Optimizing user selection schemes in vector broadcast channels

Meng Wang, Tharaka Samarasinghe, Jamie S Evans

Research output: Contribution to journalArticleResearchpeer-review

8 Citations (Scopus)


In this paper, we focus on the ergodic downlink sum-rate performance of a system consisting of a set of heterogeneous users. We study three user selection schemes to group near-orthogonal users for simultaneous transmission. The first scheme is a random selection policy that achieves fairness, but does not exploit multi-user diversity. The second scheme is a greedy selection policy that fully exploits multi-user diversity, but does not achieve fairness, and the third scheme achieves fairness while partially exploiting multi-user diversity. We also consider two beamforming methods for data transmission, namely, maximum-ratio transmission and zero-forcing beamforming. In all scheduling schemes studied in the paper, there is a key parameter that controls the degrees of orthogonality of channel directions between co-scheduled users. We focus on optimally setting this parameter for each scheduling scheme such that the ergodic downlink sum-rate is maximized. To this end, we derive analytical expressions for the ergodic downlink sum-rate considering each scheduling scheme. Numerical results are also presented to provide further insights.
Original languageEnglish
Pages (from-to)565 - 577
Number of pages13
JournalIEEE Transactions on Communications
Issue number2
Publication statusPublished - 2015


  • User selection
  • broadcast channels
  • beamforming
  • heterogeneous users

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