Proposal of a hybrid QAM-MPPM technique for optical communications systems

M-ary quadrature amplitude modulation (QAM) is a class of non-constant envelope scheme that can achieve high bandwidth efficiency under an average signal power constraint. In this paper, a hybrid M-ary quadrature amplitude modulation multi-pulse pulse-position modulation (hybrid QAM-MPPM) technique is proposed for optical communications systems. Both transmitter and receiver block diagrams, which utilize intensity modulation/direct detection (IM/DD) scheme, are introduced. The proposed system is analyzed theoretically and its bit-error rate (BER) performance is derived and investigated. Our results reveal that, under the conditions of fixed data rates, bandwidth, and energy per bit, the proposed technique outperforms both traditional QAM and MPPM sub-carrier modulation techniques.