Abstract: A method of phase correction at a wireless device includes: estimating a phase slope for an OFDM symbol in a data portion of a packet based on an elapsed time from the start of the packet; measuring a residual phase slope from tracking pilots for the OFDM symbol in the data portion of the packet; and adjusting a phase correction based upon the phase slope and the residual phase slope. Apparatus in a wireless device performs the method and machine-readable media carry instructions for carrying out the method.

Abstract: A method for identifying a reference point in time in a wireless communication system includes: receiving a first repeated sequence of symbols; receiving a second repeated sequence of symbols; performing an autocorrelation between the first and second sequences of symbols; and identifying as the reference point in time an autocorrelation null between the first and second repeated sequences of symbols. Apparatus for identifying a reference point in time in a wireless communication system includes: means for receiving a first repeated sequence of symbols; means for receiving a second repeated sequence of symbols; means for performing an autocorrelation between the first and second sequences of symbols; and means for identifying as the reference point in time an autocorrelation null between the first and second repeated sequences of symbols. Other aspects, features, and embodiments are also claimed and described.

Abstract: Techniques for extending transmission range in a WLAN are described. In an aspect, a receiving station determines the frequency error between a transmitting station and the receiving station based on one or more initial packet transmissions and corrects this frequency error for subsequent packet transmissions received from the transmitting station. The residual frequency error is small after correcting for the frequency error and allows the receiving station to perform coherent accumulation/integration over a longer time interval to detect for a packet transmission. The longer coherent accumulation interval improves detection performance, especially at low SNRs for extended transmission range. The techniques may be used whenever the receiving station knows the identity of the transmitting station, e.g., if the subsequent packet transmissions are scheduled. In another aspect, a preamble is generated with a longer spreading sequence and sent with each packet transmission.

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: 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: A power-efficient wireless device is equipped with multiple (N) antennas. Each antenna is associated with a transmitter unit and a receiver unit. The wireless device also has processing units used to perform various digital processing tasks. The transmitter units, receiver units, and processing units may be selectively enabled or disabled. In an idle state, the wireless device may enable only a subset (e.g., one) of the N receiver units and one or few processing units for signal detection and acquisition. For active communication, the wireless device may enable Ntx transmitter units for data transmission and/or Nrx receiver units for data reception, where 1?Ntx?N and 1?Nrx?N. The enabled processing units may also be clocked at a lower frequency whenever data is transmitted or received at a data rate lower than the highest data rate. The wireless device may go to sleep whenever possible to conserve power.

Abstract: Pilots suitable for use in MIMO systems and capable of supporting various functions are described. The various types of pilot include—a beacon pilot, a MIMO pilot, a steered reference or steered pilot, and a carrier pilot. The beacon pilot is transmitted from all transmit antennas and may be used for timing and frequency acquisition. The MIMO pilot is transmitted from all transmit antennas but is covered with different orthogonal codes assigned to the transmit antennas. The MIMO pilot may be used for channel estimation. The steered reference is transmitted on specific eigenmodes of a MIMO channel and is user terminal specific. The steered reference may be used for channel estimation. The carrier pilot may be transmitted on designated subbands/antennas and may be used for phase tracking of a carrier signal. Various pilot transmission schemes may be devised based on different combinations of these various types of pilot.

Abstract: A transmitting entity transmits a “base” pilot in each protocol data unit (PDU). A receiving entity is able to derive a sufficiently accurate channel response estimate of a MIMO channel with the base pilot under nominal (or most) channel conditions. The transmitting entity selectively transmits an additional pilot if and as needed, e.g., based on channel conditions and/or other factors. The additional pilot may be adaptively inserted in almost any symbol period in the PDU. The receiving entity is able to derive an improved channel response estimate with the additional pilot. The transmitting entity sends signaling to indicate that additional pilot is being sent. This signaling may be embedded within pilot symbols sent on a set of pilot subbands used for a carrier pilot that is transmitted across most of the PDU. The signaling indicates whether additional pilot is being sent and possibly other pertinent information.

Abstract: Certain aspects and embodiments provide for accurate measurement and estimation of imbalances between in-phase (I) and quadrature (Q) components of a complex baseband signal. The accuracy of I/Q phase imbalance estimates may be enhanced by conducting them on a transmitter and a receiver that are connected via a local, loopback connection and by removing cross-spectrum interference in transferred packets. Once these accurate I/Q phase imbalances are determined, they may be used to adjust a signal processed by the transmitter or the receiver to increase the performance and data throughput of communications using the signal.

Abstract: A method for identifying a reference point in time in a wireless communication system includes: receiving a first repeated sequence of symbols; receiving a second repeated sequence of symbols; performing an autocorrelation between the first and second sequences of symbols; and identifying as the reference point in time an autocorrelation null between the first and second repeated sequences of symbols. Apparatus for identifying a reference point in time in a wireless communication system includes: means for receiving a first repeated sequence of symbols; means for receiving a second repeated sequence of symbols; means for performing an autocorrelation between the first and second sequences of symbols; and means for identifying as the reference point in time an autocorrelation null between the first and second repeated sequences of symbols.

Abstract: Techniques for efficiently computing spatial filter matrices are described. The channel response matrices for a MIMO channel may be highly correlated if the channel is relatively static over a range of transmission spans. In this case, an initial spatial filter matrix may be derived based on one channel response matrix, and a spatial filter matrix for each transmission span may be computed based on the initial spatial filter matrix and a steering matrix used for that transmission span. The channel response matrices may be partially correlated if the MIMO channel is not static but does not change abruptly. In this case, a spatial filter matrix may be derived for one transmission span l and used to derive an initial spatial filter matrix for another transmission span m. A spatial filter matrix for transmission span m may be computed based on the initial spatial filter matrix, e.g., using an iterative procedure.

Abstract: Pilots suitable for use in MIMO systems and capable of supporting various functions are described. The various types of pilot include—a beacon pilot, a MIMO pilot, a steered reference or steered pilot, and a carrier pilot. The beacon pilot is transmitted from all transmit antennas and may be used for timing and frequency acquisition. The MIMO pilot is transmitted from all transmit antennas but is covered with different orthogonal codes assigned to the transmit antennas. The MIMO pilot may be used for channel estimation. The steered reference is transmitted on specific eigenmodes of a MIMO channel and is user terminal specific. The steered reference may be used for channel estimation. The carrier pilot may be transmitted on designated subbands/antennas and may be used for phase tracking of a carrier signal. Various pilot transmission schemes may be devised based on different combinations of these various types of pilot.

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: A receiving entity obtains received symbols for a data transmission having at least one data symbol stream sent with space-time transmit diversity (STTD). The receiving entity derives an overall channel response matrix in accordance with the STTD encoding scheme used for the data transmission, derives a spatial filter matrix based on the overall channel response matrix, and performs spatial matched filtering on a vector of received symbols for each 2-symbol interval to obtain a vector of detected symbols for the 2-symbol interval. The receiving entity may perform post-processing (e.g., conjugation) on the detected symbols if needed. Alternatively, the receiving entity derives a spatial filter matrix based on an effective channel response matrix, performs spatial matched filtering on the received symbols for each symbol period to obtain detected symbols for that symbol period, and combines multiple estimates obtained for each data symbol sent with STTD.

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 parse data into multiple (M) streams with selectable data rates are described. The modulation scheme and code rate for each stream are determined based on the data rate selected for that stream. The modulation schemes and code rates for all M streams are used to determine a parse cycle and the number of puncture cycles for each stream in the parse cycle. A sequence of puncture cycles is formed for the M streams such that the puncture cycle(s) for each stream are distributed as evenly as possible across the sequence. An encoder encodes traffic data in accordance with a base code (e.g., a rate 1/2 binary convolutional code) and generates code bits. A parser then parses the code bits into the M streams based on the sequence of puncture cycles, one puncture cycle at a time and in the order indicated by the sequence.

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.