Enhancing Signal Detection in Frequency Selective Channels by Exploiting Time Diversity in Inter-symbol Interference Signal

Inter-symbol interference (ISI) causes many errors in modulated symbols, when they are transmitted through band-limited channels. According to the multipath delay profile of the channel, the modulated symbol may disperse over more than one symbol period casing interferences among the received symbols. In this paper, the ISI signal is not considered as a problem, but it is exploited as a source of time diversity for the modulated symbols. The ISI signal is considered as if the modulated symbols are transmitted more than one time through different symbols periods. The number of periods over which the modulated symbol extends, represents the time diversity gain of the proposed system. In the proposed receiver, the interfering symbols are considered as symbols from different users. A multiuser detector is used to demodulate these interfering symbols. Moreover, a signal combiner is used to collect the detected symbol from the output of the multiuser detector through the dispersion period of the channel. The output of the combiner represents the decision variable to the baseband detector. The diversity gain in the decision variable in the proposed receiver is proportional to the dispersion period of the channel.