The paper presents a Euclidean distance maximum likelihood sequence estimation (MLSE) receiver, based on the Viterbi algorithm (VA), suitable for fading and noisy communications channels, as that specified by the Group Special Mobiles (GSM). In a mobile cellular system, the fast varying channel characteristics, due to the fading and Doppler effects, require adaptive methods to update the channel coefficients to the MLSE receiver. The proposed technique continuously estimates the channel characteristics directly within the metric calculation of the VA. At each step of the VA, the sequence associated to the path with the best metric value (minimum-survivor method) among the survivor paths is used to update the channel estimate (employing conventional adaptive algorithms) throughout the entire informative sequence. However, the detection of the transmitted data sequence is performed by the VA only at the end of each burst. The proposed technique allows simpler receiver implementation and the simulation results show a good performance of this adaptive MLSE receiver in typical GSM environments.

A simplified structure concerning the implementation of an adaptive digital receiver suitable for the pan-European cellular system Group Special Mobile (GSM) is described. In the GSM system, the performance of the received information is strongly affected by the multipath typical of the mobile communications channel. The proposed maximum-likelihood sequence estimation (MLSE) receiver based on the Viterbi algorithm compensates for selective distortion due to the multipath propagation and Doppler shift also in the case of fast channel variations using an adaptive tracking mode method.>