apparatus of claim 1, wherein the processor is further operable to determine whether the apparatus is scheduled when the apparatus has received an instruction that it will receive symbols in at least one of N subsequent hop periods.

4. The apparatus of claim 1, wherein the processor is further operable to generate one of the mixed channel information with a best rank, wideband channel information with a best rank, or beamformed channel information with a best rank based on whether the apparatus is scheduled and a number of hop periods.

5. The apparatus of claim 1, wherein the processor is further operable to generate one of the mixed channel information having a best rank, wideband channel information having a best rank, or beamformed channel information having a best rank based on whether the apparatus is scheduled and a distance between a previous hop region and a current hop region.

6. The apparatus of claim 1, wherein the previous hop region is an immediately preceding hop region.

7. The apparatus of claim 1, wherein the processor is further operable to cause signals to be transmitted utilizing an orthogonal frequency division multiplexing (0FDM) scheme.

8. The apparatus of claim 1, wherein the processor is further operable to generate the mixed channel information by modifying the wideband channel information based on a difference between the wideband channel information and the beamformed channel information.

9. The apparatus of claim 1, wherein each of the mixed channel information with best rank, wideband channel information with best rank, and beamformed channel information with best rank consists of 7 bits.

10. The apparatus of claim 1, wherein the best rank consists of 2 bits.

11. The apparatus of claim 1, wherein the processor is further operable to quantize mixed channel information having a best level, wideband channel information having a best level, and beamformed channel information having a best level.

12. The apparatus of claim 1, wherein the processor is further operable to generate the mixed channel information and beamformed channel information based only on dominant eigenbeams.

13. The apparatus of claim 1, wherein the channel information comprises a CQI that constitutes an estimate of a signal-to-noise ratio of the received symbols.

14. The apparatus of claim 13, wherein the CQI comprises thermal noise, an interference covariance matrix per receive antenna, or an interference variance.

15. The apparatus of claim 14, wherein the processor is further configured to estimate the interference covariance matrix or interference variance per receive antenna in accordance with a broadband pilot or dedicated pilot or a mixing scheme that may include interference estimated in accordance with broadband and dedicated pilots.

16. A method, comprising:

determining whether a wireless communication device is scheduled to receive a symbol;

generating beamforming channel information if the wireless communication device is scheduled to receive symbols; and

wideband channel information is generated if the wireless communication device is not scheduled to receive symbols.

17. The method of claim 14, wherein determining whether the wireless communication device is scheduled comprises determining whether the wireless communication device has received an instruction that it will receive symbols in a next hop period.

18. The method of claim 14, wherein determining whether the wireless communication device is scheduled comprises determining whether the wireless communication device has received an instruction that it will receive symbols in at least one of N subsequent hop periods.

19. The method of claim 14, further comprising

Determining a number of hop periods;

generating one of hybrid channel information or beamforming channel information if the number of hop periods is greater than a predetermined number; and

if the number of hop periods is less than the predetermined number, wideband channel information or mixed channel information is generated.

20. The method of claim 14, further comprising

Determining whether a distance between a previous jump zone and a current jump zone exceeds a threshold;

generating one of the hybrid channel information or beamforming channel information if the distance is greater than the threshold; and

generating the wideband channel information or mixed channel information if the distance is less than the threshold.

21. The method of claim 18, wherein the previous hop region is an immediately preceding hop region.

22. The method of claim 14, wherein each of the wideband channel and beamformed channel information consists of 5 bits.

23. The method of claim 14, further comprising quantizing the generated wideband channel information or beamformed channel information.

24. The method of claim 14, wherein the beamformed channel information is generated based only on dominant eigenbeams.

25. The method of claim 14, wherein the channel information comprises CQI.

26. An apparatus, comprising:

means for determining whether a wireless communication device is scheduled to receive symbols; and

means for generating one of mixed channel information having a best rank, wideband channel information having a best rank, or beamformed channel information having a best rank based on whether the apparatus is scheduled.

27. The apparatus of claim 14, wherein the means for determining whether the wireless communication device is scheduled comprises means for determining whether the wireless communication device has received an instruction that it will receive a symbol in a next hop period.

28. The apparatus of claim 24, wherein the means for determining whether the wireless communication device is scheduled comprises means for determining whether the wireless communication device has received an instruction that it will receive symbols in at least one of N subsequent hop periods.

29. The apparatus of claim 24, further comprising means for determining a number of hop periods, and wherein the generating means comprises means for generating one of the mixed channel information with a best rank, the wideband channel information with a best rank, or the beamformed channel information with a best rank based on whether the apparatus is scheduled and the number of hop periods.

30. The apparatus of claim 24, further comprising whether a distance between a previous hop region and a current hop region exceeds a threshold, and wherein the means for generating comprises means for generating one of the mixed channel information with a best level, the wideband channel information with a best level, or the beamformed channel information with a best level based on whether the apparatus is scheduled and whether the distance between the previous hop region and the current hop region exceeds the threshold.

31. The apparatus of claim 28, wherein the previous hop region is an immediately preceding hop region.

32. The apparatus of claim 24, wherein the channel information comprises CQI.