Abstract: A decoding scheme for determining the information within a coded transmission includes a spherical decoder candidate search that reduces the number of candidate symbol combinations from a much larger number of possibly transmitted combinations. In one example, the spherical decoder uses an upper triangular matrix representation of the channel matrix as part of a recursive, cumulative cost function that provides the results of the candidate search. The candidate search includes considering symbols in a hierarchy or tree structure that represents the possibly transmitted combinations. The cost function incrementally accumulates a cost of a possible combination as the search progresses through the hierarchy. As soon as a symbol is determined to not be a valid candidate, all possible combinations including that symbol are discarded without considering them, directly.

Abstract: Systems and methods for packet detection for frequency hopping networks. Multiple receiver chains are set to different frequencies to check for packets at the different frequencies, at least until receipt of a preamble sequence in a packet is received. After detection of a packet at least some of the receiver chains are used to process received signals according to a frequency hopping pattern.

Abstract: Frame synchronization methods and systems suited for packet communications systems, and particularly time frequency hopping packet communication systems, are disclosed. Frame synchronization is performed by performing a first correlation on information of received symbols and performing a second correlation on results of the first correlation. In systems with repeating synchronization information modulated by a cover sequence, the results of the second correlation may be used to determine symbol numbering of symbols in a packet.

Abstract: Pairs of parallel Viterbi decoders use windowed block data for decoding data at rates above 320 Mbps. Memory banks of the deinterleavers feeding the decoders operate such that some are receiving data while others are sending data to the decoders. Parallel input streams to every pair of decoders overlap for several traceback lengths of the decoder causing data input to a first decoder at the end of an input stream to be the same as the data input to a second decoder of the same pair at the beginning of an input stream. Then, the first decoder is able to post-synchronize its path metric with the second decoder and the second decoder is able to pre-synchronize its path metric with the first. Either, the deinterleaver data length is an integer multiple of the traceback length or the data input to only the first block of the first interleaver is padded.

Abstract: Transmission systems and methods for reducing interference by wideband communication systems with narrowband communications systems are disclosed. In some embodiments an ultrawideband system employing orthogonal frequency division multiplexing (OFDM) with a null post-fix nulls symbols for sub-carriers at potentially interfering frequencies prior to transformation to the time domain and filters a time domain representation using a notch filter to further reduce spectral components at the potentially interfering frequencies. In further embodiments pre-emphasis is applied to a frequency domain representation of symbols to reduce ripples introduced by the notch filter.

Abstract: A method and system for estimating DC offset and removing the excess DC offset from samples used by an overlap-and-add operation at the receiver of OFDM symbols in UWB communication. The DC offset for each sample within the overlap-and-add interval may be estimated using a sliding window, of the size required for an FFT, operation over past samples. The DC offset may be estimated for a sample within the overlap-and-add interval and updated for the succeeding samples. A size of the overlap-and-add interval may be fixed or may be allowed to vary according to switching characteristics of an analog RF stage preceding the overlap-and-add operation.

Abstract: Methods and systems for packet preamble sequences are provided. The preamble sequences are produce by multiplying preestablished base sequences by cover sequences. The cover sequences are chosen for high-performance in multi-band OFDM systems with modes that include two-band hopping.

Abstract: A method and system for detecting the presence of narrowband transmitters utilizing frequencies also utilized by wider band communication systems. In some embodiments an ultrawideband transceiver detects signals at specific frequencies within a spectrum of frequencies, and analyzes the signals to determine if the signals indicate transmissions by a narrowband transmitter in a narrowband communication system. In further embodiments transmission circuitry reduces signal components at frequencies occupied by the narrowband transmitters.

Abstract: A modulation and coding scheme for a communication system is based on use of nonsystematic repeat-accumulate codes for encoding channel information for transmission, and for employing a combined detection and decoding arrangement to decode the coded channel information. The nonsystematic repeat-accumulate codes may be generated by an encoder at a transmitter and decoded by a composite detector/decoder arrangement at a receiver.

Abstract: A receiver in a wireless communication system scales received information to allow for improved decoder performance after bit reduction of the information. Mean values of the received information may be used to scale the information, with a plurality of mean values determined, each in a different way. Depending on types of spreading applied to the information by a transmitter, as indicated by a rate signal, different ones of the mean values are used for scaling. Preferably the mean values are determined using channel compensated information.

Abstract: Transmission systems and methods for reducing interference by wideband communication systems with narrowband communications systems are disclosed. In some embodiments an ultrawideband system employing orthogonal frequency division multiplexing (OFDM) with a null post-fix nulls symbols for sub-carriers at potentially interfering frequencies prior to transformation to the time domain and filters a time domain representation using a notch filter to further reduce spectral components at the potentially interfering frequencies. In further embodiments pre-emphasis is applied to a frequency domain representation of symbols to reduce ripples introduced by the notch filter.

Abstract: A receiver including a channel estimation function in which an initial channel estimate is filtered to increase receiver operation, particularly when the receiver may only have a limited number of channel estimation symbols with which to form the channel estimate. In some embodiments the filtering is performed by transforming the initial channel estimate to the time domain, zeroing some of the samples to filter the time domain channel estimate, and transforming the filtered time domain channel estimate to the frequency domain for use in channel compensation.

Abstract: Techniques and systems for design and use of generalized LDPC codes. A generalized LDPC code comprises a set of codewords producing valid results when submitted to a validator comprising a set of variable nodes and a set of check nodes, with outputs of the variable nodes being connected to inputs of the check nodes by interleaver edges. Each check node and variable node is in the form of a code, with the output of a node being valid if its inputs form a valid codeword. An extrinsic information transfer function (EXIT) chart is used to form a check node curve and a variable node curve is matched to the check node curve. The variable nodes are then constructed so as to provide the information transfer properties indicated by the variable node curve.

Abstract: Techniques for transmitting and receiving signals using a linear propagation channel, and the detection and decoding of the signals, are described. The symbols are decoded by computing the likelihood of each bit in a block of data in light of all blocks of received complex data and the constraints imposed by the channel code. Extrinsic information and a priori information are exchanged in an iterative fashion until desired performance is achieved. Extrinsic probability values are computed by searching through hypotheses in the constellation of available symbols to maximize the extrinsic probability values, with decoding employing a stored list of candidate points for discovered within a search radius, the list comprising the solution points found within the smallest radii.

Abstract: A method and apparatus for reducing the number of erred bits in the decoded signal by using a channel decoder whose transfer characteristic is matched to the transfer characteristic of the MIMO detector. This means that the curve of the transfer characteristic of the MIMO detector is 1) above the curve of the reflected transpose of the transfer characteristic of the channel decoder for about 95% of the curve, and 2) close to the reflected transpose of the curve of the transfer characteristic of the channel decoder. Particularly, an LDPCC decoder can be used as the channel decoder and can be matched to the MIMO detector by matching 1) the transfer characteristic of the LDPCC decoder's CND to 2) the transfer characteristic of a combination of the MIMO detector and the LDPCC VND. Furthermore, the LDPCC can be similarly matched to any appropriate detector in addition to or instead of the MIMO detector.

Abstract: A decoding scheme for determining the information within a coded transmission includes a spherical decoder candidate search that reduces the number of candidate symbol combinations from a much larger number of possibly transmitted combinations. In one example, the spherical decoder uses an upper triangular matrix representation of the channel matrix as part of a recursive, cumulative cost function that provides the results of the candidate search. The candidate search includes considering symbols in a hierarchy or tree structure that represents the possibly transmitted combinations. The cost function incrementally accumulates a cost of a possible combination as the search progresses through the hierarchy. As soon as a symbol is determined to not be a valid candidate, all possible combinations including that symbol are discarded without considering them, directly.

Abstract: A method and apparatus for reducing the number of erred bits in the decoded signal by using a channel decoder whose transfer characteristic is matched to the transfer characteristic of the MIMO detector. This means that the curve of the transfer characteristic of the MIMO detector is 1) above the curve of the reflected transpose of the transfer characteristic of the channel decoder for about 95% of the curve, and 2) close to the reflected transpose of the curve of the transfer characteristic of the channel decoder. Particularly, an LDPCC decoder can be used as the channel decoder and can be matched to the MIMO detector by matching 1) the transfer characteristic of the LDPCC decoder's CND to 2) the transfer characteristic of a combination of the MIMO detector and the LDPCC VND. Furthermore, the LDPCC can be similarly matched to any appropriate detector in addition to or instead of the MIMO detector.

Abstract: A transmission system is disclosed in which a multilevel modulated signal is transmitted. The soft output information of a channel decoder is fed back and utilized by a soft demapping device in order to improve the decoding result by further iterative decoding steps. The receiver includes a demapper for generating a demapped signal, bit deinterleaver for generating a demapped and deinterleaved signal and a decoder for generating soft reliability values representative of the decoded signal. These soft reliability values are then bit interleaved and fed back to the demapper, as a priori knowledge, for use in further iterations of the decoding process. Two mappings are mixed adaptively dependent on the channel conditions and the number of iterations to be used.

Abstract: An iterative decoder for serially concatenated encoded data in which an outer code is a rate 1:2 repetition code operative to encode a data bit bn as two identical and interleaved coded bitsbcoded,n0,bcoded,n1. The decoder comprises a soft-input, soft-output inner decoder for which the input and output information are log likelihood ratios, input information being the log likelihood ratios of the encoded data and outer extrinsic information. Feedback outer extrinsic information is substracted from the inner decoder output information to produce inner extrinsic information. The log likelihood ratios Lno,Ln1, in the inner extrinsic information, corresponding to one information bit bn, are swapped to produce the feed back extrinsic information. The pairs of log likelihood ratios Ln0,Ln1 of the inner extrinsic information are summed to make a hard decision for the correspoding information bit.

Abstract: Techniques for transmitting and receiving signals using a linear propagation channel, and the detection and decoding of the signals, are described. The symbols are decoded by computing the likelihood of each bit in a block of data in light of all blocks of received complex data and the constraints imposed by the channel code. Extrinsic information and a priori information are exchanged in an iterative fashion until desired performance is achieved. Extrinsic probability values are computed by searching through hypotheses in the constellation of available symbols to maximize the extrinsic probability values, with decoding employing a stored list of candidate points for discovered within a search radius, the list comprising the solution points found within the smallest radii.