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International Journal of Information Technology & Computer Science ( IJITCS )

Abstract :

Two conflicting challenges are how to maintain the interferences generated by the cognitive radio network to the primary network below an acceptable threshold level while maximizing the sum-rate of the cognitive radio network. We present two beamforming methods, modified zero forcing beamforming and transmit-receive beamforming. The zero forcing beamforming is modified by adding the channel gain between the cognitive radio base station and the primary user to meet the two conflicting goals. The orthogonality of transmit beams in MIMO beamforming by Gram-Schmidt method achieves the first goal that the primary user is interference free. To satisfy the second goal, self-interference is reduced by the constrained minimization of the mean output array of cognitive receivers. To reduce complexity of the system, the number of cognitive radio users must be limited. Criteria to select the number of best cognitive radio users should increase the sum-rate of cognitive-radio network. Subspace-based scheduling scheme selects the cognitive radio users orthogonal each other as much as possible so that the self-interference is mitigated. Simulation results are given to evaluate the performances of the proposed methods in forms of symbol error rates and sum-rates.

Keywords :

: beamforming, cognitive radios, constrained optimization

References :

  1. Federal Communications Commission, “Spectrum policy task force,” Rep. ET Docket no. 02-135, Nov. 2002.
  2. I. F. Akyildiz, W. Lee, M. C. Vuran, and S. Mohanty, “A survey on spectrum management in cognitive radio networks,” IEEE Commun. Magazine, pp. 40-48, Apr. 2008.
  3. C. Cordeiro, K. Challapali, D. Birru and S. Shankar, “IEEE 802.22: an introduction to the first wireless standard based on cognitive radios,” Journal of Commun., Vol. 1, No. 1, pp. 38-47, Apr. 2006.
  4. B. A. Fette, “Cognitive radio technology”, Academic Press, 2nd edition, 2009.
  5. K. Hamdi, W. Zhang, and K. B. Lataief, “Joint beamforming and scheduling in cognitive radio networks,” IEEE GLOBECOM, pp. 2977-2981, Nov. 2007.
  6. W. Zong, S. Shao, Q. Meng, and W. Zhu, “Joint user scheduling and beamforming for underlay cognitive radio system,” 15th IEEE Asia-Pacific Conf. on Commun., pp. 99-103, Oct. 2009.
  7. X. Wei, Y. ChangChung, and Y. GuangXin, “Joint beamforming and scheduling in the downlink of cognitive radio networks,” Springer Science in China Series F: Information Sciences, Vol. 52, No. 12, pp. 2324-2331, Dec. 2009.
  8. Y. Kwon, H. Kim, J. Yoo, and J. Chung, “Orthogonal beamforming methodology in cognitive radio networks,” 3rd Int. Conf. on Cognitive Radio Oriented Wireless Networks and Commun., pp. 1-5, May 2008.

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