Hybrid optical/RF backhauling for 5G networks

Backhaul technologies include traditional technologies such as Radio Frequency (RF) or Optical Fibers (OF) backhauls and include new technologies such as Free Space Optical (FSO) or hybrid RF/FSO backhauls. This paper aims to improve the network connectivity by adding a limited number of OF links along with the wireless connections of RF, FSO or hybrid RF/FSO backhaul links between the small cells. The connectivity is improved while satisfying the minimum data rate (R) constraint and taking into consideration the cost and reliability of different links. We address the problem of maximizing the algebraic connectivity due to inserting different types of backhaul technologies. The Fiedler value, which is the algebraic connectivity of a graph, is used to measure the connectivity of the network. We show that under realistic cost assumption and linear relaxation, the problem is a convex optimization problem. Simulation results show that, using the proposed solution, a high connectivity can be achieved.