Optical fibre n-ary PPM: natural acquisition sequences and frame phase extraction

A novel frame phase extraction technique is presented and analysed in the context of optical fibre PPM. Two classes of naturally occurring PPM sequences are identified and used to acquire the frame phase information directly from the incoming data stream. The technique is superior to previous methods since it does not entail added code redundancy, complex coders and decoders or loss in sensitivity and bit rate. Additionally the frame phase synchronisers are shown to be upgradable and thus capable of coping with the required PPM word size. Original theoretical and practical results are reported for the synchronisers predicting an improvement of 6 dB in the discrete frame spectral component whenever the sequences tracked are doubled, with a corresponding 6.2×10^-3 rad² reduction in the timing variance