Limitation of SDMA in Ultra-Dense Small Cell Networks

TL;DR

This paper reveals that in ultra-dense small cell networks, SDMA's spatial throughput diminishes to zero, and single-user beamforming outperforms SDMA and full SDMA in terms of throughput and critical density.

Contribution

It demonstrates the fundamental limitations of SDMA in ultra-dense networks and shows that single-user beamforming can achieve higher throughput.

Findings

SDMA throughput drops to zero in ultra-dense networks

Single-user beamforming outperforms SDMA in UDN

Critical density for optimal throughput is highest with SU-BF

Abstract

Benefitting from multi-user gain brought by multi-antenna techniques, space division multiple access (SDMA) is capable of significantly enhancing spatial throughput (ST) in wireless networks. Nevertheless, we show in this letter that, even when SDMA is applied, ST would diminish to be zero in ultra-dense networks (UDN), where small cell base stations (BSs) are fully densified. More importantly, we compare the performance of SDMA, single-user beamforming (SU-BF) (one user is served in each cell) and full SDMA (the number of served users equals the number of equipped antennas). Surprisingly, it is shown that SU-BF achieves the highest ST and critical density, beyond which ST starts to degrade, in UDN. The results in this work could shed light on the fundamental limitation of SDMA in UDN.