Abstract: Distortion correction from a distorted source image to a distortion corrected target image includes dividing the target image into a plurality of target tiles. The source image is divided into source tiles. Each source tile corresponds to a target tile according to a first mapping. The source tiles are processed to produce a source tile index until all the source tiles in the source image have been assigned a source tile index value in an ascending order. At least one y coordinate value of a first target tile is higher than a y coordinate value of a second target tile, wherein the first target tile corresponds to a source tile that appears earlier in the ascending order of the source tile index than a corresponding source tile of the second target tile. Distortion correction of the source image is performed by mapping each source tile to its corresponding target tile.

Abstract: In one embodiment, the present invention generates a single rotation angle that may be used to maximize diversity of a quasi-orthogonal space-time block code that encodes groups of four data symbols. Two rotation angles corresponding the first two data symbols in a group are set to zero, and two rotation angles corresponding to the second two data symbols in a group are set to a single initial value. A codeword distance matrix is determined for each possible combination of codewords and erroneously decoded codewords that may be generated using the initial rotation angle, and the minimum of the determinants of these matrices is selected. This process is repeated to generate a plurality of minimum determinants, and, for each iteration, a different single rotation angle corresponding to the second two data symbols is used. Then, a single rotation angle is selected that corresponds to the maximum of the minimum determinants.

Abstract: An exemplary fast Fourier transform (FFT) numerology for an orthogonal frequency division multiple access (OFDMA) downlink transmission system is described. The exemplary FFT numerology reduces the FFT sampling rate for a given transmission bandwidth, thereby increasing the battery life of a UE. The FFT numerology increases robustness against Doppler spread, phase noise, and frequency offset, enabling operation in channels with high delay spread, such as occurs in mountainous regions. The described numerology might provide the following without altering standard sub-frame duration: increased intercarrier spacing; reduced FFT sampling frequency across the transmission bandwidths; reduced FFT size across all transmission bandwidths; increased number of OFDM symbols per sub-frame; and/or increased cyclic prefix length choices.

Abstract: An exemplary fast Fourier transform (FFT) numerology for an orthogonal frequency division multiple access (OFDMA) downlink transmission system is described. The exemplary FFT numerology reduces the FFT sampling rate for a given transmission bandwidth, thereby increasing the battery life of a UE. The FFT numerology increases robustness against Doppler spread, phase noise, and frequency offset, enabling operation in channels with high delay spread, such as occurs in mountainous regions. The described numerology might provide the following without altering standard sub-frame duration: increased intercarrier spacing; reduced FFT sampling frequency across the transmission bandwidths; reduced FFT size across all transmission bandwidths; increased number of OFDM symbols per sub-frame; and/or increased cyclic prefix length choices.

Abstract: An exemplary fast Fourier transform (FFT) numerology for an orthogonal frequency division multiple access (OFDMA) downlink transmission system is described. The exemplary FFT numerology reduces the FFT sampling rate for a given transmission bandwidth, thereby increasing the battery life of a UE. The FFT numerology increases robustness against Doppler spread, phase noise, and frequency offset, enabling operation in channels with high delay spread, such as occurs in mountainous regions. The described numerology might provide the following without altering standard sub-frame duration: increased intercarrier spacing; reduced FFT sampling frequency across the transmission bandwidths; reduced FFT size across all transmission bandwidths; increased number of OFDM symbols per sub-frame; and/or increased cyclic prefix length choices.

Abstract: In one embodiment, a timing-offset estimator calculates a correlation value for each sample of an OFDM signal having a cyclic prefix for each OFDM symbol. The correlation value is provided to a tapped delay line that applies a separate weight to each of 2V correlation values, where V is the length of the cyclic prefix and the weights are based on a triangular weighting scheme that increases linearly from the first value, peaks at the Vth value, and decreases linearly to the 2Vth value. A stream of combined, squared correlation values is generated by combining and squaring the 2V weighted correlation values for each sample of the OFDM signal. For each cyclic prefix of the OFDM signal, a timing-offset estimate is determined based on a detected peak value in the stream of combined, squared correlation values. A timing-offset estimator with triangular weighting scheme may be implemented using recursive processing.

Abstract: In one embodiment, the present invention generates a single rotation angle that may be used to maximize diversity of a quasi-orthogonal space-time block code that encodes groups of four data symbols. Two rotation angles corresponding the first two data symbols in a group are set to zero, and two rotation angles corresponding to the second two data symbols in a group are set to a single initial value. A codeword distance matrix is determined for each possible combination of codewords and erroneously decoded codewords that may be generated using the initial rotation angle, and the minimum of the determinants of these matrices is selected. This process is repeated to generate a plurality of minimum determinants, and, for each iteration, a different single rotation angle corresponding to the second two data symbols is used. Then, a single rotation angle is selected that corresponds to the maximum of the minimum determinants.

Abstract: In one embodiment, a timing-offset estimator calculates a correlation value for each sample of an OFDM signal having a cyclic prefix for each OFDM symbol. The correlation value is provided to a tapped delay line that applies a separate weight to each of 2V correlation values, where V is the length of the cyclic prefix and the weights are based on a triangular weighting scheme that increases linearly from the first value, peaks at the Vth value, and decreases linearly to the 2Vth value. A stream of combined, squared correlation values is generated by combining and squaring the 2V weighted correlation values for each sample of the OFDM signal. For each cyclic prefix of the OFDM signal, a timing-offset estimate is determined based on a detected peak value in the stream of combined, squared correlation values. A timing-offset estimator with triangular weighting scheme may be implemented using recursive processing.

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.

Abstract: An exemplary fast Fourier transform (FFT) numerology for an orthogonal frequency division multiple access (OFDMA) downlink transmission system is described. The exemplary FFT numerology reduces the FFT sampling rate for a given transmission bandwidth, thereby increasing the battery life of a UE. The FFT numerology increases robustness against Doppler spread, phase noise, and frequency offset, enabling operation in channels with high delay spread, such as occurs in mountainous regions. The described numerology might provide the following without altering standard sub-frame duration: increased intercarrier spacing; reduced FFT sampling frequency across the transmission bandwidths; reduced FFT size across all transmission bandwidths; increased number of OFDM symbols per sub-frame; and/or increased cyclic prefix length choices.

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 transmits the long training sequence with an increased power level relative to a transmission of a payload by the active transmit antenna branch. The increased power level for the active transmit antenna branch compensates for the inactive transmit antenna branches being silent during the given time. Thus, the active transmit antenna branch provides approximately the same antenna power while transmitting the long training sequence as a total power of the plurality of transmit antenna branches during a transmission of the payload. The increased power level can be provided, for example, by a digital-to-analog converter associated with the active transmit antenna branch.

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 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 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 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.