Abstract: In an embodiment a method of generating an erasure code for a network comprising a plurality of nodes, wherein the nodes of the network store data symbols and the number of data symbols stored on a first node of the network is different from the number of data symbols stored on a second node of the network, the erasure code indicating the dependance of parity symbols stored by the nodes of the network on the data symbols such that the data symbols stored on nodes of the network can be determined from parity symbols and data symbols stored on other nodes of the network, comprises determining from the distribution of data symbols among the nodes, an optimal parity symbol distribution;based on the optimal parity symbol distribution and the distribution of data symbols, selecting a code generation method; and generating the erasure code using the selected code generation method.

Abstract: According to one embodiment, antenna allocation or selection in a multi-antenna wireless communications device can be performed at a receiver or an emitter of a wireless communications signal. Selection takes place on the basis of antenna and frequency. Antenna selection in a disclosed embodiment involves a combination of bulk and per tone antenna selection.

Abstract: According to an embodiment a decoder for decoding a received set of blocks each comprising a plurality of data symbols and a plurality of parity symbols, wherein the received set of blocks is a subset of a complete set of blocks, the complete set of blocks comprising at least one erased block not included in the received set of blocks comprises storage for a coding matrix which is the kronecker product of a totally non-singular matrix with an anti-diagonal matrix; and a processor operable to determine data symbols of the at least one erased block using the encoding matrix.

Abstract: In an embodiment a method of estimating a sparse signal from a measured signal using a transform matrix is disclosed. The method comprises determining a partial contribution to the sparse signal; determining a residual by subtracting the partial contribution from the measured signal; and iteratively determining further contributions to the sparse signal.

Abstract: Channel estimation in a MIMO communications system includes performing a decomposition of an initial channel matrix estimate associated with a first subcarrier of a plurality thereof defined in the channel to identify eigenvectors associated with that subcarrier of the received signal, and defining a first beamforming transformation to be applied to the received signal on the basis of the eigenvectors. For each of the other subcarriers, an additional decomposition is performed in order to determine a further beamforming transformation for each subcarrier. The additional decompositions are carried out incrementally such that information determined in one of said decompositions contributes to a later executed decomposition. Further described is a method of transmitting from a multiple antenna transmitter defining a plurality of subcarriers in space, and time or frequency, comprising the same iterative process.

Abstract: Allocation of subcarriers of a wireless communications channel to antennas for transmission of said subcarriers from a multi-antenna transmitter, comprises selecting, for each subcarrier, the antenna with the most effective transmission performance against a predetermined performance criterion; and determining if subcarriers are evenly distributed amongst said antennas. If even distribution does not arise, then a reallocation sequence is performed. This comprises identifying, for an antenna having excessive subcarriers allocated thereto, the subcarriers allocated thereto and reallocating one of said subcarriers as required, said reallocated subcarrier being selected for reallocation on the basis of its impact on transmission performance.

Abstract: Precoding a plurality of subcarriers in preparation for MIMO transmission is carried out by deriving preceding matrices from available information. When the number of data streams borne by the subcarriers equates to the number of transmit antennas employed in the MIMO transmission, the method comprises deriving, from respective acquired unitary precoder matrices for two of said subcarriers, interpolated precoder matrices for data streams intermediate the two subcarriers. The acquired and interpolated precoder matrices are then applied, as the case may be, at the respective subcarriers.

Abstract: A method and device for managing the use of antennas in a multiple antenna wireless transmission system for OFDM signals. The method includes defining a utility function which comprises a performance metric for transmission. Combinations of antenna and OFDM subcarriers are selected to optimize the utility function under two constraints. The first constraint is that the combinations of antenna and subcarrier include only one antenna for each subcarrier, the second constraint is that the combinations include the same number of subcarriers for each antenna.

Abstract: According to one embodiment, antenna allocation or selection in a multi-antenna wireless communications device can be performed at a receiver or an emitter of a wireless communications signal. Selection takes place on the basis of antenna and frequency. Antenna selection in a disclosed embodiment involves a combination of bulk and per tone antenna selection.

Abstract: The present invention relates to estimating and correcting for frequency offset errors in wireless receivers, and is particularly but not exclusively related to MIMO WLAN applications. The present invention provides an improved method of tracking receiver frequency offsets in a receiver for MIMO systems. These receiver based frequency offset components are caused by errors or inaccuracies in various receiver sub-systems such as phase lock loops or carrier frequency oscillator error, and sampling clock rate errors. The frequency offsets due to each of a number of receiver sub-systems are estimated by monitoring frequency offsets on a number of channels or subcarriers (such as OFDM pilot channels) on different frequencies. These channel frequency offsets are preferably estimated by detecting the phase rotation between adjacent pilot symbols on each respective channel. They are then weighted according to a quality parameter of the estimates, which corresponds to their accuracy.

Abstract: Allocation of subcarriers of a wireless communications channel to antennas for transmission of said subcarriers from a multi-antenna transmitter, comprises selecting, for each subcarrier, the antenna with the most effective transmission performance against a predetermined performance criterion; and determining if subcarriers are evenly distributed amongst said antennas. If even distribution does not arise, then a reallocation sequence is performed. This comprises identifying, for an antenna having excessive subcarriers allocated thereto, the subcarriers allocated thereto and reallocating one of said subcarriers as required, said reallocated subcarrier being selected for reallocation on the basis of its impact on transmission performance.

Abstract: The invention provides a method and device for managing the use of antennas in a multiple antenna wireless transmission system for OFDM signals. The method includes defining a utility function which comprises a performance metric for transmission. Combinations of antenna and OFDM subcarriers are selected to optimise the utility function under two constraints. The first constraint is that the combinations of antenna and subcarrier include only one antenna for each subcarrier, the second constraint is that the combinations include the same number of subcarriers for each antenna.

Abstract: Precoding a plurality of subcarriers in preparation for MIMO transmission is carried out by deriving preceding matrices from available information. When the number of data streams borne by the subcarriers equates to the number of transmit antennas employed in the MIMO transmission, the method comprises deriving, from respective acquired unitary precoder matrices for two of said subcarriers, interpolated precoder matrices for data streams intermediate the two subcarriers. The acquired and interpolated precoder matrices are then applied, as the case may be, at the respective subcarriers.

Abstract: Channel estimation in a MIMO communications system comprises performing a decomposition of an initial channel matrix estimate associated with a first subcarrier of a plurality thereof defined in the channel to identify eigenvectors associated with that subcarrier of the received signal, and defining a first beamforming transformation to be applied to the received signal on the basis of the eigenvectors. Then, for each of the other subcarriers, an additional decomposition is performed in order to determine a further beamforming transformation for each of said one or more other subcarriers, wherein said additional decompositions are carried out incrementally such that information determined in one of said decompositions contributes to a later executed decomposition. Further described is a method of transmitting from a multiple antenna transmitter defining a plurality of subcarriers in space, and time or frequency, comprising the same iterative process.

Abstract: Detection of information on an OFDM signal involves channel estimation. Following an initial channel estimate, it is desirable to perform smoothing or filtering to achieve a more effective channel estimate. A filter is described which is operable to smooth an initial estimate for a subcarrier by reference to one or more adjacent subcarrier estimates. Extrapolation is used to impose, on a subcarrier, information dependent on one or more other subcarriers in the case that the subcarrier in question is not in use other than use by the filter.

Abstract: In a lattice-reduction-aided receiver based wireless communications system, outputs are determined on the basis of a received signal, the received signal being modulated onto a plurality of sub-carriers.

Abstract: In a lattice-reduction-aided receiver based wireless communications system, soft estimates of transmitted bit values are determined from a received signal by applying lattice reduction to the channel estimate and equalising the received signal in accordance with the reduced basis channel, and determining probabilities of transmitted bits having particular values. The method includes selecting an initial candidate vector in the reduced basis and determining further candidate vectors in the reduced basis dependently of the initial candidate vector, determining a corresponding transmitted symbol vector for each candidate vector and, on the basis of the received signal determining the probability of each transmitted bit value having been transmitted and log-likelihood ratios of transmitted bits.