Mixed RF/FSO bidirectional system achieving spectral efficiency

The performance of two-way relay (TWR)-assisted mixed radio-frequency/free-space optical (RF/FSO) system is evaluated in this letter. The proposed system employs decode-and-forward relaying phenomena where the relay is basically an interfacing node between two source nodes \(S_1\) and \(S_2\), where \(S_1\) supports RF signal, while \(S_2\) supports FSO signal. The TWR-assisted system helps in achieving spectral efficiency by managing bidirectional communication in three time slots, thus maximizing the achievable rate of the network. The RF link is subjected to generalized \(\eta -\mu \) distribution, and the optical channel is affected by path loss, pointing errors and gamma–gamma (gg) distributed atmospheric turbulence. The novel expressions for the probability density function and cumulative distribution function of the equivalent end-to-end signal-to-noise ratio (SNR) are derived. Capitalizing on these derived statistics of end-to-end SNR, the expressions of outage probability and the bit-error rate for different binary modulations and M-ary modulations are provided.