THE EFFECT OF NONIDEAL INTERPOLATION ON SYMBOL SYNCHRONIZER PERFORMANCE

This contribution deals with the symbol synchronizer performance of a fully digitally implemented receiver, operating on a narrowband M-PSK signal (one-sided bandwidth not exceeding the symbol rate). The consid ered digital receiver operates on samples of the complex envelope r(t) of the received signal, taken by a fixed clock which is not synchroni zed to the transmitter clock. The synchronized samples required for th e symbol synchronization algorithm are computed by interpolating betwe en the available non-synchronized samples. Because of finite memory, i nterpolation is non-ideal; hence, some amount of distortion is introdu ced, which affects the performance of the symbol synchronizer. By mean s of theoretical analysis, we investigate the tracking performance of a specific decision-directed feedback synchronizer, assuming interpola tion of orders zero, one and two. We show that non-ideal interpolation gives rise to a loop noise spectrum containing spectral lines, that m ainly occur near f = 0 when the number of samples per symbol is close to an integer. Unless a sufficiently small loop bandwidth is chosen, t he contribution of these spectral lines could dominate the timing erro r variance, which then becomes much larger than for synchronized sampl ing.