Protocol design and delay analysis of half-duplex buffered cognitive relay systems

  • Authors:

  • Yan Chen;Vincent K. N. Lau;Shunqing Zhang;Peiliang Qiu

  • Affiliations:

  • Huawei Technologies, Shanghai, China and Institute of Information and Communication Engineering, Zhejiang University, Hangzhou, China;Department of Electronic and Computer Engineering, Hong Kong University of Science and Technology, Kowloon, Hong Kong;Department of Electronic and Computer Engineering, Hong Kong University of Science and Technology, Kowloon, Hong Kong;Institute of Information and Communication Engineering, Zhejiang University, Hangzhou, China

  • Venue:
  • IEEE Transactions on Wireless Communications
  • Year:
  • 2010

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Abstract

In this paper, we quantify the benefits of employing relay station in large-coverage cognitive radio systems which opportunistically access the licensed spectrum of some smallcoverage primary systems scattered inside. Through analytical study, we show that even a simple decode-and-forward (SDF) relay, which can hold only one packet, offers significant pathloss gain in terms of the spatial transmission opportunities and link reliability. However, such scheme fails to capture the spatial-temporal burstiness of the primary activities, that is, when either the source-relay (SR) link or relay-destination (RD) link is blocked by the primary activities, the cognitive spectrum access has to stop. To overcome this obstacle, we further propose buffered decode-and-forward (BDF) protocol. By exploiting the infinitely long buffer at the relay, the blockage time on either SR or RD link is saved for cognitive spectrum access. The buffer gain is shown analytically to improve the stability region and average end-to-end delay performance of the cognitive relay system.