Systems and methods for beamforming feedback in multi antenna communication systems

The present application claims priority from Provisional Application Ser. No. 60/665,120, filed Mar. 24, 2005, entitled “PSEUDO-EIGENBEAMFORMING IN FDD SYSTEMS”, Provisional Application Ser. No. 60/691,808, filed Jun. 16, 2005, entitled “SYSTEMS AND METHODS FOR EIGEN-BEAMFORMING IN MULTI ANTENNA COMMUNICATIONS SYSTEMS”, and Provisional Application Ser. No. 60/710,402, filed Aug. 22, 2005, entitled “SYSTEMS AND METHODS FOR BEAM FORMING FEEDBACK IN MULTI ANTENNA COMMUNICATION SYSTEMS,” which are assigned to the assignee hereof, and expressly incorporated by reference herein in their entirety.

The present Application is related to the following co-pending U.S. Patent Application: “Systems And Methods For Generating Beamforming Gains In Multi-Input Multi-Output Communication Systems,” application Ser. No. 11/186,152 filed on Jul. 20, 2005; U.S. patent application Ser. No. 11/186,697, titled “Systems And Methods For Generating Beamforming Gains In Multi-Input Multi-Output Communication Systems,” filed on Jul. 20, 2005, Application Ser. No. 60/660,925 filed Mar. 10, 2005; and U.S. Patent Application: “Systems And Methods For Generating Beamforming Gains In Multi-Input Multi-Output Communication Systems,” filed on even date herewith, Application Ser. No. 60/667,705 filed Apr. 1, 2005, each of which are assigned to the assignee hereof, and expressly incorporated by reference herein.

I. Field

The present document relates generally to wireless communication and amongst other things to eigen-beam forming for wireless communication systems.

II. Background

An orthogonal frequency division multiple access (OFDMA) system utilizes 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 called tones, bins, and frequency channels. Each subcarrier is associated with a respective sub carrier that may be modulated with data. Up to N modulation symbols may be sent on the N total subcarriers in each OFDM symbol period. These modulation symbols are converted to the time-domain with an N-point inverse fast Fourier transform (IFFT) to generate 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 “hop periods.” These frequency subcarriers may be provided by orthogonal frequency division multiplexing, other multi-carrier modulation techniques, or some other constructs. With frequency hopping, the data transmission hops from subcarrier to subcarrier in a pseudo-random manner. This hopping provides frequency diversity and allows the data transmission to better withstand deleterious path effects such as narrow-band interference, jamming, fading, and so on.

A problem in most communication systems is that the receiver is located in a specific portion of an area served by the access point. In such cases, where a 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, there may be problems with decoding of the signals received at the receiver. One way to deal with these problems is by utilizing beamforming.

Beamforming is a spatial processing technique that improves the signal-to-noise ratio of a wireless link with multiple antennas. Typically, beamforming may be used at either the transmitter or the receiver in a multiple antenna system. Beamforming provides many advantages in improving signal-to-noise ratios which improves decoding of the signals by the receiver.

Certain types of OFDMA systems are frequency division duplexed (FDD) OFDMA systems. In these FDD OFDMA systems, the transmission from the access point to the access terminal and from the access terminal to the access point occupy different distinct frequency bands. In FDD OFDMA systems feedback to perform beamforming generally requires knowledge of the channel at the transmitter, e.g. access point, which is not available without substantial feedback. This feedback, generally in the form of the actual beamforming weights or vectors, requires a large amount of resources on control or signaling channels. This reduces data rates and increases the overhead required.

Therefore, it is desired that systems provide feedback for more accurate beamforming while minimizing the resources needed to provide the feedback from the receiver to the transmitter.

In some embodiments, available reverse link transmission resources allocated for transmission of beamforming information are determined based upon the determination of the available reverse link transmission resources. In some embodiments, this may be performed by a processor or other means. Further, in some embodiments this information is transmitted over the air as an instruction.

In certain embodiments, a determination whether to transmit eigenbeam information from the at least one antenna is based upon channel information. In some embodiments, the channel information may be channel statistics or second order channel statistics. In other embodiments, the channel information may be instantaneous channel information.

It is understood that other aspects of the present disclosure will become readily apparent to those skilled in the art from the following detailed description, wherein is shown and described only exemplary embodiments of the disclosure, simply by way of illustration. As will be realized, the embodiments disclosed are capable of other and different embodiments and aspects, and its several details are capable of modifications in various respects, all without departing from the scope of the disclosure.

The features, nature, and advantages of the present embodiments may 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 an embodiment;

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

FIG. 3 illustrates a conceptual block diagram of eigenbeams experienced by a receiver in a wireless communication system according to an embodiment;

FIG. 4 illustrates a transmitter and receiver in a multiple access wireless communication system an embodiment;

FIG. 5 illustrates a block diagram of a transmitter system in a multiple access wireless communication system according to an embodiment;

FIG. 6 illustrates a block diagram of a receiver system in a multiple access wireless communication system according to an embodiment;

FIG. 7 illustrates a flow chart of determining resources to be allocated for providing eigenbeam feedback according to an embodiment;

FIG. 8 illustrates a flow chart of determining whether to provide eigenbeam feedback according to another embodiment;

FIG. 9 illustrates a flow chart of generating eigenbeam vectors according to a further embodiment; and

FIG. 10 illustrates a flow chart of generating eigenbeam feedback according an embodiment.

Referring to FIG. 1 , a multiple access wireless communication system according to one embodiment is illustrated. A multiple access wireless communication system 100 includes multiple cells, e.g. cells 102 , 104 , and 106 . In the embodiment of FIG. 1 , each cell 102 , 104 , and 106 may include an access point 150 that includes multiple sectors. The multiple sectors may be formed by groups of antennas each responsible for communication with access terminals in a portion of the cell. In cell 102 , antenna groups 112 , 114 , and 116 each correspond to a different sector. In cell 104 , antenna groups 118 , 120 , and 122 each correspond to a different sector. In cell 106 , antenna groups 124 , 126 , and 128 each correspond to a different sector.

Each cell includes several access terminals which may be in communication with one or more sectors of each access point. For example, access terminals 130 and 132 are in communication base station 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 .

It can be seen from FIG. 1 that each access terminal 130 , 132 , 134 , 136 , 138 , and 140 is located in a different portion of its respective cell than each other access terminal in the same cell. Further, each access terminal may be a different distance from the corresponding antenna groups with which it is communicating. Both of these factors provide situations, also due to environmental and other conditions in the cell, to cause different channel conditions to be present 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 referred to as, and include some or all the functionality of, a user equipment (UE), a wireless communication device, 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 is allocated over T symbol periods and S frequency subcarriers. Each OFDM symbol 200 comprises one symbol period of the T symbol periods and a tone or frequency subcarrier of the S subcarriers.

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

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

The hop sequence may pseudo-randomly, randomly, or according to a predetermined sequence, select the location of the hop region 202 for each hop period. The hop sequences for different sectors of the same access point may be designed to be orthogonal to one another to avoid “intra-cell” interference among the access terminal communicating with the same access point. Further, hop sequences for each access point may be pseudo-random with respect to the hop sequences for nearby access points. This may help randomize “inter-cell” interference among the access terminals in communication with different access points.

In the case of a reverse link communication in an FDD communication system, the frequency subbands 1 to S do not overlap with any of the subbands of 1 to S of the forward link. In the reverse link, some of the symbols 204 of a hop region 202 may be assigned to pilot symbols that may be transmitted from the access terminals to the access point. The assignment of pilot symbols to the symbols 204 should, in an embodiment, support space division multiple access (SDMA), where signals of different access terminals overlapping on the same hop region can be separated due to multiple receive antennas at a sector or access point, provided enough difference of spatial signatures corresponding to different access terminals.

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

Also, it should be noted that while the embodiment of FIG. 2 is described with respect to utilizing block hopping, the location of the block need not be altered between consecutive hop periods.

Referring to FIG. 3 , a conceptual block diagram of eigenbeams experienced at a wireless communication system according to one embodiment is illustrated. A transmitter 300 , which may be an access point, transmits multiple symbols during a given hop period intended for receiver 304 , which may be an access terminal. Signals transmitted from transmitter 300 are transmitted from antennas 302 a , 302 b , 302 c , . . . , 302 t and received by receiver 304 at antennas 306 a , 306 b , 306 c , . . . , 306 r . This forms a MIMO channel between transmitter 300 and receiver 304 . In transmitting symbols from transmitter 300 to receiver 304 , transmitter 300 eigenbeamforms the symbols. Eigenbeamforming is a technique that combines beamforming, diversity and spatial multiplexing gains, using eigenvectors to multiply, phase shift, and/or amplitude shifts of symbols for transmission depending on the antenna from which they are to be transmitted.

In one embodiment, a transmitter 300 transmits pilot symbols from antennas 302 a , 302 b , 302 c , . . . , 302 t which are used by the receiver 304 to estimate the downlink channel and calculate its correlation matrix. Then, the receiver 304 performs eigenvalue decomposition of the correlation matrix and provides information regarding the eigenvectors to the transmitter 300 . In some embodiments, the receiver 304 determines which of the eigenvector beam patterns would yield the highest signal-to-noise ratio (SNR) or other desired signal characteristics and transmits this information to the base station which may use this eigenvector information for beam shaping for data signal transmission to this mobile station on later transmissions.

As depicted in FIG. 3 , the eigenbeams may have several (local) maxima 308 a , 308 b , and 308 c pointing in different directions. Other eigenbeams may have portions 310 a , and 310 b that point in other directions but have a lower magnitude, as received at receiver 304 , than eigenbeams having maxima 308 a , 308 b , and 308 c . Further, the radiation pattern and therefore those eigenbeams having the greatest maxima of can vary over time as the channel conditions, the location of the receiver, or other factors change.

In order to provide sufficient information for performing eigenbeamforming at transmitter 300 , receiver 304 provides feedback information regarding the eigenvectors to transmitter 300 . In an embodiment, feedback is provided based upon the channel conditions. For example, in an embodiment, if channel conditions are substantially unchanging feedback may be provided. In other embodiments, if channel conditions have recently changed then feedback may be provided. In additional, embodiments, if channel conditions are constantly changing, no feedback or minimum feedback may be provided. In further embodiments, feedback may be provided if there is a recent change in the channel conditions or channel conditions are substantially unchanging. In some embodiments, changes in channel conditions may be determined by changes in channel statistics, instantaneous channel information or signal-to-noise ratios.

In one embodiment, the feedback may comprise eigenvectors calculated at the receiver 304 for the dominant eigenbeams experienced by the receiver 304 . In some embodiments, the information regarding the eigenvectors for the dominant eigenbeams is quantized according to a codebook and then the quantized bits are transmitted to the transmitter 302 that includes a codebook for reading the quantized bits.

In an embodiment, the quantized bits are based on the minimum mean square error between the codebook and the dominant eigenbeams, or the dominant beams and the other eigenbeams.

The feedback provided by the access terminal is utilized to form a preliminary beamforming matrix comprising a plurality of eigenvectors that have been feedback from the receiver to the transmitter. Due to limited reverse link resources, this preliminary beamforming matrix may not comprise of all the eigenvectors necessary for transmission.

In order to form the set of eigenbeamforming vectors that provide the best available transmission characteristics, a QR decomposition of the beamforming matrix is performed to form the complete set of eigenvectors, as follows:

B=[v 1 v 2 . . . v k ] are the K-eigen vectors that have been fedback B is the “preliminary” beamforming matrix. V is the “final” beamforming matrix consisting of the complete set of eigenvectors.

V=[v 1 v 2 . . . v k v k+1 . . . v M ]

v k+1 . . . v M are the pseudo-eigenvectors that have been generated from the QR decomposition

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

F M = 1 M ⁡ [ v 1 v 2 ⋯ v M ] Eq . ⁢ 6

where M is the number of layers utilized for transmission. In order to decide how many eigenbeams should be used (rank prediction), and what transmission mode should be used to obtain maximum eigenbeamforming gains, several approaches may be utilized. If the access terminal is not scheduled, the eigenbeam feedback, e.g. a 7-bit or other sized feedback may include rank information, may be computed based on from the broadband pilots and reported along with the eigenbeam information. The control or signaling channel information transmitted from the access terminal, after being decoded, may act as a broadband pilot for the reverse link.

Referring to FIG. 4 , a transmitter and receiver in a multiple access wireless communication system one embodiment is illustrated. At transmitter system 410 , traffic data for a number of data streams is provided from a data source 412 to a transmit (TX) data processor 414 . In an embodiment, each data stream is transmitted over a respective transmit antenna. TX data processor 414 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 414 applies beamforming weights to the symbols of the data streams based upon the user to which the symbols are being transmitted. In some embodiments, the beamforming weights may be generated based upon eigenbeam vectors generated at the receiver 402 and provided as feedback to the transmitter 400 . Further, in those cases of scheduled transmissions, the TX data processor 414 can select the packet format based upon rank information that is 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 on provided by processor 430 . As discussed above, in some embodiments, the packet format for one or more streams may be varied according to the rank information that is transmitted from the user.

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

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. N T modulated signals from transmitters 422 a through 422 t are then transmitted from N T antennas 424 a through 424 t , respectively.

At receiver system 450 , the transmitted modulated signals are received by N R antennas 452 a through 452 r and the received signal from each antenna 452 is provided to a respective receiver (RCVR) 454 . 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 N R received symbol streams from N R receivers 454 based on a particular receiver processing technique to provide N T “detected” symbol streams. The processing by RX data processor 460 is described in further detail below. Each detected symbol stream includes 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. The processing by RX data processor 460 is complementary to that performed by TX MIMO processor 420 and TX data processor 414 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 ratios (SNRs) of the detected symbol streams, and possibly other channel characteristics, and provides these quantities to a processor 470 . RX data processor 460 or processor 470 may further derive an estimate of the “operating” SNR for the system. Processor 470 then provides estimated channel state 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 operating SNR. The CSI is then processed by a TX data processor 438 , which also receives traffic data for a number of data streams from a data source 476 , modulated by a modulator 480 , conditioned by transmitters 454 a through 454 r , and transmitted back to transmitter system 410 .

In addition, processor 470 may calculate the eigenbeams experienced by the receiver 402 . The eigenbeams may be calculated as discussed with respect to FIG. 3 . The processor 470 may then determine the dominant eigenbeams and feedback may only be provided for them. Processor 470 can quantize the dominant eigenbeams according to a codebook that is known are transmitter 400 . In some embodiments, as described with respect to FIG. 3 five-bit codes may be utilized allowing a wide range of feedback. The codebook size can vary depending on the reverse link resources available for such feedback.

In order to determine when to feedback the dominant eigenbeams, processor 470 may calculate channel statistics and determine what the change was in the channel statistics between two or more consecutive transmissions to the receiver 402 . Depending on the degree of change, a decision may be made as to whether to provide eigenbeam feedback. In additional embodiments, the processor may determine instantaneous channel information for a particular transmission and then determine a change between instantaneous channel information for one or more prior transmissions. This information may them be utilized to determine whether to provide eigenbeam feedback.

At transmitter system 410 , the modulated signals from receiver system 450 are received by antennas 424 , conditioned by receivers 422 , demodulated by a demodulator 440 , and processed by a RX data processor 442 to recover the CSI reported by the receiver system. 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 414 and TX MIMO processor 420 .

At the receiver, various processing techniques may be used to process the N R received signals to detect the N T transmitted symbol streams. These receiver processing techniques may be grouped into two primary 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 technique (which is also referred to as “successive interference cancellation” or “successive cancellation” receiver processing technique).

A MIMO channel formed by the N T transmit and N R receive antennas may be decomposed into N S independent channels, with N S ≦min {N T , N R }. Each of the N S 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 S =N T <N R , an independent data stream may be transmitted from each of the N T 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. Moreover, in those cases that successive interference cancellation processing is used at the receiver to recover the transmitted data streams, and then different SNRs may be achieved for the data streams depending on the specific order in which the data streams are recovered. Consequently, different data rates may be supported by different data streams, depending on their achieved SNRs. Since the channel conditions typically vary with time, the data rate supported by each data stream also varies with time.

The MIMO design may have two modes of operation, single code word (SCW) and multiple-code word (MCW). In MCW mode, the transmitter can encode the data transmitted on each spatial layer independently, possibly with different rates. The receiver employs a successive interference cancellation (SIC) algorithm which works as follows: decode the first layer, and then subtract its contribution from the received signal after re-encoding and multiplying the encoded first layer with an “estimated channel,” then decode the second layer and so on. This “onion-peeling” approach means that each successively decoded layer sees increasing SNR and hence can support higher rates. In the absence of error-propagation, MCW design with SIC achieves maximum system transmission capacity based upon the channel conditions. The disadvantage of this design arise from the burden of “managing” the rates of each spatial later (a) increased CQI feedback (one CQI for each layer needs to be provided); (b) increased acknowledgement (ACK) or negative acknowledgement (NACK) messaging (one for each layer); (c) complications in Hybrid ARQ (HARQ) since each layer can terminate at different transmissions; (d) performance sensitivity of SIC to channel estimation errors with increased Doppler, and/or low SNR; and (e) increased decoding latency requirements since each successive layer cannot be decoded until prior layers are decoded.

In a SCW mode design, the transmitter encodes the data transmitted on each spatial layer with “identical data rates.” The receiver can employ a low complexity linear receiver such as a Minimum Mean Square Solution (MMSE) or Zero Frequency (ZF) receiver, or non-linear receivers such as QRM, for each tone. This allows reporting of the channel estimates by the receiver to be for only the “best” layer and reduced transmission overhead for providing this information.

While FIG. 4 and the associated discussion refers to a MIMO system, other systems multi-input single-input (MISO) and single-output multi-input (SIMO) may also utilize the structures of FIG. 4 and the structures, methods and systems discussed with respect to FIG. 3 .

Referring to FIG. 5 , a block diagram of a transmitter system in a multiple access wireless communication system according to one embodiment is illustrated. Transmitter 500 , based upon channel information, utilizes rate prediction block 502 which controls a single-input single-output (SISO) encoder 504 to generate an information stream.

Bits 506 are turbo-encoded by encoder block 506 and mapped to modulation symbols by mapping block 508 depending on the packet format (PF) 524 , specified by a rate prediction block 502 . The coded symbols are then de-multiplexed by a demultiplexer 510 to M layers 512 , which are provided to a beamforming module 514 .

Beamforming module 514 generates an N T ×M beamforming matrix. The matrix may be formed for each transmission on the reverse link. Each transmission may involve processes M layers and generate N T streams. The eigen-beam weights may be generated from the eigenbeam feedback 524 , e.g. quantized eigenvectors, transmitted by the access terminal to the access point. Further, as described above the feedback may comprise only the dominant eigenvectors experienced at the access terminal.

The N T streams 512 after beamforming are provided to OFDM modulators 518 a to 518 t that interleave the output symbol streams with pilot symbols. The OFDM processing for each transmit antenna 520 a to 520 t then in an identical fashion, after which the signals are transmitted via a MIMO scheme.

In SISO encoder 504 , turbo encoder 506 encodes the data stream, and in an embodiment uses 1/5 encoding rate. It should be noted that other types of encoders and encoding rates may be utilized. Symbol encoder 508 maps the encoded data into the constellation symbols for transmission. In one embodiment, the constellations may be Quadrature-Amplitude constellations. While a SISO encoder is described herein, other encoder types including MIMO encoders may be utilized.

Rate prediction block 502 processes the CQI and/or channel estimate information, including rank information, which is received at the access point for each access terminal. The rank information may be provided based upon broadband pilot symbols, hop based pilot symbols, or both. The rank information is utilized to determine a modulation rate by rate prediction block 502 . In an embodiment, the rate prediction algorithm may use a 5-bit CQI feedback 522 approximately every 5 milliseconds and/or channel estimates. The actual number of bits of CQI feedback 22 may vary based upon design choices or parameters.

The packet format, e.g. modulation rate, is determined using several techniques. Exemplary techniques are depicted and disclosed in co-pending U.S. patent application Ser. No. 11/021,791, entitled “Performance Based Rank Prediction for MIMO Design,” and U.S. patent application Ser. No. 11/022,347, entitled “Capacity Based Rank Prediction for MIMO Design,” both of which are incorporated herein by reference as if set forth in their entireties.

Referring to FIG. 6 , a block diagram of a receiver system in a multiple access wireless communication system according to one embodiment is illustrated. In FIG. 6 , each antenna 602 a through 602 t receives one or more symbols intended for the receiver 600 . The antennas 602 a through 602 t are each coupled to OFDM demodulators 604 a to 604 t , each of which is coupled to hop buffer 606 . The OFDM demodulators 704 a to 604 t each demodulate the OFDM received symbols into received symbol streams. Hop buffer 606 stores the received symbols for the hop region in which they were transmitted.

The output of hop buffer 606 is provided to a decoder 608 , which may be a decoder that independently processes each carrier frequency of the OFDM band. Both hop buffer 606 and the decoder 608 are coupled to a channel statistics processing 610 that also forms the eigenbeamweights that can be provided to the transmitter for future transmissions. In addition, channel statistics processing 610 determines channel statistics, second order channel statistics, instantaneous channel information, or signal-to-noise ratios for multiple transmissions. The channel statistics processing 610 can also determine whether changes have occurred and then transmit the eigenbeam feedback. In addition, receiver 600 may determine the available reverse link resources,

The demodulated information streams are then provided to Log-Likelihood-Ratio block 612 and decoder 614 , which may be a turbo decoder or other decoder to match the encoder used at the access point, that provide a decoded data stream for processing.

Referring to FIG. 7 , a flow chart of determining resources to be allocated for providing eigenbeam feedback according to an embodiment is illustrated. A determination is made as to the available reverse link resources, block 700 . The resources may be the number of symbols that may be transmitted over a reverse link signaling or control channel, the available bandwidth, or other information. This determination may be made at an access point and provided to the access terminal or at the access terminal based upon fixed parameters or data rates for the next forward link transmission.

A determination is then made as to the amount of eigenbeam feedback that is available at the access terminal, block 702 . The amount may be the total number of eigenbeams, the number of dominant eigenbeams, or a ranking of the eigenbeams. Further, the amount may include rank information or CQI information so that the amount takes into account all or most of the feedback required from the access terminal.

An indicator as to the resources allocated for reverse link transmission is generated, block 704 . The indicator may be generated at either the access point or access terminal and then transmitted to the access terminal. Resources on the reverse link are then allocated for transmission based upon the indicator, block 706 .

Referring to FIG. 8 , a flow chart of determining whether to provide eigenbeam feedback according to another embodiment is illustrated. Channel information is generated, block 800 . The channel information may be instantaneous channel information or channel statistics. In some embodiments, the channel information may relate to the packet error rate, fading, signal strength, channel state information or other information. Further, the channel information calculated in either, or both, the frequency and time domain may be utilized. Further, in some embodiments, second order channel statistics are utilized. In other embodiments, first order or higher order channel statistics are utilized in addition to, or in lieu of, the second order channel statistics. In some embodiments, the channel information may be calculated based upon pilot symbols or both pilot symbols and data symbols.

The change in channel information is determined, block 802 . The change may be between consecutive transmissions, between the current transmission and a transmission N transmissions prior to the current transmission, time averaged changes, averages over M transmissions, or other approaches. In one embodiment, the changes may be calculated as the absolute value of the difference of the squares of the channel information for the current transmission and a transmission that is N transmissions prior to the current transmission.

A determination is made whether a channel between an access terminal and access point is stationary or variable, block 804 . In an embodiment, this determination may be made based upon if the change in channel statistics is above or below a threshold. In other embodiments, the determination may be based on a rate of change between several determinations of the change of the channel information. Other approaches may also be utilized to determine whether the channel is stationary or variable.

In the case where the channel is determined to be stationary, the dominant eigenbeams are determined, block 806 . Information regarding the dominant eigenbeams is then transmitted to the access point, block 808 . The information regarding the dominant eigenbeams may be quantized according to a codebook. Also, it should be noted that block 806 may occur at any time prior to block 804 and may be independent of the process depicted in FIG. 8 . In the case where the channel is determined to be variable, no feedback is provided, block 810 .

Referring to FIG. 9 , a flow chart of generating eigenbeam vectors according to a further embodiment is illustrated. The eigenbeam information provided from the terminal to the access point is read, block 900 . As discussed previously, in some embodiments, the eigenbeam information may be quantized and therefore the appropriate information is read from a codebook for use at block 900 . Further, the eigenbeam information may apply to only the dominant eigenbeams.

The eigenbeam information is utilized to construct an eigenbeamforming matrix, block 902 . The eigenbeamforming matrix is then decomposed, block 904 . The decomposition may be a QR decomposition. The eigenvectors representing the beamforming weights can then be generated for the symbols of the next hop region to be transmitted to the access terminal, block 906 .

Referring to FIG. 10 , a flow chart of generating eigenbeam feedback according an embodiment is illustrated. The forward link channel is estimated based upon received symbols, such as pilot symbols, block 1000 . The dominant eigenbeams are then determined and calculated based upon the forward link channel estimate, block 1002 . A determination is made as to the amount of available reverse link resources, block 1004 . The resources may be the number of symbols that may be transmitted over a reverse link signaling or control channel, the available bandwidth, or other information. This determination may be made at an access point and provided to the access terminal or at the access terminal based upon fixed parameters or data rates for the next forward link transmission.

In the case where the reverse link resources are considered low, a frequency average of the dominant eigenbeams are determined, prior to being provided as feedback to the access point, block 1006 . In the case where the reverse link resources are considered high, the dominant eigenbeams for each required frequency are provided as feedback to the access point, block 1008 .

The above processes may be performed utilizing TX processor 420 or 460 , processor 430 or 470 , and memory 432 or 472 . Further processes, operations, and features described with respect to FIGS. 5A , 5 B, and 6 - 10 may be performed on any processor, controller, and/or other processing device and may be stored as computer readable instructions in a computer readable medium as source code, object code, or otherwise.

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 a access point or a 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 their spirit or scope. Thus, the present disclosure 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.