Advanced transceiver design for continuous phase modulation

Abstract

This dissertation proposes advanced transceiver designs applying turbo and space-time (ST) concepts to continuous phase modulation (CPM), which is preferred in numerous power- and band-limited communication systems for its constant envelope and spectral e ciency. Despite its highly attractive spectral properties, maximumlikelihood detection of CPM over the frequency-selective multipath fading channels can bring impractical complexity issues because of the intensive search over a single super trellis which combines the e ects of the modulation and the multipath channel. Application of the reduced-state trellis search algorithms results in lower complexity but the computational load could still be prohibitively large to obtain high performance in long channel impulse responses. In the dissertation, instead of employing trellis-based combined detection methods, equalization and demodulation functions are separated and novel low-complexity receivers with soft-input soft-output (SISO) time-domain and frequency-domain linear equalizers are proposed for bit-interleaved coded CPM, which attain near-optimal performance by applying turbo processing. In the proposed receivers, the front-end soft-information-aided linear equalizer is followed by a central SISO CPM demodulator and a back-end SISO channel decoder where double turbo processing is employed by performing back-end demodulation/decoding iterations per each equalization iteration to improve the a priori information for the front-end equalizer. Performance for the frequency-domain equalization is further improved by proposing an orthogonal ST block coding scheme for CPM. The proposed technique maintains the constant envelope and the phase continuity of the CPM waveforms perfectly by using appropriate tail symbols and, therefore, has no impact on the spectral e ciency. Depending on the orthogonality of the ST combining, frequencydomain equalization is applied as in the case of single antenna transmissions without v any increase in the computational load. In the dissertation, the receiver complexity is reduced further by transferring all the equalization functions to the transmitter and employing pre-equalization. For precoding the CPM signals on multipath fading channels while maintaining the spectral e ciency, a novel ST pre-equalizer is proposed, limiting the envelope variations and attaining a peak-to-average power ratio that is close to one by using a transmit selection diversity scheme.