Design of cellular backhaul topology using the FSO technology

The increasing number of mobile devices and high-speed services accelerate the growth of traffic in cellular backhaul networks. The traditional technologies used in the backhaul, copper, radio links and optical fibers, either cannot offer high data-rate, or are expensive. In this paper, we propose mixed integer programming models to facilitate upgrading the cellular backhaul using the free space optical (FSO) technology, a cost-effective and high-bandwidth solution. Since the optical signal is transmitted along line-of-sight and FSO links are sensitive to weather conditions, we incorporate mirrors in the models to provide alternative paths for pairs of FSO nodes without line-of-sight, and increase the path diversity to enhance the resilience. Optical fibers existing in the backhaul are considered in the models and reused to decrease the upgrading cost and improve reliability. The presented models can deliver topologies for various requirements on cost and resilience. They can also be used to develop topology planning and optimization tools.