Hybrid BPSK-modified MPPM: A scheme for enhancing optical MPPM in optical fiber communications

A hybrid binary phase shift keying-modified multipulse pulse-position modulation (hybrid BPSK-modified MPPM) scheme is proposed as a new modulation technique to improve both the symbol-error rate performance and bandwidth utilization efficiency of conventional optical multi-pulse pulse position modulation (MPPM) scheme in optical fiber communication systems. Whereas in conventional MPPM scheme, unmodulated pulses are transmitted in every signal block, BPSK modulated pulses is transmitted in the proposed hybrid scheme. That is, the information is encoded in both the positions and phases of the transmitted pulses. The transmission characteristics, transmitter and receiver structures, bandwidth utilization, and optimum decoding for the proposed scheme are presented in this paper. Several performance measures are derived and compared to those of conventional MPPM schemes, adopting both coherent and direct detection receivers, under the same data transmission rates. Our results reveal that, at same average power levels, the proposed hybrid BPSK-modified MPPM scheme achieves much lower levels of symbol-error rates compared to those of ordinary MPPM schemes. Furthermore, in terms of bandwidth-utilization efficiency, the proposed hybrid modulation scheme achieves much higher efficiencies than that of ordinary MPPM schemes.