An analysis of pilot symbol assisted QPSK for digital mobile communications

Embedded pilot symbols, which provide an amplitude and phase reference to mitigate the effects of rapid fading in mobile communications, are discussed. It is shown that, unlike the pilot tone systems, pilot symbol assisted modulation (PSAM) does not affect the transmitted pulse shape or the peak-to-average power ratio, and implementation is straightforward. Closed-form expressions are presented for the optimized receiver coefficients, and for the bit-error rate (BER) in binary phase-shift keying (BPSK) and quadrature phase-shift keying (QPSK) or π/4-offset QPSK. It is also shown that the error rates obtained are lower than those for differential detection for any combination of signal-to-noise ratio (SNR) and Doppler spread, and the performance is within 1 dB of a perfect reference system under slow fading conditions and within 3 dB when the Doppler spread is 5% of the symbol rate