High speed equalizer for GSM/GPRS

In mobile communication the equalizer removes intersymbol interference (ISI) introduced by the multipath fading signals. Sequence estimation algorithms are used in the equalizer for their better performance. MLSE is one such sequence estimation technique in which the Viterbi algorithm is used. In this work, we propose various optimizations, which bring down the computational complexity and memory requirements significantly for the GSM/GPRS equalizer. The redundancies in the computation of branch metrics and trace-backs are avoided in the optimizations. This equalizer can be implemented on any general purpose DSP, as the optimizations are performed on the algorithm and are not specific to any processor. These optimizations resulted in 66% reduction in arithmetic computations per Viterbi butterfly. On TMS320C55x, the proposed implementation takes only 3.4 million cycles per second (MCPS) whereas the state of art implementation takes 12 MCPS.