Hybrid Radio Frequency and Free Space Optical communication for 5G backhaul

Abstract

5G backhaul requires high bandwidth and hybrid Radio Frequency/ Free Space Optical (RF/FSO) Communication offers Gbps links. The weather affects availability of both mmW RF and FSO links. Below cloud ceiling, the availability of hybrid RF/FSO link is above 85.7% and it can only be used for deadline-constrained large data transfers. At 17–22km above ground, the bit error rate of FSO links reaches below 10−3 and it can be used for delay-sensitive packet transfers. In this work, first, we propose a method to determine the required number of wavelengths and storage size for large data transfers and second, we propose a distributed implementation of automatic repeat request protocol to support 10Gbps bandwidth and millisecond delay for delay-sensitive packet transfers. The simulation results show the following: With link availability of 0.85, blocking rate of 0.05 can be achieved for large data transfers, which indicates 0.05 of the cost of transferring data over 5G dmW spectrum is necessary to guarantee deadline. The distributed implementation of automatic repeat request has similar performance with selective repeat. Both theoretical and simulation results show if load exceeds 0.9 of maximum load allowed by packet error probability, delay increases about 20% drastically.