Cell Selection for Joint Optimization of the Radio Access and Backhaul in Heterogeneous Cellular Networks

This chapter considers heterogeneous cellular networks where clusters of small cells are locally deployed to create hotspot regions inside the macro‐cell area. Most of the research on this topic has focused on mitigating co‐channel interference; however, wireless backhaul has recently emerged as an urgent challenge to enable ubiquitous broadband wireless services at small cells. In realistic scenarios, the backhaul may constrain the amount of signalling that can be exchanged amongst neighbouring cells, which aim to coordinate their operations in real time; furthermore, in highly loaded cells (such as hotspots), the backhaul can limit the data rate experienced by end users. Here, we develop a novel cell‐association framework, which balances users amongst heterogeneous cells to improve the overall radio and backhaul resource usage and increase the system performance. We describe relationships between cell load, resource management and backhaul capacity constraints. Then, we model the cell‐selection problem as a combinatorial optimization problem and we present two heuristic algorithms, named Evolve and Relax, to solve it with limited complexity. Our analysis shows that the Evolve algorithm converges to a near‐optimal solution, leading to notable improvements with respect to the classic SINR‐based association scheme in terms of throughput and resource utilization efficiency.