Phase tracking loop in the underwater QPSK transmission

In this paper, we propose a design method for phase tracking loop with 2nd order loop filter, which can trace a small frequency variation as well as a phase variation. The loop parameter totally governs the traceable frequency range, the transient period and the phase fluctuating bound at the steady state. To determine the proper loop parameter, the proposed algorithm iteratively computes the loop parameter sets using the loop characteristics at the transient state and the steady state until the fluctuating bound of tracking phase error is less than the desired bound. After sequentially applying the computed parameter sets to the loop, the desired performance of phase tracker can be obtained when the symbol error rate is reasonably small.