Performance of PLL-based optical OPPM communication systems

The power spectral density (PSD) of a direct-detected optical signal with overlapping pulse-position modulation (OPPM) scheme is derived. It is demonstrated that this spectrum contains a strong periodic component at the signal symbol frequency, thereby enabling a simple PLL device to provide joint symbol and slot synchronization. The variance of the timing error for a linearized PLL synchronizer is shown to be mainly dominated by, and is inversely proportional to, the product of the PLL closed-loop bandwidth and symbol duration of the OPPM signal. The performance of a shot-noise limited PLL-based optical OPPM communication system is then assessed in terms of the overall system symbol error rate