Design and Performance of a New OQPSK Coherent Demodulator Using an Advanced Simultaneous Carrier and Bit-Timing Recovery SchemeApplication to Wireless ATM Systems

Masahiro UMEHIRA

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E80-A    No.7    pp.1175-1182
Publication Date: 1997/07/25
Online ISSN: 
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on Multi-dimensional Mobile Information Network)
coherent detection,  carrier recover,  bit-timing recovery,  OQPSK,  wireless ATM,  

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This paper presents a new offset-quadrature-phase-shift-keying (OQPSK) coherent demodulation scheme for wireless asynchronous transfer mode (WATM) systems that premise the Ricean fading communication channels (e.g., typically with derectional antennas). The presented demodulator is basically advanced from a simultaneous carrier and bit-timing recovery (SCBR) scheme by newly employing a phase compensated filter and a reverse-modulation scheme for OQPSK. This advancement aims to enhance the carrier phase tracking performance against the phase fluctuation due to the fading and/or the phase rotation caused by the carrier frequency error of the oscillator. Design consideration and performance evaluation of the demodulator are extensively carried out under Ricean fading channels typical of the WATM systems as well as additive white Gaussian noise (AWGN) channels. The evaluation ressults show that the advanced SCBR (ASCBR) scheme achieves a bit-error-rate/cell-error-rate (BER/CER) performance close to ideal coherent detection with a considerably short preamble, e.g., 8 symbols. Specifically, compared with differential detection (evaluated for QPSK with the hard-wired clock), the new coherent demodulator achieves a significant required Eb/No improvement, which becomes larger as the fading condition degrades. This paper concludes that the ASCBR scheme is a strong candidate for the Ricean-fading-premise WATM systems.