Analysis of multiple pulse position modulation when operating over graded-index plastic optical fibre

The author presents an original performance analysis of a multiple pulse position modulation (PPM) scheme using graded-index plastic optical fibre. The particular multiple PPM scheme considered here uses two pulses in a 12-slot frame to code six bits of PCM. The line rate of the system is twice that of the original PCM (1 Gbit/s). The detailed analysis presented here shows how the error performance is affected by various pulse detection errors when inter-symbol interference is present. The predicted sensitivity of the (12/2) multiple PPM scheme used is - 35.51 dBm when the pulse dispersion is low, and - 19.13 dBm at a bandwidth of 0.7 times the PCM data rate. It is also shown that the use of some 3-bit code-words in the multiple PPM scheme can help to reduce the effects of dispersion so that a hybrid 2/3 pulse scheme has a 3.61 dB advantage at low bandwidths.