Abstract: The attenuation and phase change of a communication channel have to be estimated for near-maximum-likelihood detection and this presents severe difficulties where rapid fading occurs especially in communication between mobile stations in cellular radio. A number of vectors are stored which represent possible sequences of received data symbols and these vectors are expanded on receipt of each further digital sample. Costs, representing a measure of the likelihood that sequences are correct, the lower the cost the higher the likelihood, are then derived for each vector on the basis of stored prediction of channel performance. Next the earliest data symbols in the vector with lowest costs are output as detected symbols and then the vectors with lowest costs are selected for storage in place of the original vectors. New channel predictions are formed from channel estimates for the current sample and stored for use in the next iteration.

Abstract: The attenuation and phase change of a communication channel have to be estimated for near-maximum-likelihood detection and this presents severe difficulties where rapid fading occurs especially in communication between mobile stations in cellular radio. A number of vectors are stored which represent possible sequences of received data symbols and these vectors are expanded on receipt of each further digital sample. Costs, representing a measure of the likelihood that sequences are correct, the lower the cost the higher the likelihood, are then derived for each vector on the basis of stored prediction of channel performance. Next the earliest data symbols in the vector with lowest costs are output as detected symbols and then the vectors with lowest costs as selected for storage in place of the original vectors. New channel predictions are formed from channel estimates for the current sample and stored for use in the next iteration.

Abstract: Filters are provided at the outputs of data transmission links to overcome attenuation distortion and phase distortion but such filters tend to increase the noise content of received signals. In the present invention a filter coupled to a linear baseband channel is constrained to be an all pass network, thus avoiding any noise enhancement at its output. The filter is adjusted using a channel estimator and an adjustment system to give the channel plus the filter an impulse-response that rises rapidly to its peak, thus simplifying the detection process needed for a satisfactory tolerance to noise.

Abstract: A method and apparatus for decoding received data signals using a Viterbi algorithm. To reduce the time required to decode a data signal, the system expands k received data vectors into nk vectors where n is smaller than m, m being the number of levels of the received data signal. Thereafter, k vectors are chosen from the nk expanded vectors and a "cost", defined herein is determined for each of said k vectors. The most likely identity of the received data signal is then determined on the basis of the computed costs.