Effect of Phase Noise on the Performance of Coherent Visible Light Communication Systems

Visible light communication (VLC) builds upon the dual use of illumination infrastructure for wireless access. The recent commercialization of laser diode (LD)–empowered white light luminaires gives the opportunity to build coherent VLC systems. Coherent VLC systems can leverage the high bandwidth of lasers and advanced digital signal processing techniques to significantly improve the data rates. For coherent reception, a local oscillator in the form of a monochromatic laser is used. In practice, lasers suffer from random fluctuations in phase due to spontaneous emission and carrier density fluctuations. In this paper, we analyze the effects of phase noise on the performance of a coherent VLC system in the presence of atmospheric turbulence as encountered in outdoor and vehicular applications. We assume that a phase locked loop (PLL) is used for phase recovery. Turbulence-induced fading phase is estimated through pilot symbols and provided as input to the PLL. The PLL uses this estimated channel phase to initialize its phase estimate at the beginning of each frame. Based on the statistical distribution of the residual phase, we derive an approximate closed-form expression for the pairwise error probability (PEP) which is then used to obtain a union bound on the error rate. Through comprehensive simulations, we validate the accuracy of the derived expression and quantify the impact of phase noise on the error rate performance.