The Use of Diversity Antennas in High-Speed Wireless Systems: Capacity Gains, Fairness Issues, Multi-User Scheduling

The Use of Diversity Antennas in High-Speed Wireless Systems: Capacity Gains, Fairness Issues, Multi-User Scheduling

Sem Borst Phil Whiting

Abstract: The use of antenna arrays provides a natural mechanism for enhancing spectral efficiency so as to improve data rates, capacity or coverage. There are various approaches for operating antenna-array system, with diversity schemes belonging to the simpler ones to deploy. In the present paper, we specifically examine the capacity improvements from diversity antennas in multi-user scenarios. Although available single-user results yield valuable insight for voice communications, they do not directly translate to multi-user data systems.

First of all, we show that the use of diversity antennas has the effect of dampening the variations in the channel conditions, This reduces the scope for channel-aware scheduling mechanisms such as HDR to obtain capacity gains by exploiting fluctuations in the feasible transmission rates. Conversely, in he presence of scheduling, diversity antennas may produce substantially smaller gains or even have a negative impact on capacity.

Second, in heterogeneous scenarios, we find that the capacity improvements from diversity antennas may widely vary, depending on what fairness notion is adopted. If the proportion of time slots is used as fairness criterion, then the gains in total throughput tend to be significant, but the edge users only receive a marginal share. In case the fairness measure is defined in terms of throughput ratios, then the gains tend to be limited population-wide.

Status: Bell Laboratories Technical Memorandum, 2001.

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Bert Hochwald<hochwald@lucent.com>