Pilot symbol assisted modulation (PSAM) achieves coherent demodulation in a fading environment by inserting known symbols into the data stream. The receiver uses these pilot symbols to estimate its amplitude and phase reference. Although the pilots are typically spaced uniformly, adding extra consecutive pilot symbols allows one to estimate a large frequency offset on the channel. This work uses computer simulations to investigate the bit error probability (BEP) of PSAM with various non-uniform frame structures. It is shown that for higher Doppler rates, a non-uniform frame structure yields a lower BEP than a comparable uniform frame. Furthermore, in the presence of an unknown frequency offset, a non-uniform frame performs much better because it can estimate and remove the frequency offset prior to compensating for the fading process.

This paper investigates the affect of a frequency offset on the bit error probability of pilot symbol assisted modulation in frequency non-selective slow Rayleigh fading. Traditionally, the Wiener filter is designed to estimate both the fading induced multiplicative distortion and the frequency offset. However, it is shown that altering the frame structure to include consecutive pilot symbols and compensating for the frequency offset prior to Wiener filtering greatly improves the system performance.

Pilot-symbol-assisted modulation (PSAM) is a method to reduce the effects of fading in mobile communications by periodically inserting known symbols in the data stream. The receiver uses these pilot symbols to derive its amplitude and phase reference. One aspect of this procedure which has not received much attention in the literature is the method used by the receiver to locate the pilot symbols. This paper uses optimum frame synchronization techniques to develop two synchronizers for PSAM systems; one is based on a standard maximum likelihood (ML) estimation formulation, and the other is a sequential testing algorithm. Both methods use a simple quadratic correlation filter with an energy correction factor. Simulation results and a theoretical analysis are presented.