A digital Rayleigh fade compensation technique for coherent IJF-OQPSK systems

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Abstract
A digital pilot-symbol-aided Rayleigh fade compensation technique for coherent intersymbol interference-jitter-free offset quadrature phase shift keying (IJF-OQPSK) is proposed. Instead of a fixed valued pilot symbol sequence, a scrambled pilot symbol sequence is transmitted to measure, and therefore to compensate for, the Rayleigh fading channel. The bit error rate (BER) performance of this system is investigated in fast Rayleigh fading, additive white Gaussian noise (AWGN), and cochannel interference (CCI) environments by using computer simulation. The simulated results show that a 2.5 dB improvement is achieved over the differentially detected pi /4-DQPSK at a BER of 10/sup -3/. Unlike the differentially detected pi /4-DQPSK, the system does not have an error floor or residual bit error, provided that the frame length N is not longer than the upper limit of frame length, N/sub max/. Another significant advantage is that the proposed IJF-OQPSK modulated signal is shown to suffer less spectral spreading than pi /4-QPSK signaling over a nonlinearly amplified channel.<>

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