Backhaul-Aware Optimal Access Selection for Traffic Offloading in Small-Cell Networks

The limited backhaul capacity has been considered as an important issue that influences the performance of traffic offloading in small-cell networks. We thus investigate how mobile users (MUs) efficiently offload traffic to different small cells with the new paradigm of dual-connectivity, subject to different backhaul capacities of small cells. Specifically, we formulate an optimization problem that jointly optimizes the MUs' access-selections, traffic scheduling, and transmitpower allocations, with the objective of minimizing all MUs' mobile data cost. To tackle with the difficulty due to the mixed binary nonconvex optimization problem, we decompose the joint optimization problem into a subproblem that optimizes the MUs' traffic scheduling and power allocations and a top problem that optimizes the MUs' access-selections. Based on our previous study [1], we can efficiently solve the subproblem by exploiting its hidden monotonicity. With the solution of the subproblem, we further propose two effective algorithms (namely, a simulated annealing based algorithm and a fast access-selection algorithm) to solve the top problem. The key idea of the fast access-selection algorithm is to exploit the information of limited backhaul capacities and properly remove the infeasible selection to reduce the search space. Numerical results validate the effectiveness of our proposed algorithms and the performance advantage of the proposed joint resource allocations for traffic offloading.