ANALYTIC AND NUMERIC MODELING OF OPTICAL-FIBER PPM SLOT AND FRAME SPECTRAL PROPERTIES WITH APPLICATION TO TIMING EXTRACTION

An original numeric model is established and used to predict the spectral properties of optical fibre PPM. A suitable random variable is built into the model and used to represent the stochastic data sequence encoded. The spectral prediction is then used to examine the problems of slot and frame synchronisation in PPM. Slot synchronisation is investigated and optimised under dispersive and nondispersive optical fibre channels. The effect of the modulation index and the other PPM parameters on frame synchronisation is examined. A technique for spectral smoothing is presented and analysed while applied to the predicted spectra. To complete the study, an original analytic spectral characterisation is developed for the optical fibre PPM format. Use is made of the format cyclostationary properties. Both slot and frame synchronisation are considered. The results reveal the impact of the pulse shape, the data probability distribution, the modulation index and the PPM number of slots on the system synchronisation, thus enabling the identification of the optimum set of parameters. Practical results measured on a PPM system are presented on the slot and frame levels. Good agreement is observed between the numeric results, the analytic results and the practical measurements carried out, thus validating the models and enabling the identification of the optimum PPM system synchronisation parameters.