Design and Analysis of Bit Selections in HARQ Algorithm for Hybrid FSO/RF Channels

A novel type-II hybrid automatic repeat request (HARQ) algorithm over hybrid channels, consisting of parallel free space optical (FSO) and radio frequency (RF) links, is presented. The algorithm uses different jointly optimized puncturing and RF bit selection patterns for different retransmissions. Analytical bit error rate and throughput performance expressions for the algorithm in case of both time invariant and random fading channels for recursive systematic, non-recursive non-systematic convolutional codes and turbo codes are given. Numerical results show a gain of several dBs of the proposed algorithm when compared to HARQ that uses random bit selection for transmission through the RF channel. The performance of the algorithm for different FSO and RF link conditions is demonstrated.