Limited feedback schemes for downlink OFDMA based on sub-channel groups

Jieying Chen*, Randall A. Berry, Michael L. Honig

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

60 Scopus citations

Abstract

In a downlink Orthogonal Frequency Division Multiple Access (OFDMA) system, optimally allocating sub-channels across mobile users can require excessive feedback of channel state information (CSI). We consider an OFDMA model in which the feedback overhead is explicitly taken into account, given a fixed feedback rate and finite coherence time. The tradeoff between feedback rate and sum capacity is studied for two limited feedback schemes: a sequential scheme in which the users send compressed feedback bits over consecutive time slots, and a contention scheme in which users send their feedback via a random access protocol. For both schemes each feedback bit indicates a request for a group containing multiple subchannels. We show that the sum capacity for both schemes with optimized sub-channel groups grows linearly with the number of sub-channels N, and that the associated constant increases as the log of the normalized feedback rate measured in bits per coherence time per sub-channel. We also compare the asymptotic (large N) performance of the two limited feedback schemes as a function of the feedback rate and load (users per sub-channel). The sequential scheme performs best with moderate to large feedback rates, or small loads, whereas the contention scheme performs best with small feedback rates or large loads.

Original languageEnglish (US)
Article number4641955
Pages (from-to)1451-1461
Number of pages11
JournalIEEE Journal on Selected Areas in Communications
Volume26
Issue number8
DOIs
StatePublished - Oct 2008

Keywords

  • Channel grouping
  • Downlink
  • Feedback overhead
  • Finite coherence time
  • Limited feedback
  • Multiuser
  • OFDMA

ASJC Scopus subject areas

  • Computer Networks and Communications
  • Electrical and Electronic Engineering

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