Methods and systems for estimating and mitigating OFDM interference to enable reliable communications with minimal a priori knowledge of the interfering OFDM signal are presented. Embodiments of the present invention hypothesize modulation symbols from a reference signal set, which may not be identical to the interference signal set, and compute a channel sequence to minimize an error between the observed samples and a product of the channel sequence and the hypothesized modulation symbols. The interfering OFDM signal may be estimated and mitigated with no reliance on knowledge of the interference signal set, although this may result in the inability to decode and demodulate the interfering OFDM signal when embodiments of the present invention are extended from single-input single-output systems to multiple-input single-output systems.

There is provided a decoder (310) for sequentially decoding a data signal received through a transmission channel in a communication system, the received data signal carrying transmitted symbols, the decoder comprising a symbol estimation unit (311) configured to determine estimated symbols representative of the transmitted symbols carried by the received signal from information stored in a stack, the stack being filled by iteratively expanding child nodes of a selected node of a decoding tree comprising a plurality of nodes, each node of the decoding tree corresponding to a candidate component of a symbol of the received data signal and each node being associated with a predetermined metric, the stack being filled at each iteration with at least some of the expanded child nodes and being ordered by increasing values of the metrics associated with the nodes, the selected node for each iteration corresponding to the node having the lowest metric in the stack. The decoder further comprises a stack reordering activation monitoring unit (313) configured to monitor at least one stack reordering activation condition and, in response to a stack reordering activation condition being verified, to cause the symbol estimation unit to: reduce the metric associated with each node stored in the stack by a quantity, reorder the stack by increasing value of the reduced metric, and remove a set of nodes from the reordered stack so as to maintain a number N of nodes in the reordered stack, the maintained nodes corresponding to the N nodes having the lowest metrics in the reordered stack.

An error detection and correction device includes a decision-feedback equalizer (DFE), a decision circuit, an error detection circuit, and an error correction circuit. The DFE equalizes a data signal to generate a first equalized signal. The decision circuit performs hard decision upon the first equalized signal to generate a symbol decision signal. The error detection circuit performs forward error detection at symbol positions of consecutive symbols included in the symbol decision signal to detect a head position of suspicious error that affects at least one symbol in the symbol decision signal. The error correction circuit performs error correction upon the symbol decision signal in response to the head position of the suspicious error that is detected by the error detection circuit.

Sequence detectors and detection methods are provided for detecting symbol values corresponding to a sequence of input samples obtained from an ISI channel. The sequence detector comprises a branch metric unit (BMU) and a path metric unit (PMU). The BMU, which comprises an initial set of pipeline stages, is adapted to calculate, for each input sample, branch metrics for respective possible transitions between states of a trellis. To calculate these branch metrics, the BMU selects hypothesized input values, each dependent on a possible symbol value for the input sample and L>0 previous symbol values corresponding to possible transitions between states of the trellis. The BMU then calculates differences between the input sample and each hypothesized input value. The BMU compares these differences and selects, as the branch metric for each possible transition, an optimum difference in dependence on a predetermined state in a survivor path through the trellis.

In a spatial modulation multiple-input-multiple-output (SM-MIMO) wireless communication system, multiple transmitting antennae and multiple receiving antennae may be utilized to respectively transmit and receive wireless signals for the communication. A selection of a combination of the multiple transmitting antennae may be configured to represent one or more binary digits in a signal sequence. The signal sequence may be produced at the receiving end without the knowledge of the selection of the combination of the multiple transmitting antennae.

A digital signal processing method and apparatus is described. The digital processing apparatus comprises a coarse carrier recovery module for performing a coarse carrier compensation of a received modulated signal; and a trellis-based equalization module selectable between a first mode for performing a trellis-based equalization to compensate a residual inter-symbol interference of the received modulated signal and a second mode for performing a trellis-based equalization to compensate a residual phase noise of the received modulated signal.

Quasi-reduced state trellis equalization techniques achieve low-latency inter-symbol interference (ISI) equalization by selecting a subset of accumulated path metrics (APMs) for a leading symbol to propagate over a trellis to candidate states of a trailing symbol. This simplifies the computation of APMs for candidate states of the trailing symbol. Thereafter, APMs for candidate states of the trailing symbol are computed based on the subset of APMs for the leading symbol that were propagated over the trellis. Propagating fewer than all APMs for the leading symbol to the trailing symbol reduces the complexity of APM computation at the trailing symbol.

Systems (100) and methods for co-channel separation of communication signals. The methods involve: simultaneously receiving a plurality of communication signals transmitted at disparate relative Doppler frequencies from different locations within a multi-access system; performing matched filtering operations to pre-process each of the plurality of communication signals so as to generate pre-processed digitized samples using a priori information contained in pre-ambles (302, 304) of messages present within the plurality of communication signals; using estimated signal parameters to detect the plurality of communication signals from the pre-processed digitized samples; and demodulating the plurality of communication signals without using a Viterbi decoder.

The present invention relates to a method and apparatus for channel estimation between a transmitter and a receiver in a wireless communications system. In one arrangement, the method comprises: receiving at the receiver a first sequence of bits representing a first sequence of coded symbols transmitted over the communications channel; decoding the first sequence of coded symbols using maximum-likelihood based decoding including: generating traceback outcomes by tracing backwards the first sequence of bits through a maximum-likelihood based traceback path, the traceback outcomes including a first portion associated with a first traceback depth and a second portion associated with a second traceback depth that is deeper than the first traceback depth; generating a channel estimate of the communications channel based on the first portion of the traceback outcomes; and generating an estimate of at least some information bits coded in the first sequence of coded symbols based on the second portion of the traceback outcomes.

There is provided a decoder for sequentially decoding a data signal received through a transmission channel in a communication system, said data signal carrying transmitted symbols, said decoder comprising a symbol estimation unit (301) configured to determine estimated symbols representative of the transmitted symbols carried by the received signal from information stored in a stack, said symbol estimation unit (301) being configured to iteratively fill the stack by expanding child nodes of a selected node of a decoding tree comprising a plurality of nodes, each node of the decoding tree corresponding to a candidate component of a symbol of said data signal and each node being assigned a metric, the stack being filled at each iteration with a set of expanded child nodes and being ordered by increasing values of the metrics assigned to the nodes, the selected node for each iteration corresponding to the node being assigned the lowest metric in the stack, the decoder comprising a metric determination unit (302) configured to determine an initial metric for each child node of said set of expanded child nodes, wherein the decoder further comprises a modified metric calculation unit (303) configured to calculate a modified metric for at least one of the expanded child nodes from the metric associated with said expanded child node and a weighting coefficient, said weighting coefficient being a function of the level of said node in the decoding tree, the decoder assigning said modified metric to said at least one of the expanded child nodes.