A PAM-PPM signalling format in optical fibre digital communications

A combined pulse amplitude modulation (PAM) and pulse position modulation (PPM) technique is proposed and investigated as a feasible solution of the problem of line encoding in optical fibre communication systems. The basic idea is that of exploiting PAM and PPM jointly, to give rise to three different waveforms in one signalling period, without resorting to more than two signal levels. Some evaluations of the behaviour of this signalling format are reported in terms of coding efficiency, spectral density, timing information, and error probability. Alternative receiving schemes are also devised to improve system performance.