HARQ Performance over FSO Channels with Atmospheric Fading and Pointing Errors

Free space optical communications (FSO) have witnessed a growing interest in the last few decades due to its various advantages. However, this technology suffers from its sensitivity to the atmospheric conditions such as fog, dust storms, and high temperature, etc. In order to overcome these issues, many techniques have been proposed in literature. In this paper, we study the effectiveness of using hybrid automatic re-transmissions request (HARQ) technique to overcome FSO channels impairments. Two HARQ protocols are considered: ALOHA (ALO) and incremental redundancy (IR). For each protocol, we derive the outage probability expressions, throughput and the average number of the re-transmissions. In addition, we study the HARQ performance in terms of delay and packet sojourn. The results show the effectiveness of using HARQ-IR over ALO protocol.