Analysis of hybrid FSO/RF communication system under the effects of combined atmospheric fading and pointing errors

Although free space optical communication (FSO) has attracted overwhelming interest in research and implementations due to lots of advantages it provides, it is limited to short link span due to adverse atmospheric and weather conditions. Among the different strategies adopted by researchers to improve FSO link reliability, its combination with radio frequency (RF) link to form hybrid FSO/RF links has been another promising mitigation strategy against atmospheric turbulence and weather induced loses. Therefore in this paper, the performance analysis of a hybrid FSO/RF communication link is analyzed. The RF link follows the Rice distribution with 16 quadrature amplitude modulation, while the FSO link follows the Malaga distribution with multi-pulse position modulation scheme. Novel expressions for the outage probability and bit error rate (BER) are derived for the RF, FSO and hybrid FSO/RF system. These were later used to analyze the performance of the hybrid system in moderate and strong atmospheric turbulence conditions. The results indicated that regardless of the severity of atmospheric turbulence, lower values of the normalized jitter standard deviation lead to better outage probability performance. The use of the hybrid FSO/RF link reduces the outage probability from being of the order of 10(-2) of the FSO link alone to being of the order of 10(-5). Furthermore, after investigating and comparing the behavior of the BER of the FSO and combined FSO/RF communication link, it was observed that in the low signal to noise ratio (SNR) region, the hybrid FSO/RF link performs better that the FSO alone. However, as the average SNR is increased, the BER of the hybrid FSO/RF link increases till it merges with that of the FSO alone. Thus in the high SNR region, the FSO link alone performs better than the hybrid link. This proves the effectiveness of employing the hybrid RF/FSO system.