Limitation of SDMA in Ultra-Dense Small Cell Networks

Abstract

Benefitting from multi-user gain brought by multiantenna 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 ultradense 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.

A Comprehensive Survey on Millimeter Wave Communications for Fifth-Generation Wireless Networks: Feasibility and Challenges

“…Nevertheless, both have their benefits and drawbacks, and it is nontrivial to obtain a hybrid design that balances both. Taking advantage from multi-user gain induced by massive MIMO techniques [294], SDMA is capable of significantly improving spatial throughput in mmWave communications for 5G networks. Specifically, SDMA simultaneously serves multiple UEs in the same channel over identical spectrum resources by the superposition of the beam (i.e., it divide the space into a number of orthogonal spatial beams) [294].…”

“…Taking advantage from multi-user gain induced by massive MIMO techniques [294], SDMA is capable of significantly improving spatial throughput in mmWave communications for 5G networks. Specifically, SDMA simultaneously serves multiple UEs in the same channel over identical spectrum resources by the superposition of the beam (i.e., it divide the space into a number of orthogonal spatial beams) [294]. In [295], a low complexity joint transmission scheme for mmWave massive MU-MIMO system is introduced, combining SDMA and interference suppression precoding to improve system sum-rate capacity.…”

Indexed Multiple Access with Reconfigurable Intelligent Surfaces: The Reflection Tuning Potential

“…SDMA: SDMA is implemented in MIMO systems that utilize uncorrelated channels as another DoF, allowing multiple simultaneous transmissions over the same time-frequency resource [3], [8]. Nevertheless, the benefit comes at the cost of rigorous channel estimation and precoding.…”