Agile, Resilient and Cost-efficient Mobile Backhaul Networks

University dissertation from KTH Royal Institute of Technology

Abstract: The exponentially increasing traffic demand for mobile services requires innovative solutions in both access and backhaul segments of 5th generation (5G) mobile networks. Heterogeneous networks (HetNets), which use low-cost small cells for capacity upgrade while ensuring network coverage by macro cells, are a promising solution for the wireless access. However, the backhaul segment has received considerably less attention and still falls short in meeting the stringent requirements of 5G in terms of capacity and availability.HetNets together with mobility requirements motivate the use of microwave backhauling that supports fiber-like capacity with millimeter-wave communications. However, these carrier frequencies are subject to weather disturbances like rain that may substantially degrade the network throughput and availability performance. We develop a fast and accurate rain detection algorithm that triggers a network-layer strategy, e.g., rerouting, to mitigate its effects. The evaluation results show that with small detection error the network throughput increases while posing low overhead on the network.The rain impact can be alleviated by regular rerouting using a centralized approach realized by a software defined network (SDN). However, careless reconfiguration may impose inconsistency due to asynchrony between different switches, which leads to a significant temporary congestion and limits the gain of rerouting. We propose a consistency-aware rerouting framework by considering the cost of reconfiguration. At each time, the centralized controller (CC) may either take a rerouting decision to increase the network throughput while accepting the switching cost, or choose the no-rerouting decision at the expense of a decreased throughput, due to route sub-optimality. We use a predictive control algorithm to provide an online sequence of decision policies to minimize the total data loss. Compared to the regular rerouting, our proposed approach reduces the throughput loss and substantially decreases the number of reconfigurations by wisely selecting the time to reroute the traffic.In the thesis we also study which backhaul options is the best from a techno-economic perspective. Fiber solutions provide high data rates with robust connectivity under different weather conditions, whereas wireless solutions offer high mobility at low installation costs with lower data rate and availability. We develop a comprehensive framework to calculate the total cost of ownership of the backhaul segment and analyze the profitability in terms of cash flow and net present value. The evaluation results highlight the importance of selecting proper backhaul solution to increase profitability.In summary, this thesis aims to provide guidelines for efficient backhaul solutions for future mobile networks in terms of throughput and availability. The results reveal that microwave backhauling may experience long lasting link degradation due to rain, which necessitates intelligent rerouting approaches. It is also shown that fiber is the most promising option in terms of minimum cost and highest profitability for ultra-dense networks. Given that the standardization of 5G mobile networks has not started yet, the results of this thesis may provide fundamental design guidelines for those standards.