Double relay selection for combating the impact of interference and hardware impairments in mixed RF/FSO two way relay networks

In this paper, investigation of mixed radio frequency (RF)/ free space optical (FSO) decode and forward (DF) two way relaying (TWR) has been performed. It has been assumed that the relay hardwares involved are prone to aggregated hardware impairments and operate near the vicinity of multiple co-channel interferers (CCIs). In order to combat the impact of hardware impairment and interference, double relay selection scheme has been employed in the system model. Therefore, the cooperation between the RF and FSO source nodes takes place in two different paths to establish TWR. The fading characteristics of the RF and CCI links have been modeled using the Rayleigh distribution. The atmospheric turbulence on the FSO link has been assumed to undergo Malaga irradiance model. For the considered system, analysis of outage probability has been performed. In fact, the closed-form for the outage probability has been derived in terms of Meijer-G function. The derived expressions are then approximated for the high signal to noise ratio (SNR) by exploiting the asymptotic analysis of outage probability. Results are present to confirm that the reliability of the communication channel is impacted by number of nodes available for selection, type of optical demodulation, atmospheric turbulence, pointing error, interference and hardware impairment. The analytical results are confirmed using the Monte-Carlo simulations.