Proposal and Performance Evaluation of a Hybrid BPSK-Modified MPPM Technique for Optical Fiber Communications Systems

A hybrid binary phase shift keying-modified multi-pulse pulse position modulation (hybrid BPSK-modified MPPM) scheme is proposed as a new modulation technique to improve the performance of both conventional binary phase shift keying (BPSK) and multi-pulse pulse position modulation (MPPM) techniques in optical fiber communications systems. In conventional BPSK scheme, a consecutive stream of low power BPSK symbols are transmitted. However, in the proposed scheme, a less number of high power BPSK symbols are transmitted in a hybrid frame and their positions are exploited to transmit more bits. That is, the transmitted information is carried in both the positions and phases of the transmitted pulses. The transmission characteristics, transmitter and receiver block diagram, bandwidth-utilization, and optimum decoding process for the proposed scheme are all studied in this paper. Several performance measures are also derived and compared to those of conventional schemes in optical fiber channels. Our results reveal that, under an average power constraint, the proposed hybrid BPSK-modified MPPM scheme achieves much lower levels of bit-error rates and symbol-error rates than those of ordinary BPSK and ordinary MPPM schemes, respectively, for both moderate or high signal-to-noise ratios. In addition, the proposed modulation scheme achieves much higher bandwidth-utilization efficiencies than those of ordinary schemes.