Multihop RIS-Assisted FSO-RF System Over Double Generalized Gamma Fading

Reconfigurable intelligent surface (RIS) is a promising technology to avoid signal blockage by creating virtual line-of-sight (LOS) connectivity for free-space optical (FSO) and radio frequency (RF) wireless systems. This paper considers a mixed FSO-RF system by employing multiple RISs in both the links for multihop transmissions to extend the communication range. We develop probability density function (PDF) and cumulative density function (CDF) of the signal-to-noise ratio (SNR) for the cascaded channels by considering double generalized gamma (dGG) turbulence with pointing errors for the FSO link and the dGG distribution to model the signal fading for the RF. We derive exact closed-form expressions of the outage probability, average bit-error-rate (BER), and ergodic capacity using the decode-and-forward (DF) relaying for the mixed system. We also present asymptotic analysis on the performance in the high SNR regime depicting the impact of channel parameters on the diversity order of the system. We use computer simulations to demonstrate the effect of system and channel parameters on the RIS-aided multihop transmissions.