On the Performance of RF-FSO Links with and without Hybrid ARQ
  This paper studies the performance of hybrid radio-frequency (RF) and free-space optical (FSO) links assuming perfect channel state information (CSI) at the receiver. Considering the cases with and without hybrid automatic repeat request (HARQ), we derive closed-form expressions for the message decoding probabilities as well as the throughput and the outage probability of the RF-FSO setups. We also evaluate the effect of adaptive power allocation and different channel conditions on the throughput and the outage probability. The results show the efficiency of the RF-FSO links in different conditions. 
Behrooz Makki, Tommy Svensson, Thomas Eriksson, Mohamed-Slim Alouini
cs.IT math.IT