Cryan, R.A., Unwin, Rodney T., Massarella, Alistair J., Sibley, Martin J.N. and Garrett, Ian (1992) A comparison of coherent digital PPM with PCM. European Transactions on Telecommunications, 3 (4). pp. 331-340. ISSN 1124-318X

Digital pulse position modulation (PPM) is a preferred modulation format for the ideal photon counting channel and optical intersateilite links. Here we examine its potential for the coherent optical fibre communications channel. We present a thorough performance and optimisation analysis. Comparisons, at a wavelength of 1.5 m, are made with shot-noise limited coherent PCM (homodyne and heterodyne ASK, FSK and PSK) over a range of fibre band-widths and varying PPM word size. We conclude that for moderate to high fibre bandwidths homodyne digital PPM should achieve an improvement in sensitivity of typically 5 dB over homo-dyne PSK PCM

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