An analysis of pilot symbol assisted QPSK for digital mobilecommunications

摘要

Embedded pilot symbols, which provide an amplitude and phasereference to mitigate the effects of rapid fading in mobilecommunications, are discussed. It is shown that, unlike the pilot tonesystems, pilot symbol assisted modulation (PSAM) does not affect thetransmitted pulse shape or the peak-to-average power ratio, andimplementation is straightforward. Closed-form expressions are presentedfor the optimized receiver coefficients, and for the bit-error rate(BER) in binary phase-shift keying (BPSK) and quadrature phase-shiftkeying (QPSK) or π/4-offset QPSK. It is also shown that the errorrates obtained are lower than those for differential detection for anycombination of signal-to-noise ratio (SNR) and Doppler spread, and theperformance is within 1 dB of a perfect reference system under slowfading conditions and within 3 dB when the Doppler spread is 5% of thesymbol rate