Optimal Hierarchical Radio Resource Management for HetNets with Flexible Backhaul

Heterogeneous networks (HetNets) have been considered as a promising architecture for upcoming 5G networks due to their high energy and spectrum efficiency. However, providing backhaul connectivity for all macro and pico base stations (BSs) in HetNets constitutes a significant share of infrastructure cost. Recently, the idea of flexible backhaul has drown a lot of attention both from industry and academia. Under this architecture, not all the pico BSs are connected to the backhaul, resulting in a significant reduction in the infrastructure costs. In this regard, pico BSs without backhaul connectivity need to communicate with their nearby BSs in order to have indirect accessibility to the backhaul. This makes the radio resource management (RRM) in such networks more complex and challenging. In this paper, we address the problem of cross-layer RRM in HetNets with flexible backhaul. We formulate the RRM problem as a two timescale non-convex stochastic optimization problem which jointly optimizes flow control, routing control, interference mitigation and link scheduling in order to maximize a generic network utility. By exploiting the hidden convexity of this non-convex problem, we propose an iterative algorithm which is converges to the global optimal solution. The proposed solution has low complexity and requires low signalling and message passing among different nodes, which makes it scalable. Moreover, due to the proposed two-timescale design, it is robust to the backhaul signalling latency as well. Simulation results demonstrate the significant performance gain of the proposed solution over various baselines.