Performance Analysis and Optimization of Wireless Heterogeneous Networks

Performance Analysis and Optimization of Wireless Heterogeneous Networks Yicheng Lin Doctor of Philosophy Graduate Department of Electrical and Computer Engineering University of Toronto 2015 Heterogeneity is becoming a key characteristic of future generations of wireless cellular networks. By deploying different low-power access points in addition to the traditional macro base-stations (BSs), various types of heterogeneous networks (HetNets) can be formed to improve the coverage and transmission rate. Through developing efficient algorithms, analyzing performance and optimizing systems design parameters, this thesis studies three representative HetNet architectures, namely shared relays, multi-tier HetNets, and distributed antenna systems (DAS). Relays utilize an in-band backhaul and have low deployment cost. The first part of the thesis studies a sectorized cellular system with relays and, in particular, focuses on a novel architecture in which each relay is shared by M adjacent cells. We develop a joint user scheduling, resource allocation and beamforming algorithm for shared relaying to maximize the proportionally fair utility, taking into account practical in-band backhaul constraints. The benefit of shared relaying in terms of rate and utility is shown in a system-level simulation. The use of shared wireless medium for the backhaul of relays induces half-duplex loss in relay system, which fundamentally limits the performance gain. Motivated by this fact, the second part of this thesis studies multi-tier HetNets with dedicated wired backhaul. Considering random deployment of BSs, we derive the closed-form mean proportionally fair utility of multi-tier HetNets in both downlink and uplink. The optimal user association and spectrum allocation schemes are obtained by optimizing this utility, and are validated with simulations. In a multi-tier HetNet, BSs typically transmit independently. The third part of the thesis studies a DAS in which distributed antennas are connected via wired backhaul to the central controller and can cooperatively transmit to users. This thesis analyzes the downlink spectral efficiency of DAS where antennas are randomly deployed. We show that for a regular DAS with fixed cell boundaries, selective transmission outperforms blanket transmission in most cases, and the cell-edge spectral efficiency under blanked transmission is upper bounded by a constant. Accounting for random user distribution, the user-centric DAS layout, where no explicit cell boundaries exist, is also analyzed, which is shown to outperform the regular DAS from a network perspective.