Optimizing User Association and Spectrum Allocation in HetNets: A Utility Perspective

TL;DR

This paper analyzes and optimizes user association and spectrum allocation in multi-tier HetNets using stochastic geometry, deriving analytical solutions for utility maximization in both uplink and downlink scenarios.

Contribution

It provides the first analytical framework for jointly optimizing user association biases and spectrum partition ratios in HetNets based on utility maximization.

Findings

Optimal user association biases are derived analytically.

Spectrum partitioning favors downlink utility, while spectrum sharing benefits uplink with power control.

Uplink and downlink associations need not be symmetric.

Abstract

The joint user association and spectrum allocation problem is studied for multi-tier heterogeneous networks (HetNets) in both downlink and uplink in the interference-limited regime. Users are associated with base-stations (BSs) based on the biased downlink received power. Spectrum is either shared or orthogonally partitioned among the tiers. This paper models the placement of BSs in different tiers as spatial point processes and adopts stochastic geometry to derive the theoretical mean proportionally fair utility of the network based on the coverage rate. By formulating and solving the network utility maximization problem, the optimal user association bias factors and spectrum partition ratios are analytically obtained for the multi-tier network. The resulting analysis reveals that the downlink and uplink user associations do not have to be symmetric. For uplink under spectrum sharing, if all tiers have the same target signal-to-interference ratio (SIR), distance-based user association is shown to be optimal under a variety of path loss and power control settings. For both downlink and uplink, under orthogonal spectrum partition, it is shown that the optimal proportion of spectrum allocated to each tier should match the proportion of users associated with that tier. Simulations validate the analytical results. Under typical system parameters, simulation results suggest that spectrum partition performs better for downlink in terms of utility, while spectrum sharing performs better for uplink with power control.