ON REDUCED COMPLEXITY TECHNIQUES FOR BANDWIDTH EFFICIENT CONTINUOUS PHASE MODULATIONS IN SERIALLY CONCATENATED CODED SYSTEMS
AffiliationUniversity of Kansas
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AbstractSerially concatenated coded (SCC) systems with continuous phase modulations (CPMs) as recursive inner codes have been known to give very high coding gains at low operative signal to noise ratios (SNRs). Moreover, concatenated coded systems with iterative decoding approach the bit error rate (BER) bounds given by the maximum likelihood (ML) criterion. Although SCC systems by themselves are reduced complexity systems when compared to the ML decoding, when very highly bandwidth efficient CPMs such as pulse code modulation /frequency modulation (PCM/FM) is used , they present a problem of extremely high decoding complexity at the receiver. The complexity of a CPM is described by the size of its trellis which is a function of the modulation index, the cardinality of the source alphabet and the length of the frequency pulse used. The surveyed complexity reduction techniques adopt approximations which will reduce the size of the trellis with minimal expense of power. In this paper, we present reduced complexity approaches to sub-optimally decode SCC PCM/FM by mainly two approaches - 1) Frequency pulse truncation. 2) Decision feedback.
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