Scheduling of multi-antenna broadcast systems with heterogeneous users

Krishna Jagannathan*, Sem Borst, Phil Whiting, Eytan Modiano

*Corresponding author for this work

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

We study the problem of efficiently scheduling users in a Gaussian broadcast channel with M transmit antennas and K independent receivers, each with a single antenna. We first focus on a scenario with two transmit antennas and statistically identical users, and analyze the gap between the full sum capacity and the rate that can be achieved by transmitting to a suitably selected pair of users. In particular, we consider a scheme that picks the user with the largest channel gain, and selects a second user from the next L-I strongest ones to form the best pair, taking channel orientations into account as well. We prove that the expected rate gap converges to 1/(L- 1) nats/symbol when the total number of users K tends to infinity. Allowing L to increase with K, it may be deduced that transmitting to a properly chosen pair of users is asymptotically optimal, while considerably reducing the feedback overhead and scheduling complexity. Next, we tackle the problem of maximizing a weighted sum rate in a scenario with heterogeneous user characteristics. We establish a novel upper bound for the weighted sum capacity, which we then use to show that the maximum expected weighted sum rate can be asymptotically achieved by transmitting to a suitably selected subset of at most MC users, where C denotes the number of distinct user classes. Numerical experiments indicate that the asymptotic results are remarkably accurate and that the proposed schemes operate close to absolute performance bounds, even for a moderate number of users.

Original languageEnglish
Pages (from-to)1424-1434
Number of pages11
JournalIEEE Journal on Selected Areas in Communications
Volume25
Issue number7
DOIs
Publication statusPublished - Sep 2007
Externally publishedYes

Keywords

  • Broadcast channels
  • MIMO systems
  • Scheduling

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