TRELLIS-CODED CONSTANT-ENVELOPE MODULATIONS WITH LINEAR RECEIVERS

We present two multilevel constant-envelope continuous-phase modulatio n (CPM) schemes with four-dimensional (4-D) trellis coding, The receiv er is composed of a simple quadrature demodulator, followed by a symbo l-fate sampler and a Viterbi decoder matched to the code trellis, The first modulation is a quaternary CPM scheme whose phase transitions ov er a symbol interval are those of pi/4-shift quaternary phase-shift ke ying (QPSK), The demodulator filter is optimized so as to minimize the combined effect of intersymbol interference (ISI) and noise at the de cision instants, We use Wei's 16-state 4-D trellis code, and redefine the set partitioning tree so as to maintain the same minimum distance between parallel transitions as in quadrature amplitude modulation (QA M) signal sets, The resulting modulation outperforms minimum-shift key ing (MSK) by as much as 3.5 dB, in addition to reducing the 30-dB sign al bandwidth by 20%, Next, we introduce an octonary (8-level) CPM sche me whose phase transitions are those of pi/8-shift 8PSK, The same trel lis code and receive filter optimization are also applied to this modu lation which is shown to achieve better error rate performance than MS K, while saving some 60% of the transmitted signal bandwidth.