PAM-SCFDE for Optical Wireless Communications

Multipath dispersion is a serious challenge in visible light communication (VLC) systems as these systems are used for indoor applications where there can be many reflections of the transmitted signal from the ceiling, walls, equipment, etc. These reflected signals cause intersymbol interference in the receiver and can degrade the performance of the system considerably. Orthogonal frequency-division multiplexing (OFDM) for optical wireless communications was introduced to mitigate multipath dispersion and has been well investigated in the literature. Recently, single-carrier systems with frequency-domain equalization (SCFDE) have been proposed as alternatives to OFDM. In this paper, we present pulse amplitude modulated SCFDE (PAM-SCFDE) to mitigate multipath dispersion in VLC systems. We also compare the proposed PAM-SCFDE with existing OFDM and SCFDE techniques for optical wireless communications in terms of analytical and simulated bit-error-rate (BER) performance, power-spectral efficiency, peak-to-average power ratio (PAPR), and overall system complexity. The proposed PAM-SCFDE requires lower per bit signal-to-noise ratio to achieve a BER of 10^-4 or smaller for modulation sizes common in practice, both with and without considering the effects of light-emitting diode transmitters, such as nonlinearity, forward current restriction, and bandwidth limitation. Furthermore, it exhibits better power efficiency for data rates less than 3 bit/s/Hz, lower PAPR and system complexity compared to other systems.