Dual Switched Predictive DIR MLSD Receiver for Dynamic Channels

A linear prefilter can be used to reduce the required complexity of a maximum likelihood sequence detector Viterbi algorithm (MLSD-VA) by shortening the overall channel and prefilter impulse response in dynamic communication systems. The combination of channel and prefilter should have the effect of producing a desired impulse response (DIR) at the detector. Falconer and Magee (1973) showed that for a finite length DIR there are a limited number of possible DIRs that are optimal. For a DIR of length two symbols, there are only two optimal DIRs, for a length three DIR there exists a range of possibly optimal DIRs. In this paper, we present a novel receiver architecture in which we use two equalisers and two Viterbi detectors. Each equaliser has a different target DIR. A selection device chooses between the output of the two VAs. It is demonstrated that, using the two optimal length two DIRs can be preferable to both switched triple DIR system and adaptive DIR strategies. It is also demonstrated in this paper that there exists a range of environments where adaptive DIR MLSD-VA receivers fail, however the proposed dual switched DIR MLSD-VA is successful in these environments. The efficacy of the switched dual DIR MLSD-VA is also shown using doubly selective fading channels.