PHASE-LOCKED LOOP SYNCHRONIZATION FOR OPTICAL PPM COMMUNICATION SYSTEMS.

Summary form only given. For an M-ary optical PPM system which transmits square pulses that occupy the entire signal time slot, it can be shown that the output of the photodetector does not contain a spectral component at the slot frequency. Consequently, nonlinear processing of the photodetector output is needed to generate the required slot frequency component. This is accomplished by filtering the photodetector output and then squaring the result. The output of the squarer is then fed to the PLL. The performance of the PLL can be analyzed using a perturbation technique. The analysis shows that the phase variance is inversely proportional to the signal photocount and proportional to M, the number of time slots per word. The theoretical results are shown to be in good agreement with computer simulations of the PLL performance.