DIGITAL TANLOCK LOOP FOR TRACKING PI/4-DQPSK SIGNALS IN DIGITAL CELLULAR RADIO

Abstract

A digital tanlock loop (DTL) is a nonuniform-sampling digital phase-locked loop (DPLL) whose phase error detector, using the tan-1[.] function with in-phase and quadrature samples of incoming signal, has a linear characteristic with a period of 2pi. In this paper, we study the application of an N-phase DTL in digital cellular radio with pi/4-DQPSK modulation. The performance degradation due to fading effect is investigated in terms of bit error rate and steady state phase error variance by computer simulation. It is shown that, in the digital cellular radio system, the performances on both bit error rate and phase error variance using DTL are far better than that using the traditional digital N-phase I-Q loop.