Multi-User Provisioning in Millimeter-Wave Urban Cellular Networks

TL;DR

This study evaluates multi-user capacity in millimeter-wave urban cellular networks, comparing TDMA and SDMA, and proposes algorithms to optimize network performance considering realistic antenna patterns and interference effects.

Contribution

It introduces a comprehensive analysis of multi-user mm-wave networks using ray-tracing data, and develops a heuristic for link allocation to improve capacity estimation.

Findings

SDMA outperforms TDMA in throughput, up to 2 Gbps with 8x8 arrays.

Inter-cell interference is negligible, limiting TDMA performance.

Larger antenna arrays reduce intra-cell interference and lower costs.

Abstract

In this paper we present the first comprehensive study of the multi-user capacity of millimeter-wave (mm-wave) urban cellular networks, using site-specific ray-tracing propagation data and realistic antenna array patterns. We compare the performance of TDMA and SDMA (time and spatial division multiple access, respectively) for diverse network scenarios and antenna configurations. We propose a greedy heuristic algorithm to solve the network-wide directional link allocation problem, thereby estimating the achievable capacity and coverage of multi-user mm-wave networks. Our results show that inter-cell interference is negligible, so that TDMA performance is strictly limited by air-time sharing. By contrast, the major limiting factor for SDMA is intra-cell interference, emphasizing the impact of real antenna array sidelobes. Nonetheless, SDMA significantly outperforms TDMA in terms of average UE throughput, by up to 2 Gbps using 8x8 arrays. As an important design insight, our results show that larger base station antenna arrays limit intra-cell interference while compensating for small UE arrays, reducing costs and beamforming requirements in practical SDMA networks. Our analysis also shows that the limited number of antenna sub-arrays in a practical hybrid beamforming architecture may force SDMA to drop UEs with good coverage, highlighting a tradeoff between base station densification and antenna resources.