SISO Based Turbo Equalization and Decoding for ISI Corrupted Wireless Channels

The maximum a posteriori (MAP) probability algorithm and the soft output Viterbi algorithm (SOVA), usually known as soft in soft out (SISO) algorithms are used for data detection in non minimum phase channels representative of an outdoor cellular wireless environment. The performance of combinations of MAP and SOVA based equalizer and decoder is evaluated by simulation experiment. The performance does not improve much for more than five iterations in a severe ISI channel. The results obtained for 1 dB to 4 dB bit energy to noise power show that almost identical results are obtained for two other combinations of the SOVA and MAP in a serial concatenated scheme to take care of ISI. Theoretical analysis seems to support the viewpoint that all 4 possible combinations of MAP and SOVA algorithms result in an almost identical performance towards higher iteration numbers. Hence, SOVA-SOVA combination may be more suitable from implementation point of view than the other 3 combinations