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

A digital tanlock loop (DTL) is a nonuniform-sampling digital phase-lo cked loop (DPLL) whose phase error detector, using the tan-1[.] functi on with in-phase and quadrature samples of incoming signal, has a line ar characteristic with a period of 2pi. In this paper, we study the ap plication of an N-phase DTL in digital cellular radio with pi/4-DQPSK modulation. The performance degradation due to fading effect is invest igated in terms of bit error rate and steady state phase error varianc e by computer simulation. It is shown that, in the digital cellular ra dio system, the performances on both bit error rate and phase error va riance using DTL are far better than that using the traditional digita l N-phase I-Q loop.