Enhancing BPSK and OOK modulations using hybrid 2BPSK-OOK technique for optical fiber communications systems

A hybrid 2 slots binary phase shift keying-on off keying (hybrid 2BPSK-OOK) scheme is proposed as a new modulation technique to improve the performance of both conventional binary phase shift keying (BPSK) and on-off (OOK) modulation techniques in optical fiber communications systems. In conventional BPSK scheme, a consecutive stream of low power BPSK symbols are transmitted, while in the proposed scheme, a less number of high power BPSK symbols are transmitted in a two slot 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 optimal decoding for the proposed scheme are all studied in this paper. An upper bound on the bit-error rate is obtained for the proposed scheme and is compared to that of the traditional schemes under the same energy per bit constraint. Our results reveal that, for both moderate and high signal-to-noise ratios, the proposed hybrid scheme achieves much lower levels of bit-error rates than that of ordinary coherent- and direct-detected OOK schemes. However, at all energy per bit levels, the proposed scheme achieves less performance than that of ordinary BPSK. In addition, the proposed modulation scheme achieves much higher bandwidth-utilization efficiencies as compared to that of ordinary schemes.