Abstract: A “unified” MIMO system that supports multiple operating modes for efficient data transmission is described. Each operating mode is associated with different spatial processing at a transmitting entity. For example, four operating modes may be defined for (1) full-CSI or partial-CSI transmission and (2) with or without steering transmit diversity (STD). An appropriate operating mode may be selected for use based on various factors (e.g., availability of a good channel estimate). With steering transmit diversity, data is spatially spread and transmitted on multiple spatial channels, and a single rate may then be used for all spatial channels used for data transmission. A receiving entity may utilize a minimum mean square error (MMSE) technique for all operating modes. The receiving entity may derive a spatial filter matrix and perform receiver spatial processing in the same manner for all operating modes, albeit with different effective channel response matrices.

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 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: A method for estimating a feedback channel for a wireless repeater using frequency domain channel estimation estimates an error correction term using a most recent channel estimate and cancels the error correction term from a current block of the receive signal. Then, the feedback channel is estimated using frequency domain channel estimation and using a current block of the pilot signal and the corrected block of the receive signal. A channel estimate error term may also be estimated and subtracted directly from the channel estimate.

Abstract: A method for estimating a feedback channel for a wireless repeater uses frequency domain channel estimation and uses a signal indicative of the amplified signal as a pilot signal. The channel estimation method generates a time domain feedback channel estimate from the frequency domain channel estimation and scales the time domain feedback channel estimate using scaling factors. In one embodiment, the scaling factors are function of a tap index and the block size of the frequency domain channel estimation.

Abstract: Techniques for performing acquisition of packets are described. First detection values may be determined based on a first plurality of samples, e.g., by performing delay-multiply-integrate on the samples. Power values may be determined based on the first plurality of samples, e.g., by performing multiply-integrate on the samples. The first detection values may be averaged to obtain average detection values. The power values may also be averaged to obtain average power values. Whether a packet is presence may be determined based on the average detection values and the average power values. Second detection values may be determined based on a second plurality of samples. The start or the packet may be determined based on the first and second detection values. A third detection value may be determined based on a third plurality of samples. Frequency error of the packet may be estimated based on the first and third detection values.

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: 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: 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: Techniques for decomposing matrices using Jacobi rotation are described. Multiple iterations of Jacobi rotation are performed on a first matrix of complex values with multiple Jacobi rotation matrices of complex values to zero out the off-diagonal elements in the first matrix. For each iteration, a submatrix may be formed based on the first matrix and decomposed to obtain eigenvectors for the submatrix, and a Jacobi rotation matrix may be formed with the eigenvectors and used to update the first matrix. A second matrix of complex values, which contains orthogonal vectors, is derived based on the Jacobi rotation matrices. For eigenvalue decomposition, a third matrix of eigenvalues may be derived based on the Jacobi rotation matrices. For singular value decomposition, a fourth matrix with left singular vectors and a matrix of singular values may be derived based on the Jacobi rotation matrices.

Abstract: Techniques for performing sphere detection to recover data symbols sent in a MIMO transmission are described. In an aspect, sphere detection is performed for data symbols generated with at least two modulation schemes. In another aspect, sphere detection is performed for the data symbols in an order determined based on at least one attribute of the data symbols, which may be error probabilities, modulation schemes, and/or link margins for the data symbols. In yet another aspect, rates for multiple data streams detected with sphere detection are selected based on channel state information. Signal qualities of the data streams may be estimated based on the channel state information, e.g., (1) an upper triangular matrix used for sphere detection and/or (2) an assumption that interference from data streams already detected is canceled. The rates for the data streams may be selected based on the estimated signal qualities.

Abstract: Frequency-independent eigensteering in MISO and MIMO systems are described. For principal mode and multi-mode eigensteering, a correlation matrix is computed for a MIMO channel based on channel response matrices and decomposed to obtain NS frequency-independent steering vectors for NS spatial channels of the MIMO channel. ND data symbol streams are transmitted on ND best spatial channels using ND steering vectors, where ND=1 for principal mode eigensteering and ND>1 for multi-mode eigensteering. For main path eigensteering, a data symbol stream is transmitted on the best spatial channel for the main propagation path (e.g., with the highest energy) of the MIMO channel. For receiver eigensteering, a data symbol stream is steered toward a receive antenna based on a steering vector obtained for that receive antenna. For all eigensteering schemes, a matched filter is derived for each receive antenna based on the steering vector(s) and channel response vectors for the receive antenna.

Abstract: Techniques for transmitting data using a combination of transmit diversity schemes are described. These transmit diversity schemes include spatial spreading, continuous beamforming, cyclic delay diversity, space-time transmit diversity (STTD), space-frequency transmit diversity (SFTD), and orthogonal transmit diversity (OTD). A transmitting entity processes one or more (ND) data symbol streams based on a transmit diversity scheme (e.g., STTD, SFTD, or OTD) to generate multiple (NC) coded symbol streams. Each data symbol stream may be sent as a single coded symbol stream or as multiple (e.g., two) coded symbol streams using STTD, SFTD, or OTD. The transmitting entity may perform spatial spreading on the NC coded symbol streams with different matrices to generate multiple (NT) transmit symbol streams for transmission from NT antennas. Additionally or alternatively, the transmitting entity may perform continuous beamforming on the NT transmit symbol streams in either the time domain or the frequency domain.

Abstract: Techniques for performing acquisition of packets are described. First detection Values may be determined based on a first plurality of samples, e.g., by performing delay-multiply-integrate on the samples. Power values may be determined based on the first plurality of samples, e.g., by performing multiply-integrate on the samples. The first detection values may be averaged to obtain average detection values. The power values may also be averaged to obtain average power values. Whether a packet is present may be determined based on the average detection values and the average power values. Second detection values may be determined based on a second plurality of samples. The start of the packet may be determined based on the first and second detection values. A third detection value may be determined based on a third plurality of samples. Frequency error of the packet may be estimated based on the first and third detection values.

Abstract: A wireless repeater includes a channel estimation block to estimate a feedback channel between the antennas of the repeater using frequency domain channel estimation. The repeater includes a pilot signal blanking circuit to blank out a selected number of samples of the pilot signal to improve the accuracy of the channel estimation. In another embodiment, the repeater replaces T samples of the pilot signal with a cyclic prefix.

Abstract: A wireless repeater includes an echo canceller to cancel an estimated feedback amount from an input signal and a delay to delay the input signal. The delay may be selected to decorrelate a remote signal from a signal to be transmitted by the repeater.

Abstract: A wireless repeater having a receiving antenna for receiving an input signal and a transmitting antenna for transmitting an amplified signal includes first and second front-end circuits and a repeater baseband block coupled between the first and second front-end circuits. The repeater baseband block includes a channel estimation block, an echo canceller implementing time domain echo cancellation, a variable gain stage controlled by a gain control block implementing digital gain control, a first variable delay element introducing a first delay before or after the echo canceller, a second variable delay element introducing a second delay to the output signal. The delayed output signal is coupled to the channel estimation block as a reference signal for estimating the feedback channel, to the echo canceller as a reference signal for estimating the feedback signal, and to the gain control block for monitoring the stability of the repeater.

Abstract: Techniques for performing phase correction for wireless communication are described. Received pilot symbols and received data symbols may be obtained from an orthogonal frequency division multiplexing (OFDM) and/or multiple-input multiple-output (MIMO) transmission. First phase information is obtained based upon the received pilot symbols. Second phase information is obtained based upon the received data symbols. The phase of the received data symbols is corrected based upon the first and second phase information (directly and/or indirectly). For example, the phase of the received data symbols may be corrected based upon the first phase information, detection may be performed on the phase corrected data symbols to obtain estimated data symbols, the second phase information may be obtained based upon the estimated data symbols, and the phase of the estimated data symbols may be corrected based upon the second phase information. The phase correction may also be performed in other manners.

Abstract: Techniques to process data for transmission over a set of transmission channels selected from among all available transmission channels. In an aspect, the data processing includes coding data based on a common coding and modulation scheme to provide modulation symbols and pre-weighting the modulation symbols for each selected channel based on the channel's characteristics. The pre-weighting may be achieved by “inverting” the selected channels so that the received SNRs are approximately similar for all selected channels. With selective channel inversion, only channels having SNRs at or above a particular threshold are selected, “bad” channels are not used, and the total available transmit power is distributed across only “good” channels. Improved performance is achieved due to the combined benefits of using only the NS best channels and matching the received SNR of each selected channel to the SNR required by the selected coding and modulation scheme.

Abstract: In one aspect of a multiple-access OFDM-CDMA system, the data spreading is performed in the frequency domain by spreading each data stream with a respective spreading code selected from a set of available spreading codes. To support multiple access, system resources may be allocated and de-allocated to users (e.g., spreading codes may be assigned to users as needed, and transmit power may be allocated to users). Variable rate data for each user may be supported via a combination of spreading adjustment and transmit power scaling. Interference control techniques are also provided to improve system performance via power control of the downlink and/or uplink transmissions to achieve the desired level of performance while minimizing interference. A pilot may be transmitted by each transmitter unit to assist the receiver units perform acquisition, timing synchronization, carrier recovery, handoff, channel estimation, coherent data demodulation, and so on.