Buffer-Aided Max-Link Relaying for Free Space Optical Communication With Delay Constraints

In this paper, we introduce the concept of buffer-aided cooperative relaying for a free-space optical (FSO) communication system. The proposed FSO system consists of $K$ decode-and-forward(DF) relays, each equipped with a buffer of size $L$. The proposed system undergoes both path loss and atmospheric turbulence (AT) induced fading, and to evaluate the system performance a weak, as well as strong AT region is considered. The Markov chain (MC) approach is used to derive the state transition matrix of the system, which is then further used to model the evolution of buffer states. Analytical expressions of the outage probability and average bit error rate (ABER) are obtained with the help of state transition matrix. The average packet delay of the system is also evaluated with the help of obtained outage probability. The performance of the considered system is analyzed for different values of $K$ and $L$. The performance is then further compared with the non-buffer-aided (NBA) cooperative relaying for FSO communication systems and it has been observed that the proposed buffer-aided FSO system significantly outperforms the NBA FSO systems for entire range of turbulence. Finally, the impact of $L$ and $K$ on the average packet delay of the system is examined.