HK1136705B - Beamspace-time coding based on channel quality feedback - Google Patents

Description

Beam space time coding based on channel quality feedback

Claiming priority in accordance with 35U.S.C. § 119

This patent application claims priority from a provisional patent application entitled "BEAMSPACE-TIMECODING BASE CHANNEL QUALITY FEEDBACK" number 60/870,654, filed 2006, 12/19/2006, which is assigned to the assignee of the present application and which is expressly incorporated herein by reference.

Background

Wireless communication devices may operate in a variety of operating conditions and operating environments. Depending on the location of the mobile wireless device relative to the source of the signal transmission, the mobile wireless device may experience a dramatic change in signal quality. The change in signal quality can be characterized by a change in the wireless channel connecting the transmitter and the wireless receiver.

There are many factors that can affect the wireless channel. For example, the received signal strength decreases as the distance between the transmitter and the receiver increases. In addition, changes in terrain and the presence of obstacles and reflective surfaces can result in the formation of multipath. Signals traveling from a transmitter to a receiver through multiple signal paths may combine additively or destructively. By way of example, destructive signal combining caused by phase rotation in multipath signal components can result in a significant reduction in signal quality at the receiver. The degradation of signal quality is commonly referred to as signal fading or simply fading.

Wireless communication systems may implement a variety of techniques to reduce the probability of operating in deep fades. Wireless communication systems may implement signal diversity to compensate for fading. Diversity generally refers to implementing some type of redundancy to provide or eliminate independent signal paths.

The transmitter may provide diversity by introducing different distinguishable signals to increase the probability that the receiver will receive and distinguish the transmitted signal. The transmitter may introduce diversity by using multiple transmit antennas, multiple transmit frequencies, multiple transmit times, or some combination thereof.

Diversity can be achieved, for example, by transmitting the original information symbol from one antenna and a modified version of the symbol from a second antenna. A modified version of the original signal may refer to a delayed, conjugate, inverted, rotated version of the original signal, the like, or a combination of some or all of the above. A rotated signal refers to a complex rotation of the phase of a signal relative to a reference signal. The receiver processes the entire received signal over one or more symbol periods to recover the transmitted symbols.

Similarly, a receiver may provide some amount of diversity by using multiple receive antennas for spatial diversity. Preferably, by spacing the plurality of receive antennas apart by a distance, each antenna may be enabled to experience channel characteristics that are independent of the channel experienced by the other receive antennas.

Disclosure of Invention

The present invention provides methods and apparatus for improving diversity gain at a receiver by applying beamforming to space-time coded signals for transmit diversity. The transmit signal is space-time coded over a plurality of space-time antenna groups, where each space-time antenna group is associated with a particular space-time code. The signals on each space-time antenna group are beamformed over multiple antennas in the space-time antenna group. Each of the plurality of antennas in a space-time antenna group is weighted with a different weight than the other antennas in the space-time antenna group. The beamforming weights may be changed based on a channel quality feedback indication from the receiver. The magnitude, phase or combination of magnitude and phase of each weight or a vector of weights may be varied in dependence on the channel quality indication to improve the quality of the received signal.

Some aspects of the present disclosure include a method for providing transmit diversity. The method comprises the following steps: generating a plurality of space-time coded signals according to the transmission signal; receiving a channel quality indication; generating at least one weight vector according to the channel quality indication; beamforming at least one of the plurality of space-time coded signals using a corresponding one of the at least one weight vector.

Some aspects of the present disclosure include a method for providing transmit diversity. The method comprises the following steps: generating a plurality of space-time coded signals according to the transmission signal; receiving a channel quality indication; beamforming each of the space-time coded signals using a corresponding weight vector, wherein at least one weight vector is determined in part from the channel quality indication.

Some aspects of the present disclosure include a method for optimizing transmit diversity. The method comprises the following steps: receiving a plurality of signals, each of the plurality of signals being received in a corresponding signal beam; determining a channel estimate for each signal beam; determining a channel quality indication from the channel estimate; transmitting the channel quality indication as feedback information to a transmission source of the signal beam.

Some aspects of the present disclosure include an apparatus for providing transmit diversity, the apparatus comprising: a transmitter for generating a transmit signal stream; a transmit diversity encoder for receiving the transmit signal stream and generating a plurality (G) of transmit diversity/space-time coded transmit streams from the transmit signal stream; a weight matrix generator for receiving a channel quality indication and generating at least one weight vector of a set of weight vectors in dependence on the channel quality indication; a plurality of beamforming encoders, each of the plurality of beamforming encoders to receive one of the plurality of transmit diversity/space-time coded transmit streams and to generate a plurality (K) of weighted sub-streams to beamform the one of the plurality of transmit diversity/space-time coded transmit streams according to a weight vector of the set of weight vectors.

Some aspects of the present disclosure include an apparatus for providing transmit diversity, the apparatus comprising: a receiver for receiving a plurality of space-time coded transmit signals in a plurality of beams, wherein each space-time coded transmit signal is transmitted in a different beam; a pilot extraction module, coupled to the receiver, for extracting at least one pilot signal from each beam; a channel estimation module, coupled to the pilot extraction module, for determining a channel estimate for each of the plurality of beams from the at least one pilot signal; a channel quality indication generator for determining a channel quality indication from the channel estimate; a transmitter configured to generate a feedback message including the channel quality indication and transmit the feedback message to a source of the space-time coded transmit signal.

Drawings

The features, objects, and advantages of embodiments of the present disclosure will become apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like elements have like reference numerals.

Fig. 1 is a simplified functional block diagram of an embodiment of a wireless communication system.

Fig. 2 is a simplified functional block diagram of an embodiment of a transmitter and receiver in a multiple access wireless communication system.

Fig. 3 is a simplified functional block diagram of an embodiment of a transmitter system with beamformed space-time coding transmit diversity.

Fig. 4 is a simplified functional block diagram of an embodiment of a transmitter system with beamformed space-time coding transmit diversity.

Fig. 5 is an example of a beamforming weight constellation.

Fig. 6 is a simplified functional block diagram of an embodiment of a receiver for generating a channel quality indication from a beamformed space-time coded received signal.

Fig. 7 is a simplified flow diagram of an embodiment of a method for providing transmit diversity using beamformed transmit diversity/space-time coding.

Fig. 8 is a simplified flowchart of an embodiment of a method for generating feedback information from beamformed transmit diversity/space-time coded signals.

Fig. 9 is a simplified functional block diagram of an embodiment of a transmitter system with beamformed space-time coding transmit diversity.

Fig. 10 is a simplified functional block diagram of an embodiment of a receiver for generating a channel quality indication from a beamformed space-time coded received signal.

Detailed Description

Methods and apparatus for generating and transmitting wireless signals that combine the benefits of transmit diversity/space-time coding and beamforming are described. The transmitter has N transmit antennas. The N transmit antennas are divided into G antenna groups, where G ≦ N. In each antenna group, by a weight vector w_g＝[w_g1 w_g2…w_g，N/G]The antennas are weighted to form beams.

The information stream to be transmitted is first diversity/space-time coded into G substreams. Each sub-stream is beamformed and transmitted using one antenna group. The transmitter may optimize the weights applied by the weight vector based on feedback provided by the receiver.

The receiver processes the signals received from the beamformed substreams and generates a Channel Quality Indication (CQI) value from the processed substreams. The receiver may independently generate a channel quality indication from the signal from each beamformed substream or from the quality of the composite signal. The receiver may transmit one or more CQI values to the transmitter in a feedback message or via some other communication link. For example, the receiver may generate a CQI value based on a pilot signal transmitted by the transmitter.

The transmitter, or more specifically the transmitter in communication with the receiver, may receive the CQI value from the receiver. The transmitter may adjust the beamforming weights applied to one or more of the substreams based on the CQI value. The transmitter may also receive one or more metrics indicative of downlink interference caused by signals corresponding to a particular access terminal. For example, the downlink interference metric can be determined by one or more receivers in an access terminal for which the transmitter signal is not optimized, or by one or more receivers located at other access points. The transmitter independently adjusts the weights in each sub-stream to maximize the signal quality at the receiver; the transmitter may also adjust the weights of the multiple sub-streams to maximize signal quality at the receiver; the transmitter may also minimize the inter-cell interference experienced in other cells or coverage areas while adjusting the weights in each sub-stream to improve signal quality at the receiver; the transmitter may also perform a combination of the above operations. The transmitter may be arranged to select among a predetermined grid of weights, or may be arranged to vary the magnitude and/or phase of one or more individual weights continuously.

Fig. 1 is a simplified functional block diagram of an embodiment of a multiple access wireless communication system 100. The multiple access wireless communication system 100 includes a plurality of cells, such as cells 102, 104, and 106. In the embodiment of fig. 1, each of cells 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 cell 102, each of antenna groups 112, 114, and 116 corresponds to a different sector. For example, cell 102 is partitioned into three sectors 120a-102 c. A first antenna 112 serves a first sector 102a, a second antenna 114 serves a second sector 102b, and a third antenna 116 serves a third sector 102 c. In cell 104, each of antenna groups 118, 120, and 122 corresponds to a different sector. In cell 106, each of antenna groups 124, 126, and 128 corresponds to a different sector.

Each cell or each sector of a cell is configured to support or serve a number of access terminals that are in communication with one or more sectors of a corresponding 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. Although each of the access points 142, 144, and 146 are shown as communicating with two access terminals, each of the access points 142, 144, and 146 is not limited to communicating with two access terminals and may support any number of access terminals up to the limits imposed by the physical limitations or by the communications standards.

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 (AT) may also be referred to as and include some or all the functionality of a User Equipment (UE), a user terminal, a wireless communication device, a terminal, a mobile station, a subscriber station, or some other terminology.

As can be seen in fig. 1, each of the access terminals 130, 132, 134, 136, 138, and 140 is located in a different portion of the respective cell than other access terminals in the same cell. Further, each access point may be a different distance from the antenna group corresponding to the access point with which it communicates. These two factors provide additional circumstances that result in different channel conditions between each access terminal and the antenna group corresponding to the access point with which it communicates, in addition to cell environment and other conditions.

Each access terminal (e.g., 130) typically experiences unique channel characteristics that are not experienced by any other access terminal due to variations in channel conditions. In addition, channel characteristics change over time and change due to changes in access terminal location.

The access points 142, 144, and 146 may implement space-time coding transmit diversity to mitigate some of the effects of signal quality fading that may be caused, in part, by changes in channel conditions. The access points 142, 144, and 146 are used to generate a plurality of different space-time coded sub-streams. The access points 142, 144, and 146 are also used to beamform each of the different space-time coded sub-streams. Each substream at each of the access points 142, 144, and 146 may then be transmitted in a beamformed manner using multiple antennas. Each space-time coded and beamformed sub-stream may be received at an access terminal 130, 132, 134, 136, 138, and 140 after passing through substantially uncorrelated channel conditions. Such operation improves the ability of access terminals 130, 132, 134, 136, 138, and 140 to receive signals under various operating conditions and minimizes the probability that access terminals 130, 132, 134, 136, 138, and 140 will be unable to maintain communication with the serving access point due to experiencing channel fading conditions.

The access points 142, 144, and 146 may beamform the sub-streams by weighting each of the signals coupled to the corresponding multiple antennas with a weight. Each space-time coded substream is decomposed or divided into a number of copies and the number of copies is weighted using a weight vector having the same dimension as the number of copies.

The access points 142, 144, and 146 can use feedback from each access terminal (e.g., 130) to optimize the weights applied to one or more of the sub-streams. Access points 142, 144, and 146 can transmit pilot signals that are not beamformed or beamformed with known weight vectors to aid in channel analysis by access terminals 130, 132, 134, 136, 138, and 140. The pilot signal may be one or more known signals transmitted in periodic time, frequency, or a combination of time and frequency. In other embodiments, the pilot signal is not periodic, but is transmitted according to a predetermined algorithm. For example, the pilot signals may be scheduled pseudo-randomly, while the access terminals 130, 132, 134, 136, 138, and 140 have the ability to predict the location and time of occurrence of the pilot signals. In another example, the access points 142, 144, and 146 can schedule pilot signals at the request of one or more terminals (e.g., 130).

Each terminal (e.g., 130) may receive pilot signals from its serving access point 142 and perform channel estimation for each independent substream. If the access point is beamforming the pilot substream, the access terminal 130 may compensate for the predetermined beamforming weights applied to the pilot substream in estimating the channel.

The access terminal 130 generates a Channel Quality Indication (CQI) value based on the channel estimate. In one embodiment, the access terminal 130 generates a CQI value representing a channel estimate for each substream. In another embodiment, the access terminal 130 generates a CQI value based on a combination of multiple channel estimates.

Access terminal 130 may generate a CQI value representing the channel estimate and may also generate a CQI value indicating the variance of the channel estimate. For example, the access terminal 130 may generate a CQI value that merely indicates whether the composite signal quality is improved or degraded relative to existing channel estimates. In another embodiment, the access terminal 130 generates a CQI value for each channel estimate, the CQI value representing the magnitude of the channel estimate.

Access terminal 130 generates a feedback message with one or more CQI values and transmits the CQI values back to the access point corresponding to the pilot signal used to generate the CQI values.

The access point (e.g., 142) may also receive one or more estimates of downlink interference. For example, an access terminal (e.g., 132) from another sector or an access terminal (e.g., 140) from another cell may estimate the level of downlink interference generated by beamformed signals from some other sector 120c or cell 120. Alternatively, a receiver (e.g., 146) at an access point may estimate downlink interference generated at another access point (e.g., 142). The estimate of downlink interference may be sent to the access point 142, assuming that the access point 142 is the source of the interference.

The access point (e.g., 142) receives the CQI value and the downlink interference estimate and adjusts the weights of the beamforming weight vector to improve channel quality at the access terminal 130, which may also be adjusted to simultaneously reduce downlink interference experienced in other cells or sectors. The access point 142 may optimize the beamforming weights for each beamformed substream. The access point 142 may vary the beamforming weights according to a predetermined algorithm, for example, the access point 142 may vary the weights continuously by a predetermined incremental value or by selecting a weight from a predetermined set of weights. The access point 142 may vary the magnitude, phase, or combination of magnitude and phase of the weights.

As shown in fig. 2, the above-described embodiments may be implemented using Transmit (TX) processor 220 or 260, processor 230 or 270, and memory 232 or 272. The processes may be performed on any processor, controller or other processing device, and may be stored as computer readable instructions in source code, object code, or other form in a computer readable medium.

Fig. 2 is a simplified functional block diagram of an embodiment of a transmitter and receiver in a multiple access wireless communication system 200. At the transmitter system 210, traffic data for a number of data streams is provided from a data source 212 to a Transmit (TX) data processor 214. In one embodiment, each data stream is transmitted over a respective transmit antenna. TX data processor 214 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 214 applies space-time coding and beamforming weights to the symbols of the data streams and to the antennas used to transmit the symbols, depending on the user to which the symbols are being transmitted. In some embodiments, the beamforming weights may be generated from channel response information indicating the conditions of the transmission path between the access point and the access terminal. Further, in those cases where transmissions are scheduled, TX data processor 214 may make a selection of a packet format based on rank (rank) information sent by 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 modulated (e.g., symbol mapped) based on a particular modulation scheme (e.g., BPSK, QPSK, 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 provided by processor 230. In some embodiments, the number of parallel spatial streams may vary depending on the rank information sent by the user.

The modulation symbols for all data streams are then provided to a TX MIMO processor 220, which TX MIMO processor 220 may further process the modulation symbols (e.g., for OFDM). The TXMMIMO processor 220 then forwards the data to N_TA plurality of transmitters (TMTR)222a through 222t provide N_TA stream of modulation symbols. TX MIMO processor using channel response information of users220 apply beamforming weights to the symbols of the data stream and to the antenna used to transmit the symbol, depending on the user to which the symbols of the data stream are to be transmitted.

Each transmitter 222a through 222t 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. Then respectively from N_TN transmitted from transmitters 222a through 222t by antennas 224a through 224t_TA modulated signal.

Transmitter system 210 may also be used to receive signals from one or more antennas 224a through 224 t. The corresponding receivers 223a to 223t receive and process the received signals. Each of the receivers 223a to 223t may be configured to amplify, filter, and frequency convert a received signal corresponding thereto to a baseband signal, the receivers 223a to 223t also being coupled to the demodulator 240.

Demodulator 240 may demodulate the received signal to recover the received signal and information. The output of demodulator 240 is coupled to a RX data processor 242. RX data processor 242 may be used to extract various information elements contained in the received signal. Some of the information may be overhead information used by transmitter system 210 and other information may be user data that may be processed for output to a user or other destination device (not shown) via a data sink 244.

The overhead information may include CQI values generated by receiver system 250 and transmitted to transmitter system 210. RX data processor 242 provides a CQI value or a message with a CQI value to processor 230. Processor 230 operates in conjunction with executable code stored in memory 232 to determine from received CQI values changes made to beamforming weights applied to the signal substreams at TX data processor 214 or TX MIMO processor 220.

At receiver system 250, N may be passed_REach antenna 252a through 252r receives the transmitted modulated signal and provides a received signal from each antenna 252 to a respective receiver (RCVR) 254. Each receiver 254 may condition (e.g., filter, amplify, and downconvert) a respective received signal, digitize the conditioned signal to provide samples, and further process the samples to provide a corresponding "received" symbol stream.

RX data processor 260 then proceeds from N according to a particular receiver processing technique_RA receiver 254 receives the symbol stream and receives N_RThe symbol streams are processed to provide a rank-valued number of "detected" symbol streams. The processing by RX data processor 260 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. The RX data processor 260 then demodulates, deinterleaves, and decodes each detected symbol stream to recover the traffic data for the data stream. The processing by RX data processor 260 is complementary to that performed by TX MIMO processor 220 and TX data processor 214 at transmitter system 210.

The channel response estimate generated by RX processor 260 may be used to perform spatial and spatial/temporal processing at the receiver, adjust power levels, change modulation rates and modulation schemes, or other operations. RX data processor 260 may further estimate the signal-to-noise ratios (SNRs) of the detected symbol streams, and possibly other channel characteristics, and provide these quantities to a processor 270.

In conjunction with executable code stored in memory 272, processor 270 may generate one or more CQI values based on the channel estimates. Processor 270 may also access one or more stored CQI values corresponding to the earlier channel interference stored in memory 270 when generating the current CQI value. Processor 270 couples one or more CQI values to TX data processor 278.

The TX data processor 278 formats CQI values to be transmitted back to the transmitter system 210. For example, TX data processor 278 may generate one or more feedback messages that include CQI values. The TX data processor 278 couples the feedback message to a modulator 280, which modulator 280 modulates the message according to a predetermined format. The modulated messages are provided to one or more transmitters 255a-255r, where the modulated feedback messages are upconverted and transmitted back to transmitter system 210.

At the receiver, N may be processed using various processing techniques_RA received signal to detect N_TA transmitted symbol stream. These receiver processing techniques can be divided into two broad categories: (i) spatial and space-time receiver processing techniques (which are also referred to as equalization techniques); (ii) "successive zero forcing/equalization and interference cancellation" receiver processing techniques (which are also referred to as "successive interference cancellation" or "successive cancellation" receiver processing techniques).

May be composed of N_TA transmitting antenna and N_RThe MIMO channel formed by the receiving antennas is decomposed into N_SA separate channel of which N_S≤min{N_T，N_R}。N_SEach of the independent channels may be referred to as a spatial subchannel (or a transmission channel) of the MIMO channel, and one spatial subchannel corresponds to one dimension.

Fig. 3 is a simplified functional block diagram of an embodiment of a transmitter system 300 for implementing beamforming of space-time encoded signals, wherein beamforming weights are optimized using CQI feedback from a receiver. The simplified functional block diagram of fig. 3 is limited to only the portion of the transmitter system that is associated with beamforming the space-time encoded signal. Other parts of the transmitter system have been omitted for the sake of brevity and clarity. Transmitter system 300 may be integrated into, for example, an access point of the communication system of fig. 1 and may be an embodiment of the transmitter system of fig. 2.

Transmitter system 300 includes a transmitter 310 coupled to a transmit diversity/space-time encoder 320. Transmit diversity/space-time encoder 320 couples the plurality of encoded signals to a plurality of beamforming encoders330₀-330_G. Beamforming encoder 330₀-330_GCoupling beamformed signals to multiple antennas 340₀₀-340_GK. The timing and synchronization module 350 is coupled to a weight matrix generator 360, the weight matrix generator 360 being coupled to the plurality of beamforming encoders 330₀-330_G。

The transmitter 310 is used to process the samples to generate a modulated signal stream. For example, the transmitter 310 may be configured to generate a number of samples of an Orthogonal Frequency Division Multiplexing (OFDM) symbol from a number of information bits. The transmitter 310 may be configured to map information bits to subcarriers of an OFDM symbol and modulate the information bits onto the subcarriers according to a predetermined modulation format. The transmitter 310 may frequency convert the OFDM symbols to a desired RF transmission frequency. In this embodiment, the output of the transmitter 310 is a serial signal stream of OFDM symbol samples at the desired RF transmission frequency.

The output of the transmitter 310 is coupled to a time diversity/space-time encoder 320. Time diversity/space-time encoder 320 is used to divide the symbol stream from transmitter 310 into multiple (G) signal streams, which may also be referred to as substreams. The time diversity/space-time encoder 320 operates on multiple signal streams to produce modified versions of the signal streams. For example, time diversity/space-time encoder 320 may be used to deliver one substantially unmodified symbol stream and modify each of the remaining G-1 signal streams. In general, a signal stream may be considered unmodified, since all signal streams may be normalized to a particular signal stream.

Time diversity/space-time encoder 320 may be used to perform operations such as delaying, inverting, conjugating, rotating, etc., or a combination thereof, on each of the G-1 signal streams. The time diversity/space-time encoder 320 may introduce delay for a particular signal stream using variable delays, delay lines, tapped delay lines, digital delays, etc., or some combination of delay elements. For example, time diversity/space-time encoder 320 may be used to invert the signal stream using an inverting amplifier. As another example, time diversity/space-time encoder 320 may be used to conjugate the signal stream using a rotator, an inverter coupled to a quadrature phase signal component, or the like, or a combination thereof. Additionally, time diversity/space-time encoder 320 may be used to rotate the signal stream using one or more multipliers operating on either the in-phase or quadrature signal components, one or more multipliers weighting the phase components, delay elements, etc., or some combination of the above.

In general, time diversity/space-time encoder 320 performs different modifications on each signal stream, such that transmit diversity can be achieved by transmitting G signal streams on G different antennas. In a typical time diversity/space-time coding system, the G antennas are spatially separated. In the embodiment of fig. 3, additional processing is performed for each of the G different time diversity/space-time coded signal streams. Another way to provide diversity gain at the receiver is to use transmit beamforming, where the same information symbol is transmitted from multiple antennas. The signals from each of the multiple antennas may be weighted differently to maximize the overall signal-to-noise ratio at the receiver. The different weighting of the signals may be achieved by using different antenna gains or by weighting the individual signals coupled to each antenna. Although the weighting of the signals is shown immediately before the antennas, the beamforming weighting may also be performed earlier in the transmission chain, and additionally may also be performed by operating on the signal streams using time-domain weighting or frequency-domain weighting of the signals.

In the embodiment of fig. 3, multiple antennas are used to independently beamform each of the G signal substreams. Coupling each of the different signal substreams from the time diversity/space-time encoder 320 to multiple beamforming encoders 330₀-330_G. Beamforming encoder 330₀-330_GCorresponding to the number of transmit diversity signal streams generated by the time diversity/space-time encoder 320.

Each beamforming encoder (e.g., 330)₀) May be used to generate a plurality of weighted signal streams, each weighted signal stream being applied to a corresponding antenna. Each beamforming encoder (e.g., 330)₀) One of the multiple signal streams is received from the transmit diversity/space-time encoder 320. Beamforming encoder 330₀The signal is split into K replicated signal streams and each of the K replicated signal streams is weighted with an associated beamforming weight. Beamforming encoder 330₀Coupling the weighted signal streams to a particular beamforming encoder 330₀Associated K antennas 330₀₀-330_0K。

Thus, the total number of antennas is equal to the number G of time diversity/space-time coded groups or substreams multiplied by the number K of beamformed signal streams generated for each time diversity/space-time coded group. In the embodiment of fig. 3, there are a total of N × G × K antennas. The embodiment of transmitter system 300 in fig. 3 shows each time diversity/space-time signal having the same number of beamformed signal streams. However, in other embodiments, different time diversity/space-time signals may have different beamforming dimensions.

The weight matrix generator 360 is used to generate the weight matrix for the beamforming encoder 330₀-330_GEach encodes the weight vector used. Each vector in the weight matrix corresponds to a beamforming encoder (e.g., 330)₀). In general, each weight vector is different, but the weight vectors are not required to be different.

Each weight w in the weight vector has an associated amplitude a and phase rotationThe weight matrix generator 360 may be used to generate fixed weight matrices and may also be used to generate variable weight matrices. In some embodiments, weight matrix generator 360 may be used to generate a combination of fixed and variable weight matrices. The weight matrix generator 360 may be used to change the weights based on, for example, time, events, or a combination of time and events.

If estimates of the channels from the transmit antennas to the receiver are available at the transmitter, the weight matrix generator 360 may determine an optimal value for the weights in each weight vector to maximize the signal-to-noise ratio (SNR) or some other metric related to the received signal quality. Transmitter system 300 need not have knowledge of the actual channel estimate, but may be operating with some other signal metric that is derived from or related to the received signal quality or channel estimate.

Weight matrix generator 360 can be utilized to generate a plurality of weight vectors based on information provided to transmitter system 300 by a receiving device (e.g., an access terminal). In the embodiment shown in fig. 3, transmitter system 300 may be used to receive feedback information from a wireless link.

The transmitter system includes a receive antenna 370 that may be used to receive signals transmitted by an access terminal (not shown). Although a different receive antenna 370 is depicted in the present embodiment, transmitter system 300 may use multiple receive antennas or use the same antenna for both transmission and reception. Thus, in some embodiments, there is no dedicated receive antenna 370. But instead one or more of the antennas 340 are used as receive antennas.

The receive antenna 370 couples the received signal to a receiver 380, and the receiver 380 operates to amplify, filter, and frequency convert the received signal to a signal for further processing. In general, receiver 380 operates to output a baseband signal with received correlation information that includes CQI values generated by one or more access terminals.

Receiver 380 couples an output signal to CQI processor 390. CQI processor 390 operates on the baseband signal from receiver 380 to recover CQI values transmitted by the access terminal. For example, CQI processor 390 may extract CQI values from a particular overhead message or a particular dedicated message. The CQI value may be, for example, a predetermined field in the message, or may be identified by using a predetermined header, prefix, or other identifier.

CQI processor 390 couples CQI values and the identity of the corresponding access terminal to weight matrix generator 360. The weight matrix generator 360 can modify beamforming weights or weight vectors or generate new beamforming weights or weight vectors based in part on CQI values reported by the receiving access terminal.

In a weight vector (e.g., w)_g＝[w_g1 w_g2…w_g，N/G]) Each weight may include a magnitude component and a phase component, e.g.,the weight matrix generator 360 may be used to introduce intentional time-variations in the weight vectors in a variety of ways. The weight matrix generator 360 may be used to vary the magnitude component, the phase component, or a combination thereof. Additionally, the weight matrix generator 360 may be used to vary the weights in any given weight vector independently, or according to a weight.

As an example, the weight matrix generator 360 can be utilized to actually maintain a constant magnitude component and vary the phase component based in part on information fed back from the access terminal to the transmitter. The weight matrix generator 360 may independently vary the phase components of the individual weights or may vary the second phase components of the phase components based on the first phase components.

For example, the weight matrix generator 360 may be used to maintain a substantially constant phaseThe magnitude component is varied in part based on information fed back from the access terminal to the transmitter. For example, the weight matrix generator 360 may hold φ₀And phi₁Constant and varying the first and second amplitude components. The weight matrix generator 360 may independently vary the magnitude component of the individual weights or may vary the magnitude component of the second magnitude component based on the first phase component. In another embodiment, the weight matrix generator 360 may be used to simultaneously vary the magnitude and phase components of at least some of the beamforming weights.

The rate at which the weight matrix generator 360 changes the required weight components may be fixed or may vary. The weight matrix generator 360 may be used to change the components based on the rate of CQI feedback, the passage of time, the occurrence of an event, or a combination of the above. In varying the multiple weight components, the weight matrix generator 360 may be used to use a separate rate for each varied component. Alternatively or additionally, the weight matrix generator 360 may be used to use the same rate or an independent rate for each vector in the weight matrix. In general, the weight matrix generator 360 may be used to vary individual weight components (or vary the rate of individual weight components) using a function that is completely independent for each component (or rate).

In one embodiment, the access terminal transmits the CQI value at a rate derived from the OFDM symbol rate. For example, transmitter system 300 can receive CQI values from access terminals and weight matrix generator 360 can change weights in a weight matrix for each frame, wherein the frame is comprised of a predetermined number of OFDM symbols. The weight matrix generator 360 may change the weight vector after receiving the CQI value, or the weight matrix generator 360 may update the weight vector according to a predetermined plurality of CQI values.

The timing and synchronization module 350 is used to synchronize the timing of the weight matrix generator 360 with the timing used in the transmitter 310. For example, the timing and synchronization module 350 may include a clock that is synchronized with the system time used by the transmitter 310 in generating the transmit stream. In one embodiment, the timing and synchronization module may be synchronized with the OFDM symbol timing of the transmit stream so that the weight matrix generator 360 may generate time varying weights that vary across symbol boundaries for transmission.

Beamforming encoder 330₀-330_GCan be used to weight the respective space-time coded sub-streams in both time domain and frequency domain operation. In embodiments where several access terminals are co-located or where transmitter system 300 dedicates OFDM symbols to a particular access terminal, it may be convenient to apply the weighting vectors to the sub-streams in the time domain. However, in embodiments where each OFDM symbol includes information for multiple access terminals corresponding to different CQI values, it may be convenient to apply the weights in the frequency domain so that different subcarriers may be weighted according to the channel conditions experienced by the receiving access terminal. The choice of whether to use the weight vector in the time or frequency domain is not limited by the use of CQI to optimize the beamforming weights. Generally, whether one domain or another is selected is determined by the processing power required to implement the various embodiments.

Fig. 4 is a simplified functional block diagram of an embodiment of a transmitter system 300 for beamforming. In the embodiment of fig. 4, transmitter system 300 is configured with a total of four antennas and is used to generate transmit diversity/space-time coding over two different groups. The embodiment of fig. 4 illustrates a particular embodiment of the generalized transmitter system shown in fig. 3.

In the embodiment of fig. 4, transmitter 310 is configured to generate a transmit stream, which may be, for example, a stream of multiple OFDM symbols converted to a transmit RF frequency. The transmitter 310 couples the transmit stream to a transmit diversity/space-time encoder 320.

The transmit diversity/space-time encoder 320 is used to generate a group of two encoded transmit streams from the input transmit stream. For example, time diversity/space-time encoder 320 may decompose the input transmit stream into two copies. Transmit diversity/space-time encoder 320 may output a first of the two copies as a first encoded transmit stream and may further process a second of the two copies before outputting the second stream as a second encoded transmit stream. For example, the transmit diversity/space-time encoder 320 may process the second of the two duplicate transmit streams by delaying, conjugating, inverting, rotating, etc., or a combination thereof, the signal streams.

The transmitter system 300 beamforms each substream in the set of transmit diversity/space-time coded signal substreams. The first set of antennas includes antenna 340₀₀And 340₀₁And the second group includes an antenna 340₁₀And 340₁₁. Transmitter system 300 uses a first set of antennas 340₀₀And 340₀₁Beamforming a first transmit diversity/space-time coded signal sub-stream and using a second set of antennas 340₁₀And 340₁₁Beamforming is performed on the second transmit diversity/space-time coded signal sub-stream.

Transmit diversity/space-time encoder 320 couples the first encoded transmit stream to a first beamforming encoder 330₀. First beamforming encoder 330₀Including a signal splitter 410₀The splitter is used to split the first encoded transmit stream into two copies. First beamforming encoder 330₀Will come from the splitter 410₀Is coupled to a first antenna 340 associated with the transmit diversity group₀₀. First beamforming encoder 330₀Will come from the splitter 410₀Is coupled to the multiplier 420₀Multiplier 420₀For weighting the signal streams with complex weights received from the weight matrix generator 360. First beamforming encoder 330₀Coupling the weighted transmit streams to a second antenna 340 associated with a transmit diversity group₀₁。

Transmitter system 300 beamforms the second encoded transmit stream in a similar manner. Transmit diversity/space-time encoder 320 couples the second encoded transmit stream to a second beamforming encodingDevice 330₁. Second beamforming encoder 330₁Including a signal splitter 410₁The splitter is used to split the second encoded transmit stream into two copies. Second beamforming encoder 330₁Will come from the splitter 410₁Is coupled to a first antenna 340₁₀. Second beamforming encoder 330₁Will come from the splitter 410₁Is coupled to the multiplier 420₁Multiplier 420₁For weighting the signal streams with complex weights received from the weight matrix generator 360. Second beamforming encoder 330₁Coupling the weighted transmit streams to a second antenna 340₁₁。

The timing and synchronization module 350 is used to maintain synchronization with the system time used by the transmitter in generating the transmit stream. The timing and synchronization module 350 may also be used to monitor predetermined events or conditions of the transmitter 310. The timing and synchronization module 350 couples timing and event state information to the weight matrix generator 360.

The weight matrix generator 360 is represented as a 2 x 2 weight matrix generator because each transmit diversity group is beamformed on two different antennas. In a general case, the weight matrix generator 360 generates a 1 × 2 vector for each of two transmit diversity groups, thus forming a 2 × 2 weight matrix. But because in this example the beamforming encoder 330₀And 330₁Only one of the two signals transmitted to the antennas is weighted, so the weight matrix generator 360 need only generate one complex weight for each transmit diversity group.

The weight matrix generator 360 generates a 1 × 2 vector for each transmit diversity group, the first entry in the vector being predetermined to be the unit one. Thus, there is only one variable complex weight for each transmit diversity group. These weights may be considered to be normalized to a first weight.

The weight matrix generator 360 can use feedback from access terminals that receive the beamformed signals to modify or generate antenna weights. An access terminal may receive two beamformed signals and may generate one or more CQI values from the signals. The access terminal may generate a CQI value based in part on the channel observed at the receiver from the two beams.

Through g₀＝h₀+w₀·h₀' given the channel observed at the receiver of the access terminal in the first beam, where h_oIs from the first antenna 340₀₀Channel to receiver, h_o' is from a second antenna 340 of the same beam₀₁A channel to a receiver. Similarly, by g₁＝h₁+w₁·h₁' given the channel observed at the receiver of the access terminal in the second beam, where h₁Is from the second antenna 340₀₁Channel to receiver, h₁' is from the second antenna 340 of the second beam₁₁A channel to a receiver.

The receiver of the access terminal can estimate the channel based on the pilot signal transmitted by transmitter system 300. In one embodiment, the access terminal informs the transmitter system 300 of the channel g via the receiver 380 and the CQI processor 390₀And g₁Which is stronger. The weight matrix generator 360 may then adjust the weights of the weight vectors accordingly.

In one embodiment, the weight matrix generator 360 is used to vary the phase θ of the weights corresponding to the weaker channels according to a predetermined algorithm_i. For example, the weight matrix generator 360 may increment the phase by a predetermined increment value.

The access terminal may update the CQI value according to the modified beam. The updated CQI value informs the transmitter system 300 whether the corresponding channel gain is improved. If the channel gain improves, the weight matrix generator 360 may continue to change phase in the same manner until such changes no longer produce any improvement in the channel gain. If the change in phase reduces the channel gain, the weight matrix generator 360 may change the phase in the opposite manner, again, until no further improvement in channel gain is obtained.

After optimizing the phase, the weight matrix generator 360 may adjust and optimize the corresponding amplitude A_i. It should be noted that the phase and amplitude need not be continuous functions, but may be selected from a collection of discrete amplitudes and phases as shown in fig. 5.

The CQI value need not correspond to a single channel estimate but may also correspond to a value derived from a combination of channel estimates. The weight matrix generator 360 may be used to optimize the weights based on metrics derived from a combination of channel estimates or other parameters. For example, weight matrix generator 360 may be used to adjust weights to weight | g₀|²+|g₁|²And (4) maximizing.

The access terminal may be used to generate and feed back a CQI value, which may correspond to | g on the current transmission₀|²+|g₁|²The difference from the previous value. The weight matrix generator 360 updates the weights in an adaptive manner using this CQI value so that the difference is minimized.

Fig. 5 is an embodiment of a constellation diagram 500 showing a set of weights that a transmitter may select for a weight vector. Constellation diagram 500 includes 24 possible weights. Minimizing the number of possible weights in the constellation also minimizes the degrees of freedom and processing associated with changing the beamforming weights.

The 12 weights (e.g., weight 512a) are uniformly located on a circle having a first radius; the 12 weights (e.g., 510 and 521b) are uniformly located on a circle having a larger second radius. The phase of the weights on the first circle coincides exactly with the phase of the weights on the second circle. This structure enables the transmitter to change the magnitude of the weights without changing the phase of the weights. The transmitter may also change the vector of weights without changing the magnitude of the weights.

For example, the transmitter may determine that the magnitude of the weight currently corresponding to weight 512a should be increased. The transmitter may accomplish this by choosing to replace 512a with a weight 512 b. Similarly, the transmitter may introduce or change phase rotation by selecting constellation points that lie on the same circle.

Fig. 6 is a simplified functional block diagram of an embodiment of a receiver system 600 that generates and feeds back CQI values based on signals in multiple beams. Receiver system 600 may be, for example, part of the receiver system of fig. 2 or the access terminal of fig. 1.

Receiver system 600 is configured to generate a channel estimate for each beam of the plurality of beams based on pilot signals in one or more OFDM symbols carried in each beam. The receiver system 600 utilizes the channel estimates to determine one or more CQI values for transmission back to the transmitter over the wireless link.

Receiver system 600 includes an antenna 602 for receiving a beamformed signal (e.g., a transmit diversity/space-time coded beamformed signal from an access point in fig. 1 or a transmitter system in fig. 3 or 4). The antenna 602 couples the beamformed signals to a receiver 610, which is used to perform RF processing and frequency conversion. Receiver 610 may be used to process the received beamformed signals into baseband signals.

The receiver 610 couples the beamformed signals to a Discrete Fourier Transform (DFT) module 620 for processing. In the context of an OFDM symbol, DFT module 620 is operable to receive time-domain samples of the OFDM symbol and perform a fourier transform to produce corresponding frequency-domain information on each subcarrier in a substantially orthogonal set of subcarriers. For example, the DFT module 620 may perform fourier transforms using a fast fourier transform engine.

The subcarrier outputs from the DFT module 620 are coupled to a pilot extraction module 630. The transmitter system includes one or more pilot signals into predetermined locations of the OFDM symbol. Algorithms for locating pilot signals in OFDM symbols are known to receiver system 600. The pilot extraction module 630 extracts those subcarriers that correspond to the pilot signal based on knowledge of the pilot placement algorithm. In a simple pilot placement algorithm, the pilot signal occupies subcarriers that are evenly spaced in each OFDM symbol.

The pilot extraction module 630 couples the extracted pilot signal information to the channel estimator 640. Channel estimator 640 processes the pilot to determine a channel estimate.

DFT module 620, pilot extraction module 630 and channel estimator 640 operate to produce a channel estimate for each signal beam. In general, transmit diversity/space-time coding and beamforming performed at the transmitter system can ensure that each channel is uncorrelated with any other channel.

Channel estimator 640 couples the plurality of channel estimates to CQI generator 650. CQI generator 650 generates one or more CQI values based on the channel estimates. In one embodiment, CQI generator 650 is used to generate a CQI value representing each channel estimate. For example, the CQI value may correspond to a magnitude of the channel estimate. In another embodiment, CQI generator 650 may be operative to generate a CQI value based on a combination of a plurality of channel estimates. For example, CQI generator 650 may generate a CQI value that represents the sum of the squares of the magnitudes of several channel estimates. In another embodiment, CQI generator 650 may be used to indicate an improvement in signal quality or may indicate which beams experience a better channel. In other embodiments, CQI generator 650 may implement a combination of CQI generation techniques, or some other CQI generation technique.

CQI generator 650 couples CQI values to transmitter 660. The transmitter 660 formats the CQI value or values transmitted back to the transmitter system. The transmitter 660 may generate an overhead message with the CQI value and may process the overhead message into an RF signal. Transmitter 660 couples the RF signal with the CQI value to antenna 602 for transmission to a transmitter system.

Fig. 7 is a simplified flow diagram of a method 700 for providing transmit diversity using beamformed transmit diversity/space-time coding. Method 700 may be performed, for example, at an access point in fig. 1 or by a transmitter system shown in fig. 3 or fig. 4. For purposes of discussion, the method 700 is described as being performed by a transmitter system. The various processing operations shown in method 700 may be implemented in either time domain processing of a signal or frequency domain processing of a signal.

The methodology 700 begins at block 710, where the transmitter system generates a transmit stream at block 710. The transmit stream includes one or more pilot signals. For example, the transmitter system may generate a transmit stream of OFDM symbols that have been frequency converted to a desired RF operating frequency. At least a portion of the OFDM symbols include pilot signals.

The transmitter system proceeds to block 720 where the transmit streams are broken into G groups, where G represents an integer greater than 1. As an example, a transmitter system may be used to divide a transmit stream into G sub-streams using a splitter.

The transmitter system proceeds to block 730 where the G signal streams are time diversity/space-time coded. One or more of the G signal streams may be processed to introduce transmit diversity in the transmit stream. In one embodiment, the transmitter system may be used to process or modify the signal stream by delaying, conjugating, negating, rotating, or otherwise processing the signal stream. In addition, the transmitter system may implement a combination of multiple processing techniques in providing transmit diversity.

The transmitter system may divide (e.g., at block 740) each encoded transmit signal from the G encoded signal streams into a group of K signals. For example, a transmitter system may be used to divide each encoded transmit stream into K signals using a 1: K signal splitter. Therefore, after each of the G signal streams is divided, the transmitter system is to support N × K signals.

For clarity and convenience of description, method 700 is described as dividing each of the G signal sub-streams into a group of K signals. Method 700 is not limited to having the same number of antennas in each group. Thus, in an alternative embodiment, the transmitter system may divide each of the first subset of signal streams into groups of K1 signals each, and divide each of the second subset of signal streams into groups of K2 signals each, where K1 is not equal to K2. In another embodiment, the transmitter system may divide each of the G signal streams into a different number of streams for beamforming.

The transmitter system can process (e.g., at block 750) one or more received CQI values corresponding to at least one access terminal. These CQI values may indicate the quality of the received signal to the transmitter system. In particular, the transmitter system may compare the most recent CQI value to one or more previous CQI values to determine an adjustment to the beamforming weight vector.

For example, the transmitter system may determine that the most recent change to the weight vector improves signal quality at the receiver based on a comparison of the CQI values. The transmitter system may determine that the weight vector should be adjusted in the same direction as the previous adjustment, or may determine that some other aspect of the weight vector needs to be adjusted or its scale adjusted.

After the transmitter system divides each of the G signal streams into groups of substreams and processes the CQI values, the transmitter system proceeds to block 760 where weight vectors for each of the G groups are generated. In the embodiment shown in the flow chart, the transmitter system generates G weight vectors of length K. The transmitter system may generate a different weight vector for each of the G groups or may use the same weight vector for multiple groups. Each weight vector represents weights for beamforming the K signal streams in a group.

In one embodiment, the transmitter system is configured to first select a default weight vector from a fixed constellation of weight vectors. The transmitter system then modifies the weight vector based on the CQI value received from the access terminal. The transmitter system may change the weights in the weight vector continuously or in one or more discrete increments. In another embodiment, the transmitter system may be configured to select weights from a predetermined constellation of weights.

The transmitter system may be adapted to change the weights in a predetermined manner. For example, the transmitter system may be used to first optimize the phase of the weights and maintain a constant amplitude. The transmitter system may then optimize the magnitude of the weights after the phase has been optimized. The transmitter system may continue to alternately optimize phase and amplitude to continuously optimize the beamforming weights over varying channel conditions.

The transmitter system proceeds to block 770 where the K signal streams in each of the G groups are weighted according to the associated weight vector. The transmitter system proceeds to block 780 where the signal is transmitted on N × K antennas. Each group of K antennas transmits a beamformed representation from a corresponding stream of the group of G time diversity/space-time coded signal streams. The transmitter system may continue to perform method 700 for all transmitted information and may selectively activate or deactivate beamforming.

Fig. 8 is a simplified flow diagram of an embodiment of a method 800 for generating feedback information from beamformed transmit diversity/space-time coded signals. Method 800 can be performed, for example, by an access terminal in fig. 1 or a receiver system in fig. 6.

The methodology 800 begins at block 810, where the receiver system receives transmit diversity/space-time coded signals on a plurality of beams. The receiver system proceeds to block 820 where a pilot signal is extracted from the received signal.

In one embodiment, the pilot signal occupies a subset of the subcarriers of an OFDM symbol received by the receiver system. The pilot signal may be extracted from the OFDM symbol by transforming the time domain symbol samples into corresponding frequency domain subcarriers. The subcarriers corresponding to the pilot signal may be extracted from the complete set of frequency domain subcarriers.

The receiver system may compensate for transmit diversity/space-time coding as part of the pilot extraction process or as part of the channel estimation process. After extracting the pilot signal, the receiver system proceeds to block 830 where the channel for a particular beam corresponding to a particular transmit diversity/space-time code is estimated. The space-time code may be compensated for during channel estimation if the receiver system has not previously compensated for the transmit diversity/space-time code corresponding to a particular beam. Knowledge of the pilot enables the receiver system to estimate the channel corresponding to the beamformed and space-time coded signal stream.

After estimating the channel, the receiver system proceeds to block 840 where it is determined whether channel estimation has been performed for all space-time coded beams. Because the space-time coded beams are uncorrelated with each other, the receiver system can determine a different channel estimate for each space-time coded beam.

If the receiver system determines that the full channel estimate has not been determined, then the receiver system proceeds from decision block 840 back to block 820 to extract the pilot signal corresponding to another space-time coded beam. In the case where the transmitter system delays as part of the space-time coding process, the pilot extraction process may require an FFT to be performed on the delayed OFDM symbols to extract the pilots.

If at decision block 840 the receiver system determines that channel estimation has been performed for all beamformed space-time coded signals, the receiver system proceeds to block 850. At block 850, the receiver system generates one or more CQI values based on the channel estimates.

The receiver system may generate a CQI value that represents each channel estimate, represents a predetermined combination of channel estimates, represents a change in the predetermined combination of channel estimates, etc., or generates some other representation of the signal or channel quality. In one embodiment, the receiver system generates a CQI corresponding to the magnitude of each channel estimate. In another embodiment, the CQI generated by the receiver system is the sum of the squares of the magnitude of each channel estimate. In another embodiment, the CQI generated by the receiver system is used to rank the relative strengths of a predetermined number of beams.

After generating the one or more CQI values, the receiver system proceeds to block 860 where the CQI values are transmitted to the transmitter system. The receiver system may then return to block 810 to process additional received signals. For example, the receiver system may perform methodology 800 to update a CQI value per OFDM symbol, per frame of symbols, or some other increment.

Fig. 9 is a simplified functional block diagram of an embodiment of a transmitter system 900 for performing beamforming. Transmitter system 900 includes a processor 910 for transmitting for generating a transmit stream. The processor 910 for transmitting may include, for example, a signal source, modulator, frequency converter, and so on. In one embodiment, processor for transmitting 910 is configured to generate a transmit stream of OFDM symbols frequency converted to a transmit frequency.

A processor for transmitting 910 couples the transmit stream to a processor for transmit diversity/space-time coding 920. A processor 920 for transmit diversity/space-time coding is configured to generate G transmit diversity/space-time coded signal streams from the input transmit stream. A processor 920 for transmit diversity/space-time coding generates multiple signal streams from an input transmit stream and encodes each of the G signal streams to introduce transmit diversity.

For example, processor 920 for transmit diversity/space-time coding may include one or more elements for delaying, conjugating, inverting, rotating, or otherwise processing the signal streams.

A processor for transmit diversity/space-time coding 920 couples each of a plurality of coded transmit streams to a corresponding plurality of processors for beamforming 930₀-930_G. Transmitter system900 independently beamform each encoded transmit stream, and a processor (e.g., 930) for beamforming for each encoded transmit stream is implemented₀)。

Each processor for beamforming (e.g. 930)₀) Its corresponding encoded transmit stream is divided into K beamformed substreams. Processor (e.g., 930) for beamforming₀) The K beamformed substreams are weighted with weights from corresponding beamforming weight vectors provided by the processor 960 for generating the weight matrix.

Processor (e.g., 930) for beamforming₀) Coupling the K weighted beamformed substreams to multiple corresponding antennas (e.g., 940)₀₀-940_0K) Wherein the beamformed signals are transmitted to one or more receivers.

The processor 950 for providing timing and synchronization couples information related to events and timing synchronization to a processor 960 for generating a weight matrix. The receive antenna 970 is used to couple receive signals to the processor 980 for receive signals. The processor for receiving signals is configured to receive one or more feedback messages from each access terminal supported by the receiver system. The feedback message may include one or more CQI messages indicative of channel quality at the receiving access terminal.

Processor for receiving 980 processes the received signal to a baseband signal and couples the baseband signal to a processor 990 for processing Channel Quality Indication (CQI) values. A processor 990 for processing the CQI values operates on the baseband signal to extract one or more messages including the CQI values and extracts the CQI values from the messages. Processor 990 for processing CQI values can additionally maintain a correspondence between access terminals and CQI values, wherein CQI values corresponding to more than one access terminal are received at transmitter system 900.

Depending on the format of the CQI value, a processor 990 for processing the CQI value may also perform some processing on the received CQI value. For example, a processor for processing CQI values compares a most recent CQI value to one or more previously received CQI values to determine whether an adjustment to a weight vector results in an improvement in a signal at an access terminal. A processor 990 for processing the CQI values couples the CQI values, the processed CQI values, or a result of processing the CQI values to a processor 960 for generating a weight matrix.

A processor 960 for generating a weight matrix generates a processor 930 for beamforming based in part on received CQI values₀-930_GA weight vector for each processor in the set. In general, a processor 960 for generating a matrix of weights generates weights for each antenna and then a processor 930 for each beamforming₀-930_GIs a K-dimensional vector. The processor 960 for generating the weight matrix may be each of the processors 930 for beamforming₀-930_GDifferent weight vectors are generated or the same weight vector may be provided to two or more processors for beamforming.

Fig. 10 is a simplified functional block diagram of an embodiment of a receiver system 1000 for generating and feeding back CQI values based on signals in multiple beams. Receiver system 1000 can be, for example, a portion of the receiver system of fig. 2 or an access terminal of fig. 1. In the embodiment shown in fig. 10, receiver system 1000 is used to receive and process OFDM symbols. The particular modulation or multiplexing technique used to transmit the signal is not limiting of the invention.

Receiver system 1000 includes an antenna 1002 coupled to a processor for receiving 1010, processor for receiving 1010 for receiving a plurality of beams, each beam having a different space-time coded version of the signal. The receive processor 1010 is configured to process the received signal into a baseband signal and couple the baseband signal to a processor 1020 configured to convert the signal samples. The processor for transforming 1020 may be operative to transform the time-domain samples of the baseband signal into their frequency-domain counterparts. The processor for transforming 1020 may implement a DFT or FFT engine to perform the transform.

Processor for transforming 1020 couples frequency domain information to processor for extracting pilot signals 1030. The frequency domain information of the OFDM symbol corresponds to subcarriers that are substantially orthogonal to each other. A processor 1030 for extracting the pilot signal extracts the information on the subcarriers and the subcarriers corresponding to the pilot signal.

Processor for extracting pilot signals 1030 couples the pilot signals to a processor 1040 that estimates a channel. Since the pilot signal represents known transmission information, the channel can be estimated from the received signal. The processor 1040 for estimating the channel uses the known pilot signal to recover the channel estimate. Processor 1040 for estimating the channel may estimate the channel for each of the different space-time coded beams.

A processor 1030 for extracting pilot signals couples the channel estimates to a processor 1050 for generating CQI values. A processor 1050 for generating CQI values generates one or more CQI values based on the channel estimates. The CQI value indicates the channel quality or indicates a change in the channel quality.

A processor 1050 for generating CQI values couples the one or more CQI values to a processor 1060 for transmitting, the processor 1060 for transmitting for processing the CQI values into one or more signals for transmission back to the source of the beam. A processor for transmitting 1060 may be used to filter, amplify, and upconvert the CQI values or messages containing the CQI values to the RF band for transmission. A processor for transmitting 1060 couples the RF signal to the antenna 1002 where it is broadcast.

The methods and apparatus described herein enable a communication system to benefit from transmit diversity/space-time coding and beamforming simultaneously. The transmitter system is operable to independently beamform each of the set of transmit diversity/space-time coded signals. The transmitter system may vary the beamforming for each encoded signal stream from the set of transmit diversity/space-time encoded signals. The transmitter system may vary the beamforming for each signal stream based on the channel quality information provided by the beamformee. The transmitter system can vary the beamforming to optimize the signal quality at the receiver.

As used herein, the term "coupled" or "connected" means an indirect coupling as well as a direct coupling or connection. Where two or more blocks, modules, devices, or apparatus are coupled, there may be one or more intervening blocks between two coupled blocks.

The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose processor, a Digital Signal Processor (DSP), a Reduced Instruction Set Computer (RISC) processor, an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but, in the alternative, the general-purpose processor may be any processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The steps of a method, process, and algorithm described in one or more exemplary embodiments may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a computer. Such computer-readable media can include, for example, but is not limited to, RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to carry or store desired program code in the form of computer-accessible instructions or data structures. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, Digital Subscriber Line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk (disk) or disc, as used herein, includes Compact Disc (CD), laser disc, optical disc, Digital Versatile Disc (DVD), floppy disk and blu-ray disc where disks usually reproduce data electromagnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media. Thus, it should be appreciated that the computer-readable medium may be implemented with any suitable computer program product.

The previous description of the present disclosure is provided to enable any person skilled in the art to make or use the present disclosure. Various modifications to these embodiments will 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 of the disclosure. Thus, the present disclosure is not intended to be limited to the embodiments shown above but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (28)

1. A method for providing transmit diversity, the method comprising:

generating a plurality of space-time coded signals according to the transmission signal, wherein each space-time coded signal is respectively associated with a different space-time antenna group comprising a plurality of antennas;

receiving a channel quality indication from a first device, wherein the channel quality indication is based on a combination of a plurality of channel estimates;

generating at least one weight vector at the second device in accordance with the channel quality indication, wherein the generating at least one weight vector comprises: adjusting phases of weights in a weight vector without adjusting magnitudes of the weights until the phases are optimized; and

beamforming, at the second device, the plurality of space-time coded signals, wherein beamforming a particular space-time coded signal comprises: the space-time coded signal is divided into a plurality of replicated signal streams, the plurality of replicated signal streams are weighted respectively, and the weighted signal streams are provided to different antennas in an associated antenna group.

2. The method of claim 1, wherein generating the plurality of space-time coded signals comprises:

dividing the transmit signal stream into a plurality of replicated transmit signal streams;

delaying, rotating, conjugating, or a combination thereof, one of the plurality of replicated transmit signal streams.

3. The method of claim 1, wherein receiving the channel quality indication comprises:

a feedback message is received from a beamformed space-time coded signal receiver.

4. The method of claim 1, wherein receiving the channel quality indication comprises:

a signal representing a channel estimate is received from a beamformed space-time coded signal receiver.

5. The method of claim 1, wherein receiving the channel quality indication comprises:

a signal representing a combination of channel estimates is received from a beamformed space-time coded signal receiver.

6. The method of claim 1, wherein receiving the channel quality indication comprises:

a signal indicative of a change in signal quality at a beamformed space-time coded signal receiver is received.

7. The method of claim 1, wherein generating at least one weight vector comprises:

adjusting phases of weights in a weight vector according to the channel quality indication.

8. The method of claim 1, wherein generating at least one weight vector comprises:

adjusting magnitudes of weights in a weight vector according to the channel quality indication.

9. The method of claim 1, wherein generating at least one weight vector comprises:

selecting weights of a weight vector from a predetermined weight constellation, wherein the weight constellation comprises a first plurality of weights substantially uniformly located on a first circle having a first radius and a second plurality of weights substantially uniformly located on a second circle having a second radius, and wherein the second radius is larger than the first radius.

10. The method of claim 1, further comprising:

receiving a downlink interference estimate;

wherein generating at least one weight vector comprises:

generating at least one weight vector based on the channel quality indication and the downlink interference estimate.

11. A method for optimizing transmit diversity, the method comprising:

receiving a plurality of space-time coded signals in a plurality of signal beams from an access point, wherein each signal in the plurality of space-time coded signals is received in a different signal beam;

extracting at least one pilot signal from each signal beam;

determining a channel estimate for each signal beam based on the at least one pilot signal, wherein the channel estimate for a particular signal beam depends on channels from multiple antennas to a receiver;

determining whether channel estimates for all of the signal beams have been determined;

determining a channel quality indication from a combination of the channel estimates;

transmitting the channel quality indication as feedback information to a transmission source of the signal beam.

12. The method of claim 11, wherein determining the channel estimate comprises:

determining a channel estimate based on pilot signals in the signal beam.

13. The method of claim 11, wherein determining the channel quality indication comprises:

a channel quality value is determined for representing each channel estimate.

14. The method of claim 11, wherein determining the channel quality indication comprises:

the channel quality indication is determined from a combination of channel estimates.

15. An apparatus for providing transmit diversity, the apparatus comprising:

a transmitter to:

generating a transmit signal stream;

a transmit diversity encoder to:

-receiving said stream of transmitted signals and,

generating a plurality of transmit diversity/space-time coded transmit streams from the transmit signal stream, wherein the plurality of transmit diversity/space-time coded transmit streams is G, wherein each transmit diversity/space-time coded transmit stream is associated with a different antenna group comprising a plurality of antennas;

a weight matrix generator to:

receiving a channel quality indication from a first device, wherein the channel quality indication is based on a combination of a plurality of channel estimates;

generating, at the second device, at least one weight vector of a set of weight vectors in accordance with the channel quality indication, wherein generating at least one weight vector comprises: changing a phase of a weight without changing a magnitude of the weight until the phase is optimized; and

a plurality of beamforming encoders, each encoder of the plurality of beamforming encoders to:

receiving one of the plurality of transmit diversity/space-time coded transmit streams,

generating a plurality of weighted sub-streams for beamforming the plurality of transmit diversity/space-time coded transmit streams at the second device by providing the weighted sub-streams to different antennas of an associated group of antennas, respectively, according to weight vectors of the set of weight vectors, wherein the plurality of weighted sub-streams is K.

16. The apparatus of claim 15, further comprising:

a receiver to:

receiving a channel quality indication in at least one feedback message;

a processor to:

extracting the channel quality indication from the at least one feedback message;

transmitting the channel quality indication to the weight matrix generator.

17. The apparatus of claim 15, wherein the channel quality indication is indicative of a channel estimate.

18. The apparatus of claim 15, wherein the channel quality indication is indicative of a combination of channel estimates.

19. The apparatus of claim 15, wherein the channel quality indication is indicative of a change in channel estimation.

20. The apparatus of claim 15, wherein the weight matrix generator is configured to select weights from a predetermined set of weights.

21. The apparatus of claim 15, wherein the weight matrix generator is configured to vary a phase of at least one weight according to the channel quality indication.

22. The apparatus of claim 15, wherein the weight matrix generator is configured to vary a magnitude of at least one weight based on the channel quality indication.

23. An apparatus for optimizing transmit diversity, the apparatus comprising:

a receiver to:

receiving a plurality of space-time coded transmit signals in a plurality of beams, wherein each space-time coded transmit signal is transmitted in a different beam;

a pilot extraction module, coupled to the receiver, to:

extracting at least one pilot signal from each beam;

a channel estimation module, coupled to the pilot extraction module, to:

determining a channel estimate for each of the plurality of beams from the at least one pilot signal and determining whether channel estimates for all of the beams have been determined, wherein the channel estimate for a particular beam depends on the channels from the plurality of antennas to the receiver;

a channel quality indication generator to:

determining a channel quality indication from a combination of the channel estimates; and

a transmitter to:

generating a feedback message comprising the channel quality indication;

and sending the feedback message to the source end of the space-time coding sending signal.

24. The apparatus of claim 23, further comprising a transformation module to:

transforming time domain samples of the space-time coded transmit signal into a frequency domain representation;

wherein the pilot extraction module is configured to:

at least one pilot signal is extracted from the frequency domain representation.

25. The apparatus of claim 23, wherein the channel quality indication generator is to:

a different channel quality indication is generated from each channel estimate.

26. An apparatus for providing transmit diversity, the apparatus comprising:

means for generating a plurality of space-time coded signals from a transmit signal, wherein each space-time coded signal is associated with a different set of space-time antennas comprising a plurality of antennas;

means for receiving a channel quality indication from a first device, wherein the channel quality indication is based on a combination of a plurality of channel estimates;

means for generating at least one weight vector at a second device as a function of the channel quality indication, wherein the means for generating at least one weight vector comprises: means for adjusting phases of weights in a weight vector without adjusting magnitudes of the weights until the phases are optimized; and

means for beamforming the plurality of space-time coded signals at the second device, wherein means for beamforming a particular space-time coded signal comprises: the apparatus generally includes means for dividing the space-time coded signal into a plurality of replicated signal streams, means for weighting each of the plurality of replicated signal streams, and means for providing the weighted signal streams to different antennas of an associated antenna group.

27. An apparatus for optimizing transmit diversity, the apparatus comprising:

means for receiving a plurality of space-time coded signals in a plurality of signal beams from an access point, wherein each signal in the plurality of space-time coded signals is received in a different signal beam;

means for extracting at least one pilot signal from each signal beam;

means for determining a channel estimate for each signal beam based on the at least one pilot signal, wherein the channel estimate for a particular signal beam depends on channels from multiple antennas to a receiver;

means for determining whether channel estimates for all of the signal beams have been determined;

means for determining a channel quality indication from a combination of the channel estimates;

means for transmitting the channel quality indication as feedback information to a transmitting source of the signal beam.

28. A receiving system for optimizing transmit diversity, the system comprising:

a processor (1010) for receiving a plurality of space-time coded signals from an access point in a plurality of signal beams, wherein each signal in the plurality of space-time coded signals is received in a different signal beam;

a processor for extracting at least one pilot signal from each signal beam;

a processor (1040) for determining a channel estimate for each signal beam based on the at least one pilot signal, wherein the channel estimate for a particular signal beam depends on channels from multiple antennas to a receiver;

a processor for determining whether channel estimates for all of the signal beams have been determined;

a processor (1050) for determining a channel quality indication from the combination of channel estimates; and

a processor (1060) for transmitting the channel quality indication as feedback information to a transmission source of the signal beam.