The N-Phase Digital Tanlock Loop for Tracking Suppressed-Carrier N-ary PSK Signals

In this paper, the performance of anN-phase digital tanlock loop (DTL) in the presence of phase error disturbance is studied. TheNphase DTL is a digital loop for tracking suppressed-carrierN-ary phaseshift keyed (PSK) signals. It has linear phase characteristics in the modulo-2π/Nsense as a result of using thetan⁻¹[.]function in the phase error detector. We first obtain the probability density function of phase error of the phase detector output and verify it by computer simulation. Then, we consider the optimum bandwidths of the bandpass filters in the loop that yield the minimum variance of the phase error. Also, the finite word length effect on the performance of theN-phase DTL is investigated by computer simulation. In addition, the performance of theN-phase DTL is compared to that of the digitalN-phaseI-Qloop which has sinusoidal phase characteristics. It has been found that the first-order Nphase DTL has wider lock range than the first-orderN-phaseI-Qloop in the absence of noise.