合作式通訊已經被証實為一種有效的空間分集技術，可減輕由於衰落所產生的訊號損壞。現有的中繼站選擇機制中，幾乎所有的訊號源會透過相同中繼站的支援。除此之外，中繼站的傳輸功率會根據訊號源來分割。在總功率有限的情況下，由於用來幫忙每個訊號源的中繼站功率過低，因而導致不可靠的傳輸。為了解決這個問題，本論文提出兩種中繼站選擇機制。第一項機制是「權重式中繼站選擇機制」，為一種集中式的中繼站選擇機制。在權重式中繼站選擇機制中，目的端分配每個中繼站一項權重，用於中繼站的選擇。另一項機制為分散式的選擇機制，稱為「負載量式中繼站選擇機制」，在此機制中，每個中繼站計算在成功轉傳的條件下，可負擔的最多訊號源個數。根據模擬所得的結果，兩種所提出的機制之中斷機率效能皆優於現有參考文獻機制，並且能完全利用中繼站提供的分集效益。除此之外，「負載量式中繼站選擇機制」可降低整體的中繼站功率消耗。

Cooperative communication has been validated as one of the most effective spatial diversity techniques to mitigate channel impairments due to fading. In classical relay selection schemes, all source nodes tend to be supported by the same relay. Under the constraint of total transmit power, the relay power allocated to help the source node may not be sufficient to ensure successful transmission. The first scheme referred to as “weighted-CSI-based relay selection scheme” is a centralized relay selection scheme. The destination assigns each relay a weight for relay selection, which is determined on the channel condition and relay utilization rate. The second scheme is a distributed relay selection scheme, called “affordable load based (AL-based) relay selection scheme”, where each relay computes the maximum number of source that it can support without incurring errors. Simulations are performed to demonstrate the performance of the proposed schemes. Both the proposed schemes outperform traditional CSI-based relay selection scheme in terms of outage performance and can achieve full diversity equal to the number of relay. Furthermore, the AL-based scheme reduces the total relay power consumption for relay cooperation by effectively making use of relay power.

[1] C. Oestges and B. Clerckx, MIMO Wireless Communications. Academic Press Inc., 2007.
[2] A. F. Molisch and M. Z. Win, “Mimo systems with antenna selection,”IEEE Micro., vol. 5, no. 1, pp. 46–56, March 2004.
[3] A. Nosratinia, T. Hunter, and A. Hedayat, “Cooperative communication in wireless networks,” IEEE Commun. Mag., vol. 42, no. 10, pp. 74–80, October 2004.
[4] R. Pabst, B. H. Walke, D. C. Schultz, P. Herhold, H. Yanikomeroglu, S. Mukherjeee, H. Viswanathan, M. Lott, W. Zirwas, M. Dohler, H. Aghvami, D. D. Falconer, and G. P. Fettweis, “Relay-based deployment concepts for wireless and mobile broadband radio,” IEEE Commun. Mag., vol. 42, no. 9, pp. 80–89, September 2004.
[5] J. N. Laneman, D. N. C. Tse, and G. W. Wornell, “Cooperative diversity in wireless networks: Efficient protocols and outage behavior,” IEEE Trans. Inform. Theory, vol. 50, no. 12, pp. 3062–3080, December 2004.
[6] A. Bletsas, A. Khisti, D. P. Reed, and A. Lippman, “A simple cooperative diversity method based on network path selection,” IEEE J. Select. Areas Commun., vol. 24, no. 3, pp. 659–672, March 2006.
[7] E. Beres and R. Adve, “Selection cooperation in multi-source cooperative networks,”IEEE Trans. Wireless Commun., vol. 7, no. 1, pp. 118–127, January 2008.
[8] T. Wang, T. Cano, G. B. Giannakis, and J. N. Laneman, “High-performance cooperative demodulation with decode-and-forward relays,” IEEE Trans. Commun., vol. 55, no. 7, pp. 1427–1438, July 2007.
[9] Y. Zhao, R. Adve, and T. J. Lim, “Improving amplify-and-forward relay networks: optimal power allocation versus selection,” IEEE Trans. Wireless Commun., vol. 6, no. 8, pp. 3114–3123, August 2007.
[10] M. O. Hasna and M.-S. Alouini, “A performance study of dual-hop transmissions with fixed gain relays,” IEEE Trans. Wireless Commun., vol. 3, no. 6, pp. 1963–1968, November 2004.
[11] A. Ribeiro, X. Cai, and G. B. Giannakis, “Symbol error probabilities for general cooperative links,” IEEE Trans. Wireless Commun., vol. 4, no. 3, May 2005.
[12] J. N. Laneman and G. W.Wornell, “Distributed space time coded protocols for exploiting cooperative diversity in wireless networks,” IEEE Trans. Inform. Theory, vol. 49, no. 10, pp. 2415–2525, October 2003.
[13] V. Sreng, H. Yanikomeroglu, and D. Falconer, “Relay selection strategies in cellular networks with peer-to-peer relaying,” in Proc. IEEE Veh. Technol. Conf., October 2003, pp. 1949–1953.
[14] J. Luo, R. S. Blum, L. J. Cimini, L. J. Greenstein, and A. M. Haimovich, “Decodeand-forward cooperative diversity with power allocation in wireless networks,”IEEE Trans. Wireless Commun., vol. 6, no. 3, pp. 793–799, March 2007.
[15] V. A. Le, R. A. Pitaval, S. Blostein, T. Riihonen, and R. Wichman, “Green cooperative communication using threshold-based relay selection protocols,” in Proc. ICGCS, June 2010, pp. 521–526.
[16] T. E. Hunter and A. Nosratinia, “Distributed protocols for user cooperation in multi-user wireless networks,” in Proc. IEEE GLOBECOM, November 2004, pp. 3788–3792.
[17] J. Zhang, Q. Zhang, C. Shao, Y. Wang, P. Zhang, and Z. Zhang, “Adaptive optimal transmit power allocation for two-hop non-regenerative wireless relaying system,” in Proc. IEEE Veh. Technol. Conf., May 2004, pp. 1213–1217.
[18] M. O. Hasna and M.-S. Alouini, “Optimal power allocation for relayed transmissions over rayleigh-fading channels,” IEEE Trans. Wireless Commun., vol. 3, no. 6, pp. 1999–2004, November 2004.
[19] T. E. Hunter and A. Nosratinia, “Cooperation diversity through coding,” in Proc. IEEE Int. Symp. Inform. Theory, July 2002.
[20] Z. Lv, Z. Yu, and H. Liu, “Multi-user cooperative communication based on linear network coding,” J. of Comput. Inform. Syst., no. 2, pp. 801–807, January 2012.
[21] M. Mehta, S. Khakurel, and A. Karandikar, Buffer-based channle dependent uplink scheduling in relay-assisted lte networks,” in Proc. IEEE WCNC, April 2012, pp. 1777–1781.
[22] F. A. Ona, A. Adinoyi, Y. Fan, H. Yanikomeroglu, J. S. Thompson, and I. D. Marsland, “Threshold selection for snr-based selective digital relaying in cooperative
wireless networks,” IEEE Trans. Wireless Commun., vol. 7, pp. 4226–4237, November 2008.
[23] P. Herhold, E. Zimmermann, and G. Fettweis, “A simple cooperative extension to wireless relaying,” in Proc. Int. Zurich Seminar on Commun., February 2004, pp. 36–39.
[24] H. Chen and M. Guizani, Next Generation Wireless Systems and Networks. John Wiley and Sons Ltd., 2006.
[25] M. Yuanyuan, Z. Sihai, and Z. Wuyang, “Joint channel-topology based opportunistic relay selection strategy,” in Int. Conf. on Wireless Commun. and Signal Proc., November 2009, pp. 1–4.
[26] L. Sun, T. Zhang, L. Lu, and H. Niu, “On the combination of cooperative diversity and multiuser diversity in multi-source multi-relay wireless networks,” IEEE
Signal Process. Lett., vol. 17, no. 6, pp. 535–538, June 2010.
[27] H. Ding, J. Ge, D. B. D. Costa, and Z. Jiang, “A new efficient low-complexity scheme for multi-source multi-relay cooperative networks,” IEEE Trans. Veh. Technol., vol. 60, no. 2, pp. 716–722, Feburary 2011.
[28] A. Bletsas, H. Shin, and M. Z. Win, “Cooperative communications with outageoptimal opportunistic relaying,” IEEE Trans. Wireless Commun., vol. 6, pp. 3450–3460, September 2007.
[29] J. N. Laneman, G. W. Wornell, and D. N. C. Tse, “An efficient protocol for realizing cooperative diversity in wireless networks,” in Proc. IEEE Int. Symp. Inform. Theory, June 2001.