This is because in case of short buffers, ie. As the buffer size is increased, the high-order coefficients of the polynomial interpolator diminish and hence increasing the buffer size becomes less significant. On the same note, as the buffer size increases, the impulse response of the low pass interpolator becomes more like that of an ideal Sinc function and therefore its performance improves. Surprisingly, for BPSK at an SNR of 20 dB, the differential scheme has actually a marginally better BER performance than the corresponding PSAM scheme, even when disregarding the proportion of power allocated to the pilots. The shortest system delay and lowest complexity amongst the PSAM schemes was associated with the one employing the first-order linear interpolator.
Future work is targeted at a similar study of block-coded modulation schemes.
IEEE Tr. on Veh. Techn. , Vol. Conf. , San Francisco, CA, May 1989, pp.