Performance analysis of downlink multipath multi-user NOMA-VLC system

Abstract

In the present paper, we have investigated performance of Non-Orthogonal Multiple Access based downlink multipath multi-user Visible Light Communication System. The Bit Error Rate (BER), sum rate and outage probability have been simulated using Line-Of-Sight (LOS) and LOS plus first reflection (L-R1) signal for two-user and three-user system. The simulation has been carried out for different values of semi-angle \({\mathrm{\varphi }}_{1/2}\) of the LED i.e. \(30^\circ , 50^\circ\) and 70\(^\circ\). In the two-user system, the LOS simulation result shows that the error probability is 7.49 × 10−3, 4.88 × 10−3 and 1.03 × 10−1 when \({\mathrm{\varphi }}_{1/2}\) equals to70\(^\circ\), 50° and \(30^\circ\) respectively for user-1. And for user-2, the BER is found to be 4.89 × 10−2, 5.84 × 10−2 and 3.73 × 10−1 using \({\mathrm{\varphi }}_{1/2}\) equals to70\(^\circ\), \(50^\circ\) and \(30^\circ\). Thus, the optimal semi-angle \({\mathrm{\varphi }}_{1/2}\) for user-1 and user-2 using LOS signal is \(50^\circ\), 70\(^\circ\) respectively. However, for the three-user system, the error probability increases when compared to two-user system and the optimal values of semi-angle for user-1 changes to \(30^\circ\) and for user-2 & user-3, it is 70\(^\circ\). Moreover, in two-user system with L-R1 signal, the optimal value is 70\(^\circ\) for both user-1 and user-2. The SIC method fails to decode the user’s signal when number of users increases to three in L-R1 signal case. Further, with the far user power allocation coefficient equal to 0.8, the average BER is found to be minimum for two-user system. The sum rate vs. normalized offset has been simulated for different values of semi-angle of the LED. The investigation shows that the maximum sum rate of 278.84 Mbps is achieved at \({\mathrm{\varphi }}_{1/2}\) equals to \(50^\circ\) for the two-user system using LOS signal. We have also examined the effect of shadowing (blocked LOS signal) and found that sum rate is almost zero for small values of \({\varphi }_{1/2}\) i.e. \(20^\circ\) and \(30^\circ\). Finally, for the semi-angle value of \(30^\circ\) the outage probability (for target rate beyond 3bps/Hz) reaches to 100 percent for both users.