Abstract: Methods and apparatus are provided for per-antenna training in a multiple antenna communication system having a plurality of transmit antenna branches. A long training sequence is transmitted on each of the transmit antenna branches such that only one of the transmit antenna branches is active at a given time. The active transmit antenna branch is configured in a transmit mode during the given time and one or more of the inactive transmit antenna branches are configured in a receive mode during the given time. The transmit and receive modes are configured, for example, by applying a control signal to one or more switches.

Abstract: Methods and apparatus are provided for improved short preamble formats in a multiple antenna communication system having N antennas. A short preamble format having a legacy portion and a high throughput portion is transmitted (or received) on each of the N transmit antennas, wherein the legacy portion comprises a legacy long training field and the high throughput portion comprises N-1 high throughput long training fields. The legacy long training field and the N-1 high throughput long training fields can be transmitted in N time slots using an N×N orthogonal matrix, such as a Walsh matrix or a Fourier matrix. The N time slots can optionally comprise a single symbol. Backwards compatibility is optionally maintained by including a legacy short training field and a legacy signal field in the legacy portion of the short preamble.

Abstract: Methods and apparatus are provided for improved long preamble formats in a multiple antenna communication system having N antennas. According to one aspect of the invention, a preamble having a legacy portion and a high throughput portion is transmitted (or received) on each of the N transmit antennas, wherein the legacy portion comprises a legacy long training field and the high throughput portion comprises at least N high throughput long training fields, wherein the N high throughput long training fields are transmitted in N time slots using an N×N orthogonal matrix. The orthogonal matrix can be, for example, one or more of a Walsh matrix and a Fourier matrix. The N time slots can optionally comprise a single symbol.

Abstract: Methods and apparatus are provided for reducing power fluctuations during preamble training in a multiple antenna communication system using cyclic delays. A preamble having a legacy portion and a high throughput portion is transmitted (or received) on each of N antennas, wherein at least a portion of the preamble on a first of the N antennas is delayed relative to at least the portion of the preamble on a second of the N antennas, wherein the delay is non-orthogonal amount to introduce variation across the preambles transmitted on the N transmit antennas. The legacy portion may be, for example, an 802.11 a/g preamble.

Abstract: A method for processing a received encoded data unit comprises: decoding the received encoded data unit; determining whether the encoded data unit has been correctly received; prior to completing the determination of whether the encoded data unit has been correctly received, initiating the transmission of an acknowledgment message; and modifying the transmission of the acknowledgment message if it is determined that the data unit has not been correctly received. In another embodiment, a station for a communications network comprises: a decoder adapted to decode a received encoded data unit; a check processor adapted to determine whether the encoded data unit has been correctly received; and a transmitter adapted to initiate the transmission of an acknowledgment message prior to the check processor completing the determination whether the encoded data unit has been correctly received.

Abstract: Methods and apparatus are provided for improved efficiency in an extended multiple antenna communication system. A multiplier is employed on the number of points in the FFT that is greater than the multiplier on the frequency (bandwidth) of the legacy 802.11 a/g system. In one exemplary implementation, a 256 point FFT is employed in 40 MHz (with a 4N multiplier on the number of possible tones and a 2N multiplier on the frequency). While the efficiency for the OFDM symbol is improved, additional overhead is required in the preamble training (the length of the preamble is proportional to the number of tones in the FFT). Thus, a number of preamble constructs are provided that couple the improved efficiency with shorter preambles. In addition, an improved tone design provides additional efficiency gains.

Abstract: Methods and apparatus are provided for varying the number of pilot tones in a multiple antenna communication system. Data is transmitted in a multiple antenna communication system by selecting a number of pilot tones to be employed to transmit the data; and transmitting an indication of the selected number of pilot tones in a preamble of a packet containing the data. Data is received in a multiple antenna communication system by receiving a preamble having an indication of a number of pilot tones embedded in the data; and processing the received data based on the indicated number of pilot tones. The indication of the selected number of pilot tones can be transmitted, for example, in a SIGNAL field of an exemplary IEEE 802.11 preamble. The number of pilot tones can be selected, for example, based on one or more of (i) a delay spread of a channel; (ii) the SNR at the receiver; or (iii) a number of antennas at a receiver.

Abstract: Methods and apparatus are provided for increasing data throughput in a multiple antenna communication system using additional subcarriers. The multiple antenna communication system includes at least one legacy system employing an N1 point fast Fourier transform (FFT) within a bandwidth, BW1. Data is transmitted using an N2 point inverse FFT within the bandwidth, BW1, wherein N2 is greater than N1; and subcarriers associated with the N2 point inverse FFT are employed to transmit the data. Data can also be transmitted using an N2 point inverse FFT within a bandwidth, BW2, wherein N2 is greater than N1 and the bandwidth, BW2, is greater than the bandwidth, BW1; and subcarriers associated with the N2 point inverse FFT are employed to transmit the data, wherein the employed subcarriers includes one or more additional subcarriers at outer edges of the bandwidth, BW1, relative to the legacy system and one or more additional subcarriers near DC relative to the legacy system.

Abstract: Methods and apparatus are disclosed for processing received data in a multiple input multiple output (MIMO) communication system. A multiple antenna receiver can distinguish a MIMO transmission from other transmissions based on the detection of a predefined symbol following a legacy portion of a preamble. A preamble comprises a legacy portion and an extended portion. The legacy portion is comprised of a first long preamble followed by a first signal field and may be processed by both multiple antenna receivers and legacy receivers. The extended portion comprises the predefined symbol following the first signal field from the legacy portion. If the predefined symbol is a second long preamble, a MIMO transmission is detected by performing a correlation on the preamble to detect the second long preamble. If the predefined symbol is a second long signal field, a MIMO transmission is detected by performing a cyclic redundancy check to detect the second long signal field.

Abstract: Methods and apparatus are provided for communicating data in a multiple antenna communication system having N transmit antennas. According to one aspect of the invention, a header format includes a legacy preamble having at least one legacy long training field and an extended portion having at least N additional long training fields on each of the N transmit antennas. The N additional long training fields may be tone interleaved across the N transmit antennas and are used for MIMO channel estimation. The extended portion may include a short training field for power estimation. The short training field may be tone interleaved across the N transmit antennas and have an extended duration to support beam steering.

Abstract: A maximum a posteriori (MAP) processor employs a block processing technique for the MAP algorithm to provide a parallel architecture that allows for multiple word memory read/write processing and voltage scaling of a given circuit implementation. The block processing technique forms a merged trellis with states having modified branch inputs to provide the parallel structure. When block processing occurs, the trellis may be modified to show transitions from the oldest state at time k−N to the present state at time k. For the merged trellis, the number of states remains the same, but each state receives 2N input transitions instead of the two input transitions. Branch metrics associated with the transitions in the merged trellis are cumulative, and are employed for the update process of forward and backward probabilities by the MAP algorithm.