Downlink MIMO HetNets: Modeling, Ordering Results and Performance Analysis

TL;DR

This paper develops a comprehensive model for downlink multi-antenna HetNets, providing ordering results, bounds, and performance comparisons for different transmission schemes, revealing insights into antenna deployment and scheme efficiency.

Contribution

It introduces a unified analytical framework with ordering results and bounds for various multi-antenna transmission techniques in HetNets, enhancing understanding of their relative performance.

Findings

Spreading antennas across many single-antenna BSs is preferable to fewer multi-antenna BSs.

SU-BF yields higher coverage and per-user rate than SDMA.

SDMA can outperform in area spectral efficiency under certain conditions.

Abstract

We develop a general downlink model for multi-antenna heterogeneous cellular networks (HetNets), where base stations (BSs) across tiers may differ in terms of transmit power, target signal-to-interference-ratio (SIR), deployment density, number of transmit antennas and the type of multi-antenna transmission. In particular, we consider and compare space division multiple access (SDMA), single user beamforming (SU-BF), and baseline single-input single-output (SISO) transmission. For this general model, the main contributions are: (i) ordering results for both coverage probability and per user rate in closed form for any BS distribution for the three considered techniques, using novel tools from stochastic orders, (ii) upper bounds on the coverage probability assuming a Poisson BS distribution, and (iii) a comparison of the area spectral efficiency (ASE). The analysis concretely demonstrates, for example, that for a given total number of transmit antennas in the network, it is preferable to spread them across many single-antenna BSs vs. fewer multi-antenna BSs. Another observation is that SU-BF provides higher coverage and per user data rate than SDMA, but SDMA is in some cases better in terms of ASE.