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Träfflista för sökning "swepub ;pers:(Ottersten Björn 1961);lar1:(kth);pers:(Zheng Gan);srt2:(2009);conttype:(refereed)"

Sökning: swepub > Ottersten Björn 1961 > Kungliga Tekniska Högskolan > Zheng Gan > (2009) > Refereegranskat

  • Resultat 1-4 av 4
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1.
  • Zheng, Gan, et al. (författare)
  • Collaborative-Relay Beamforming with Perfect CSI : Optimum and Distributed Implementation
  • 2009
  • Ingår i: IEEE Signal Processing Letters. - IEEE. - 1070-9908. ; 16:4, s. 257-260
  • Tidskriftsartikel (refereegranskat)abstract
    • This letter studies the collaborative use of amplify-and-forward (AF) relays to form a virtual multiple-input single-output (MISO) beamforming system with the aid of perfect channel state information (CSI) in a flat-fading channel. In particular, we optimize the relay weights jointly to maximize the received signal-to-noise ratio (SNR) at the destination terminal with both individual and total power constraints at the relays. We show that the optimal collaborative-relay beamforming (CRB) solution achieves the full diversity of a MISO antenna system. Another main contribution of this letter is a distributed algorithm that allows each individual relay to learn its own weight, based on the Karush-Kuhn-Tucker (KKT) analysis.
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2.
  • Zheng, Gan, et al. (författare)
  • Robust and distributed beamforming
  • 2009
  • Ingår i: 2009 International Conference on Wireless Communications and Signal Processing. - 978-1-4244-4856-2 ; s. 1629-1633
  • Konferensbidrag (refereegranskat)abstract
    • This paper studies the use of amplify-and-forward (AF) relays for robust beamforming, with the aid of imperfect channel state information (CSI) at the sender. In particular, the maximization of the worst-case signal-to-noise ratio (SNR) at the destination terminal is studied under a bounded spherical region for the norm of CSI error vector. We show that under a condition on the estimated CSI quality, the robust-optimal collaborative-relay beamforming (CRBF) can be obtained by S-Procedure and rank relaxation techniques. In addition, a distributed algorithm is proposed by examining the structure of the optimal CRBF.
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3.
  • Zheng, Gan, et al. (författare)
  • Robust Cognitive Beamforming With Bounded Channel Uncertainties
  • 2009
  • Ingår i: IEEE Transactions on Signal Processing. - 1053-587X. ; 57:12, s. 4871-4881
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper studies the robust beamforming design for a multi-antenna cognitive radio (CR) network, which transmits to multiple secondary users (SUs) and coexists with a primary network of multiple users. We aim to maximize the minimum of the received signal-to-interference-plus-noise ratios (SINRs) of the SUs, subject to the constraints of the total SU transmit power and the received interference power at the primary users (PUs) by optimizing the beamforming vectors at the SU transmitter based on imperfect channel state information (CSI). To model the uncertainty in CSI, we consider a bounded region for both cases of channel matrices and channel covariance matrices. As such, the optimization is done while satisfying the interference constraints for all possible CSI error realizations. We shall first derive equivalent conditions for the interference constraints and then convert the problems into the form of semi-definite programming (SDP) with the aid of rank relaxation, which leads to iterative algorithms for obtaining the robust optimal beamforming solution. Results demonstrate the achieved robustness and the performance gain over conventional approaches and that the proposed algorithms can obtain the exact robust optimal solution with high probability.
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4.
  • Zheng, Gan, et al. (författare)
  • Robust Collaborative-Relay Beamforming
  • 2009
  • Ingår i: IEEE Transactions on Signal Processing. - IEEE. - 1053-587X. ; 57:8, s. 3130-3143
  • Tidskriftsartikel (refereegranskat)abstract
    • Relay communications is a promising technique to extend the range of wireless communications by forwarding the message from the sender to the intended destination. While fixed or variable-power relays have been previously investigated, this paper addresses the collaborative use of variable-phase variable-power amplify-and-forward (AF) relays for robust beamforming, with the aid of imperfect channel state information (CSI) at the sender. In particular, the maximization of the worst-case signal-to-noise ratio (SNR) at the destination terminal is studied under a bounded spherical region for the norm of the CSI error vector from the relays to the destination. Our main contribution is that we prove, under a condition on the quality of the estimated CSI, the robust-optimal collaborative-relay beamforming (CRBF) can be obtained by S-Procedure and rank relaxation techniques. In addition, a distributed algorithm is developed by examining the structure of the optimal CRBF solution. Results demonstrate a significant gain of CRBF over non-robust approaches.
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