A study of non-uniform pilot spacing for PSAM

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