Performance analysis of coded optical ppm system using direct and coherent detection

Abstract
Monomode optical fibres currently used in optical communication systems usually have bandwidths much greater than the information rate transmitted. This excess bandwidth can be used to improve receiver sensitivity. Pulse-position modulation (PPM) schemes are usually used in optical communication systems to improve receiver sensitivity. The paper analyses the sensitivity of the receiver of an optical PPM system, considering both wrong-slot error and false-alarm error. Coded optical PPM systems with direct and heterodyne detection are analysed. The performances of Reed-Solomon codes with different code rates are considered. Relations between bit-error probability Pb and the optimum efficiency p for the uncoded and coded systems are obtained. It is found that system performance does not necessarily improve with coding. System performance improves only for codes that are capable of reducing the minimum required number of photons sufficiently to compensate for the decrease in system efficiency resulting from coding.

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