On the performance of DF relayed hybrid RF/FSO cascaded with VLC link

This paper investigates the performance analysis of radio frequency/free space optical-visible light communication (RF/FSO-VLC) system, where a hybrid RF/FSO link is connected to an indoor VLC subsystem using decode-and-forward (DF) relay. The selection combining (SC) technique is used at the DF relay. We have considered Nakagami-m fading, Double Generalized Gamma (DGG) distributed atmospheric turbulence with Rayleigh distributed pointing errors and Lambertian pattern of the light emitting diode (LED) for the RF, FSO, and VLC links, respectively. To analyze the performance of the considered co-operative system, different performance metrics such as outage probability, bit-error-rate (BER), and ergodic capacity of the system are taken into consideration. For deriving the performance metrics, novel expressions for cumulative distribution function and probability density function of the instantaneous signal-to-noise-ratio (SNR) of hybrid RF/FSO-VLC system in terms of Meijer-G function are obtained and used. The numerical results show that the outage probability of the system is more in the strong turbulence conditions and intensity modulation/direct detection (IM/DD) technique in comparison to weak turbulence and heterodyne detection scenario. It is also seen from the results, that the BER of the system is better in case of coherent binary modulation techniques in comparison with non-coherent binary and M-ary modulation techniques. Moreover, the capacity of the system increases as the number of LEDs increase and as the height of the LEDs reduce. The asymptotic and simulation results match with the derived analytical results.