Abstract
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.
Highlights
The detection of a signal transmitted through a communication channel that contains intersymbol interference (ISI) and additive Gaussian noise has been widely studied for a broad range of channel models
bit error rates (BER) were obtained for several different systems using the predictive desired impulse response (DIR) MLSDVA architecture with time varying frequency selective fading channels
The performance of switched DIR systems to reduce the complexity of an maximum likelihood sequence detector Viterbi algorithm (MLSD-Viterbi algorithm (VA)) required for a range of dynamic channels has been investigated
Summary
The detection of a signal transmitted through a communication channel that contains intersymbol interference (ISI) and additive Gaussian noise has been widely studied for a broad range of channel models. This leads to the idea of using both of the optimal DIRs in a receiver structure It has been shown [10, 11] that rather than using a single adaptive prefilter together with an adaptive DIR, it is preferable to simultaneously operate two adaptive prefilters, each attempting to equalise the channel to one of the possible optimum DIRs. Each equaliser is followed by its own VA and at every symbol interval two decisions are produced. The final decision is made by a device that selects the symbol corresponding to the smaller of the two VA metrics We refer to this type of equaliser as switched dual DIR Viterbi equalisation.
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