The effect of non-ideal interpolation on symbol synchronization performance

Deals with the symbol synchronization performance of a fully digitally implemented receiver, operating on a narrowband M-PSK signal (one-sided bandwidth not exceeding the symbol rate). The considered digital receiver operates on samples of the complex envelope r(t) of the received signal, taken by a fixed clock which is not synchronized to the transmitter clock. The synchronized samples required for the symbol synchronization algorithm are computed by interpolating between the available non-synchronized samples. In the case of non-ideal interpolation, some amount of distortion is introduced, which affects the performance of the symbol synchronizer. By means of theoretical analysis, the authors investigate the tracking performance of a specific decision-directed feedback synchronizer, assuming interpolation of orders zero and one. They show that non-ideal interpolation gives rise to a loop noise spectrum containing spectral lines, that mainly occur near f=0. Hence, a sufficiently small loop bandwidth is required to suppress these spectral lines