A Cross-Tier Scheduling Scheme for Multi-Tier Millimeter Wave Wireless Networks

Due to abundant frequency resources, millimeter wave (mm-wave) spectrum has drawn much attention as a solution to bandwidth scarcity. However, many characteristics of mm-wave transmissions, such as blockage and reduced coverage, make conventional network architectures very inefficient for use in mm-wave networks. A recently proposed multi-tier mm-wave network architecture allows for relaying around blockages and enlarges the coverage of each base station at an acceptable deployment cost. Nevertheless, this architecture introduces major challenges to the scheduling of each tier. The necessity of both enabling flexible user association and fully exploiting the wireless backhaul requires a cross-tier consideration of the multi-tier mm-wave network. We comprehensively analyze the scheduling problem of a downlink multi-tier mm-wave network by jointly regulating the transmissions in all tiers. The cross-tier optimization problem is NP-hard, but a sub-optimal scheme which iteratively optimizes the schedule in different tiers of the network is proposed with polynomial computational complexity. Simulation results show that our algorithm significantly outperforms the benchmarks in both spectral efficiency and fairness with various user distributions.