Robust M-PSK phase detectors for carrier synchronization PLLs in coherent receivers: theory and simulations

In this paper we present two new Non Data Aided (NDA) phase detectors (PDs) for carrier synchronization Phase Locked Loops (PLLs) in M-ary Phase Shift Keying (M-PSK) receivers. The first structure is a self-normalizing modification of the M-th order nonlinearity detector. We investigate this detector theoretically in order to predict its S-curve, self-noise, squaring-loss, and phase-error variance performance. These theoretical predictions are then verified by computer simulations, and the results are contrasted with results obtained using other NDA and Decision Directed (DD) phase detectors. As those comparisons show, the proposed structure offers improved phase-error variance performance that is robust to Automatic Gain Control (AGC) circuit imperfections. Moreover, the new detector has a compact hardware structure suitable for implementation within an FPGA or ASIC. The second phase detector structure presented is an adaptive detector whose principal novelty is that it dynamically adapts the phase detector's gain to allow the PLL to perform optimally at any input Signal-to-Noise Ratio (SNR) at which it can lock. This detector is also robust vis-a-vis the AGC and has a compact hardware implementation suitable for FPGAs and ASICs.