Interference analysis and MUI-cancellation in DCO-OFDMA-based IM/DD systems for VLC

Abstract

The arresting virtue of Visible Light Communication (VLC) to expedite illumination and communication contemporaneously by exploiting sustainable and energy-efficient illuminating devices like Light Emitting Diodes (LEDs) in an indoor environment, enables it to resemble like a small scale cellular communication network providing data access to multiple users within its vicinity. This emphasizes to assure efficacious synchronization between the transmitter and receiver. Consequently, there is an urge to address the synchronization aspects in optical orthogonal frequency division multiple access (OOFDMA) reconcilable with Intensity Modulated (IM)/Direct Detection (DD) systems for VLC. Moreover, in an uplink scenario the existence of frequency offsets (FO) which emanates due to the existence of Doppler shift and symbol time offset (STO) leads to interference among the users as well induces to interfere with the desired user leading to most detrimental aspect called multiuser interference (MUI). This paper derives the analytical expressions for the deterioration of signal to interference noise ratio (SINR) in DC-Biased optical-OFDMA (DCO-OFDMA) system in view of the existence of STO. Furthermore, a modified version of single user detection (SUD) scheme and certain modified versions of synchronization algorithms to mitigate the effects of STO are illustrated for DCO-OFDMA flexible to be implemented for VLC Networks. In addition, Cramer Rao Lower Bound (CRLB) is derived for FO and STO estimators using joint parameter estimation for the uplink scenario and is verified through simulations.