Selection relaying with transmit beamforming

A comparison of fixed and variable gain relaying

Phee Lep Yeoh, Maged Elkashlan, Iain B. Collings

Research output: Contribution to journalArticle

37 Citations (Scopus)


This paper presents a comparison and analysis of selection relaying with transmit beamforming as an effective approach to combat channel impairments in relay-assisted cellular networks. We consider the downlink scenario where the base station equipped with N antennas transmits to the mobile station either directly, or indirectly via a relay station, according to the link with the strongest received signal-to-noise ratio (SNR). We compare two amplify-and-forward protocols: i) fixed gain relaying which requires partial channel state information (CSI), and ii) variable gain relaying which requires full CSI. We present new exact closed-form expressions for the generalized moments of the end-to-end SNR to characterize the higher-order statistical properties of the SNR. We derive new exact closed-form expressions for the symbol error rate (SER), which are valid for a wide variety of modulations. Furthermore, we explicitly characterize the asymptotic behavior of the SER to obtain two key performance parameters: the array gain and the diversity order. Based on these, we reveal that the SNR advantage of variable over fixed gain relaying vanishes in the large N limit.

Original languageEnglish
Article number5756421
Pages (from-to)1720-1730
Number of pages11
JournalIEEE Transactions on Communications
Issue number6
Publication statusPublished - Jun 2011
Externally publishedYes


  • Beamforming
  • diversity methods
  • fading channels
  • wireless relays

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