Comparison of link selection algorithms for free space optics/radio frequency hybrid network

The great potential of free space optics (FSO) communication motivates to use it for future requirement of high bandwidth links. However, the widespread use of this technology has been hampered by the reduced availability because of weather effects. To overcome these shortcomings a back-up link can be used so that the combined hybrid network may achieve carrier class availability. A hybrid, FSO/wireless LAN (WLAN) self-synchronising architecture is presented, which provides transparent connectivity without protocol overhead. The switching from one link to another needs efficient algorithms to achieve the optimal bandwidth utilisation while maintaining availability. Generally, the received signal strength is considered as a parameter for switching between the links. In this study, link selection has been analysed for a variety of algorithms, including filtering and hysteresis, using measured data of fog events. The combination of time and power hysteresis is found to be the optimum solution.