Abstract: A multiple-access MIMO WLAN system that employs MIMO, OFDM, and TDD. The system (1) uses a channel structure with a number of configurable transport channels, (2) supports multiple rates and transmission modes, which are configurable based on channel conditions and user terminal capabilities, (3) employs a pilot structure with several types of pilot (e.g., beacon, MIMO, steered reference, and carrier pilots) for different functions, (4) implements rate, timing, and power control loops for proper system operation, and (5) employs random access for system access by the user terminals, fast acknowledgment, and quick resource assignments. Calibration may be performed to account for differences in the frequency responses of transmit/receive chains at the access point and user terminals. The spatial processing may then be simplified by taking advantage of the reciprocal nature of the downlink and uplink and the calibration.

Abstract: A multiple-access MIMO WLAN system that employs MIMO, OFDM, and TDD. The system (1) uses a channel structure with a number of configurable transport channels, (2) supports multiple rates and transmission modes, which are configurable based on channel conditions and user terminal capabilities, (3) employs a pilot structure with several types of pilot (e.g., beacon, MIMO, steered reference, and carrier pilots) for different functions, (4) implements rate, timing, and power control loops for proper system operation, and (5) employs random access for system access by the user terminals, fast acknowledgment, and quick resource assignments. Calibration may be performed to account for differences in the frequency responses of transmit/receive chains at the access point and user terminals. The spatial processing may then be simplified by taking advantage of the reciprocal nature of the downlink and uplink and the calibration.

Abstract: A transmitting entity uses different steering vectors for different subbands to achieve steering diversity. Each steering vector defines or forms a beam for an associated subband. Any steering vector may be used for steering diversity. The steering vectors may be defined such that the beams vary in a continuous instead of abrupt manner across the subbands. This may be achieved by applying continuously changing phase shifts across the subbands for each transmit antenna. As an example, the phase shifts may change in a linear manner across the subbands for each transmit antenna, and each antenna may be associated with a different phase slope. The application of linearly changing phase shifts to modulation symbols in the frequency domain may be achieved by either delaying or circularly shifting the corresponding time-domain samples.

Abstract: A MIMO system supports multiple spatial multiplexing modes for improved performance and greater flexibility. These modes may include (1) a single-user steered mode that transmits multiple data streams on orthogonal spatial channels to a single receiver, (2) a single-user non-steered mode that transmits multiple data streams from multiple antennas to a single receiver without spatial processing at a transmitter, (3) a multi-user steered mode that transmits multiple data streams simultaneously to multiple receivers with spatial processing at a transmitter, and (4) a multi-user non-steered mode that transmits multiple data streams from multiple antennas (co-located or non co-located) without spatial processing at the transmitter(s) to receiver(s) having multiple antennas. For each set of user terminal(s) selected for data transmission on the downlink and/or uplink, a spatial multiplexing mode is selected for the user terminal set from among the multiple spatial multiplexing modes supported by the system.

Abstract: A MIMO system supports multiple spatial multiplexing modes for improved performance and greater flexibility. These modes may include (1) a single-user steered mode that transmits multiple data streams on orthogonal spatial channels to a single receiver, (2) a single-user non-steered mode that transmits multiple data streams from multiple antennas to a single receiver without spatial processing at a transmitter, (3) a multi-user steered mode that transmits multiple data streams simultaneously to multiple receivers with spatial processing at a transmitter, and (4) a multi-user non-steered mode that transmits multiple data streams from multiple antennas (co-located or non co-located) without spatial processing at the transmitter(s) to receiver(s) having multiple antennas. For each set of user terminal(s) selected for data transmission on the downlink and/or uplink, a spatial multiplexing mode is selected for the user terminal set from among the multiple spatial multiplexing modes supported by the system.

Abstract: Techniques for processing a data transmission at the transmitter and receiver. In an aspect, a time-domain implementation is provided which uses frequency-domain singular value decomposition and “water-pouring” results to derive time-domain pulse-shaping and beam-steering solutions at the transmitter and receiver. The singular value decomposition is performed at the transmitter to determine eigen-modes (i.e., spatial subchannels) of the MIMO channel and to derive a first set of steering vectors used to “precondition” modulation symbols. The singular value decomposition is also performed at the receiver to derive a second set of steering vectors used to precondition the received signals such that orthogonal symbol streams are recovered at the receiver, which can simplify the receiver processing. Water-pouring analysis is used to more optimally allocate the total available transmit power to the eigen-modes, which then determines the data rate and the coding and modulation scheme to be used for each eigen-mode.

Abstract: Disclosed herein are methods and apparatus for enhancing the estimation of channel response in a wireless communication system.

Abstract: Techniques for transmitting data from a transmitter unit to a receiver unit in a multiple-input multiple-output (MIMO) communication system. In one method, at the receiver unit, a number of signals are received via a number of receive antennas, with the received signal from each receive antenna comprising a combination of one or more signals transmitted from the transmitter unit. The received signals are processed to derive channel state information (CSI) indicative of characteristics of a number of transmission channels used for data transmission. The CSI is transmitted back to the transmitter unit. At the transmitter unit, the CSI from the receiver unit is received and data for transmission to the receiver unit is processed based on the received CSI.

Abstract: When insufficient traffic is present in the network to maintain synchronization in this manner, other methods must be used. One approach involves making direct measurements of the timing between base stations. This is accomplished in one of two ways. The base may interrupt its transmissions on all sectors for a short interval during which it determines the time of arrival of signals from other base stations. Given knowledge of the other base station locations, time errors relative to all other base stations may be derived. Alternatively, the base may send a short signal at high power in the mobile transmit band. This time-of-arrival of this signal is measured by the surrounding base stations and the time errors between pairs of base stations are computed. In some cases, a base station may be isolated sufficiently from all other base stations in the network such that direct base-to-base measurement is not viable.

Abstract: A matrix {circumflex over (V)} of eigenvectors is derived using an iterative procedure. For the procedure, an eigenmode matrix Vi is first initialized, e.g., to an identity matrix. The eigenmode matrix Vi is then updated based on a channel response matrix ? for a MIMO channel to obtain an updated eigenmode matrix Vi+1. The eigenmode matrix may be updated for a fixed or variable number of iterations. The columns of the updated eigenmode matrix may be orthogonalized periodically to improve performance and ensure stability of the iterative procedure. In one embodiment, after completion of all iterations, the updated eigenmode matrix for the last iteration is provided as the matrix {circumflex over (V)}.

Abstract: For data transmission with spatial spreading, a transmitting entity (1) encodes and modulates each data packet to obtain a corresponding data symbol block, (2) multiplexes data symbol blocks onto NS data symbol streams for transmission on NS transmission channels of a MIMO channel, (3) spatially spreads the NS data symbol streams with steering matrices, and (4) spatially processes NS spread symbol streams for full-CSI transmission on NS eigenmodes or partial-CSI transmission on NS spatial channels of the MIMO channel. A receiving entity (1) obtains NR received symbol streams via NR receive antennas, (2) performs receiver spatial processing for full-CSI or partial-CSI transmission to obtain NS detected symbol streams, (3) spatially despreads the NS detected symbol streams with the same steering matrices used by the transmitting entity to obtain NS recovered symbol streams, and (4) demodulates and decodes each recovered symbol block to obtain a corresponding decoded data packet.

Abstract: A user terminal supports multiple spatial multiplexing (SM) modes such as a steered mode and a non-steered mode. For data transmission, multiple data streams are coded and modulated in accordance with their selected rates to obtain multiple data symbol streams. These streams are then spatially processed in accordance with a selected SM mode (e.g., with a matrix of steering vectors for the steered mode and with the identity matrix for the non-steered mode) to obtain multiple transmit symbol streams for transmission from multiple antennas. For data reception, multiple received symbol streams are spatially processed in accordance with the selected SM mode (e.g., with a matrix of eigenvectors for the steered mode and with a spatial filter matrix for the non-steered mode) to obtain multiple recovered data symbol streams. These streams are demodulated and decoded in accordance with their selected rates to obtain multiple decoded data streams.

Abstract: An access point in a multi-antenna system broadcasts data using spatial spreading to randomize an “effective” channel observed by each user terminal for each block of data symbols broadcast by the access point. At the access point, data is coded, interleaved, and modulated to obtain ND data symbol blocks to be broadcast in NM transmission spans, where ND?1 and NM>1. The ND data symbol blocks are partitioned into NM data symbol subblocks, one subblock for each transmission span. A steering matrix is selected (e.g., in a deterministic or pseudo-random manner from among a set of L steering matrices) for each subblock. Each data symbol subblock is spatially processed with the steering matrix selected for that subblock to obtain transmit symbols, which are further processed and broadcast via NT transmit antennas and in one transmission span to user terminals within a broadcast coverage area.

Abstract: An uplink channel response matrix is obtained for each terminal and decomposed to obtain a steering vector used by the terminal to transmit on the uplink. An “effective” uplink channel response vector is formed for each terminal based on its steering vector and its channel response matrix. Multiple sets of terminals are evaluated based on their effective channel response vectors to determine the best set (e.g., with highest overall throughput) for uplink transmission. Each selected terminal performs spatial processing on its data symbol stream with its steering vector and transmits its spatially processed data symbol stream to an access point. The multiple selected terminals simultaneously transmit their data symbol streams via their respective MIMO channels to the access point. The access point performs receiver spatial processing on its received symbol streams in accordance with a receiver spatial processing technique to recover the data symbol streams transmitted by the selected terminals.

Abstract: Techniques for transmitting data using channel information for a subset of all subcarriers used for data transmission are described. A transmitter station receives channel information for at least one subcarrier that is a subset of multiple subcarriers used for data transmission. The channel information may include at least one transmit steering matrix, at least one set of eigenvectors, at least one channel response matrix, at least one channel covariance matrix, an unsteered pilot, or a steered pilot for the at least one subcarrier. The transmitter station obtains at least one transmit steering matrix for the at least one subcarrier from the channel information and determines a transmit steering matrix for each of the multiple subcarriers. The transmitter station performs transmit steering or beam-steering for each of the multiple subcarriers with the transmit steering matrix for that subcarrier.

Abstract: Techniques to schedule downlink data transmission to a number of terminals in a wireless communication system. In one method, one or more sets of terminals are formed for possible data transmission, with each set including a unique combination of one or more terminals and corresponding to a hypothesis to be evaluated. One or more sub-hypotheses may further be formed for each hypothesis, with each sub-hypothesis corresponding to specific assignments of a number of transmit antennas to the one or more terminals in the hypothesis. The performance of each sub-hypothesis is then evaluated, and one of the evaluated sub-hypotheses is selected based on their performance. The terminal(s) in the selected sub-hypothesis are then scheduled for data transmission, and data is thereafter coded, modulated, and transmitted to each scheduled terminal from one or more transmit antennas assigned to the terminal.

Abstract: The downlink and uplink are calibrated to account for differences in the responses of transmit and receive chains at an access point and a user terminal. For initial calibration, the access point and user terminal transmit MIMO pilots on the downlink and uplink, which are used to derive channel estimates including the responses of the applicable transmit/receive chains. Correction matrices {circumflex over (K)}ap and {circumflex over (K)}ut are derived based on these channel estimates and thereafter used by the access point and user terminal, respectively. For follow-on calibration, one entity transmits a MIMO pilot and a steered reference. The other entity derives a first transmit matrix based on the steered reference and a second transmit matrix based on the MIMO pilot and calibration error matrices Qap and Qut, which contain estimates of the errors in {circumflex over (K)}ap and {circumflex over (K)}ut, respectively.

Abstract: Techniques to perform beam-steering and beam-forming to transmit data on a single eigenmode in a wideband multiple-input channel. In one method, a steering vector is obtained for each of a number of subbands. Depending on how the steering vectors are defined, beam-steering or beam-forming can be achieved for each subband. The total transmit power is allocated to the subbands based on a particular power allocation scheme (e.g., full channel inversion, selective channel inversion, water-filling, or uniform). A scaling value is then obtained for each subband based on its allocated transmit power. Data to be transmitted is coded and modulated to provide modulation symbols. The modulation symbols to be transmitted on each subband are scaled with the subband's scaling value and further preconditioned with the subband's steering vector. A stream of preconditioned symbols is then formed for each transmit antenna.

Abstract: For data transmission with spatial spreading, a transmitting entity (1) encodes and modulates each data packet to obtain a corresponding data symbol block, (2) multiplexes data symbol blocks onto NS data symbol streams for transmission on NS transmission channels of a MIMO channel, (3) spatially spreads the NS data symbol streams with steering matrices, and (4) spatially processes NS spread symbol streams for full-CSI transmission on NS eigenmodes or partial-CSI transmission on NS spatial channels of the MIMO channel. A receiving entity (1) obtains NR received symbol streams via NR receive antennas, (2) performs receiver spatial processing for full-CSI or partial-CSI transmission to obtain NS detected symbol streams, (3) spatially despreads the NS detected symbol streams with the same steering matrices used by the transmitting entity to obtain NS recovered symbol streams, and (4) demodulates and decodes each recovered symbol block to obtain a corresponding decoded data packet.

Abstract: Techniques to schedule uplink data transmission for a number of terminals in a wireless communication system. In one method, a number of sets of terminals are formed for possible data transmission, with each set including a unique combination of terminals and corresponds to a hypothesis to be evaluated. The performance of each hypothesis is evaluated (e.g., based on channel response estimates for each terminal) and one of the evaluated hypotheses is selected based on the performance. The terminals in the selected hypothesis are scheduled for data transmission. A successive cancellation receiver processing scheme may be used to process the signals transmitted by the scheduled terminals. In this case, one or more orderings of the terminals in each set may be formed, with each terminal ordering corresponding to a sub-hypothesis to be evaluated. The performance of each sub-hypothesis is then evaluated and one of the sub-hypotheses is selected.