Polar Coordinate Based Modulation: Concept, Performance Analysis and System Design

In this paper, a nonlinear base-band modulation scheme, namely POLar COordinate based Modulation (POLCOM), is proposed for intensity modulation with direct detection (IM/DD) based optical wireless communication (OWC) systems. Two detectors including the optimal maximum likelihood detector (MLD) operated in polar coordinate and the joint detector (JD) operated in rectangular coordinate are investigated. Over additive white Gaussian noise (AWGN) channels, the symbol error rate (SER) performances of POLCOM using these two detectors are derived in high signal-to-noise ratio (SNR) regime. To achieve good performance in terms of SER, a heuristic greedy walk algorithm (GWA) is proposed to design the signal constellations for POLCOM. Comprehensive comparisons are made with existing schemes under the same signal bandwidth and spectral efficiency. Through fair comparisons, it is shown that the proposed POLCOM outperforms most of existing schemes.