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UBC Theses and Dissertations

Noncoherent detection for differential offset QPSK Ho, Ivan Chit Hin

Abstract

At the physical layer of wireless communication systems, differential offset quaternary phase-shift keying (DOQPSK) offers a great avenue for low-cost implementation. However, its unfavorable error performance with conventional differential detection (DD) has made DOQPSK unpopular in practical use. Recently, Dr. M. Simon proposed a multiple-bit differential detection (MBDD) scheme that is derived from optimal maximum-likelihood block detection (MLBD) [1]. Asymptotically, MBDD still suffers a 3 dB loss in power efficiency compared to that of coherent detection (CD). To close the performance gap between MBDD and CD, and to make the receiver a simple and versatile solution, five novel noncoherent receiver designs for DOQPSK are proposed in this thesis: full-size MBDD (F-MBDD), improved MBDD (I-MBDD), noncoherent linear equalization (NLE), noncoherent decision-feedback equalization (NDFE), and noncoherent sequence estimation (NSE). In F-MBDD, we use an appropriate model for the overall channel to overcome the performance gap of Simon's receiver. I-MBDD improves the slow convergence of the error value in F-MBDD by truncating the detection window size from N — 1 to N — 3. For NLE and NDFE, computational complexity is reduced by employing suboptimal equalization techniques to suppress inter-symbol interference (ISI) introduced by the OQPSK modulation. Finally, NSE uses ML detection with a trellis decoder that is based on the Viterbi algorithm (VA). When designed carefully, all the schemes proposed in this work have shown performances close to that of CD. In addition, receiver parameters can be controlled to balance performance, complexity, and versatility.

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