Coverage Analysis and Resource Allocation in Heterogeneous Networks

The focus of this thesis is the analysis and design of multi-tier heterogenous networks (HetNets) with large density of access points (APs) located without a deterministic structure. We use stochastic geometry, specifically Poisson point processes (PPPs), to capture the randomness in AP locations. To differentiate their structural characteristics, APs are categorized into different tiers, each modeled by a PPP. The problem of cell association and resource allocation in a HetNet is considered from two different points of view: when the user is i) mobile and ii) stationary. To incorporate mobility in coverage analysis for mobile users, we derive the probability of handoff in an irregular multi-tier HetNet. To account for the service degradation due to handoffs, we propose a linear cost function, and use this to associate high speed users to upper tiers (e.g., macrocells) with a lower AP density. For stationary users, we first derive the statistical distribution of the load, and the minimum bandwidth required to meet an outage constraint in a multi-tier HetNet. This result is most useful for system design by relating the required spectrum to choices of network parameters. We then consider the dual problem with the objective of maximizing the overall rate coverage with orthogonal spectrum allocation across tiers given a total available bandwidth. We tackle this problem in two different phases: 1) load distribution and spectrum partitioning across tiers; 2) resource allocation across the APs and users within one tier. For analytical tractability in the former, we approximate the load of each AP by its mean, and derive the optimum tier association and fraction of spectrum to be allocated to each tier. In the latter, to account for different loads at each AP, we develop a hierarchical algorithm to allocate the available spectrum across the APs according to their load and to users according to their data rate demand. The latter benefits from adaptive power allocation and dynamic spectrum allocation across APs.Ph.D