在任何無線通訊領域中，訊號會受到雜訊、多路徑干擾和衰減效應的影響，合作式通訊利用透過鄰近節點作為中繼端將收到的訊號經過處理後轉傳給接收端，以補強點對點的傳輸可能受到通到衰減的影響，相比於MIMO在通訊設備中容納多跟天線，合作式通訊依靠中繼端的幫助達成空間上的多樣性。本論文採用中繼協定中的解碼後傳送作為資料轉傳的技術，並且搭配通道資訊及接收端使用不同多樣性結合的方式(例如: Selection Combining, Maximum Ratio Combining)，也提出類似典型結合的演算法降低錯誤率改善系統效能。
為了更有效率的傳送通到資訊，我們基於Karhunen-Loève Expnsion (KLE) 的概念提出回傳有效通道響應的估測值至傳送端的方法，並且利用高斯量化、RLS方法，減少通道係數傳遞的負載及誤差。

In the field of wireless communication, the signal will be affected by noise, multipath interference and fading effects. Through the neighbor nodes, the transmitted signal can be relayed to the destination. Cooperative communications can reinforce the point-to-point transmission channel. Compared with the Multiple-Input Multiple-Output(MIMO), cooperative communication relies on the help of the relay points to implement spatial diversity. To improve the performance of bit-error rate, this thesis applies decode and forward to send the signal to destination. With the channel state information (CSI) at receiver, we propose combining techniques and give the comparison with the traditional diversity combining like Selection Combining (SC) and Maximum Ratio Combining (MRC).
In order to efficiently forward the CSI, we propose an efficient method that forward the estimated channel responses (CRs) to the receiver based on the Karhunen-Loève Expansion(KLE), and then, we use Gaussian quantization and Recursive Least Squares (RLS) to reduce the load and the error of channel coefficient transmission.

[1] J. N. Laneman, D.N.C. Tse, and G. W. Wornell. “Cooperative diversity in wireless networks: Efficient protocols and outage behavior’’. IEEE Trans. On Inf Theory,50(12):3062-3080,Dec. 2004.
[2] A. K. Sadek, W. su, and K. J. R. liu. “Multinode cooperative communication in wireless networks’’. IEEE Trans. Signal Process.,vol. 55, no. 1 , pp. 341-355, Jan.2007
[3] A. Sendonaris, E. Erkip, and B. Aazhang, “User cooperation diversity -part I: System description,” IEEE Trans. Commun., vol. 51, no. 11, pp.1927-1938, Nov. 2003
[4] A. Sendonaris, E. Erkip, and B. Aazhang. “User cooperation diversity. Part ii. Implementation aspects and performance analysis’’. IEEE Trans. on Commun.,51(11):1939-1948,Nove 2003.
[5] A. Ribeiro, X. Cai, and G.B. Giannakis. “Symbol error probabilities for general cooperative links’’. IEEE Trans. on wireless Commun., 4(3):1264-1273, May 2005.
[6] Qian Li, Rose Qingyang Hu,Yi Qian and Geng Wu.” Cooperative communications for wireless networks: techniques and applications in LTE-advanced systems”. IEEE Trans. Vol.19, Apr.2012
[7] T. Wang, A. Cano, G. B. Giannakis, and J. N. Laneman. “High-performance cooperative demodulation with decode-and-forward relays’’. IEEE Trans. on Commun., 55(7):1427-1438, July 2007
[8] Y. Li, and X Huang, “The simulation of Independent Rayleigh Faders,’’ IEEE Trans. Commun.,vol. 50, No. 9,pp.1503-1514,Sept.2002.
[9] A. Kuhne, “throughput analysis of multi-user OFDMA-systems using imperfect CQI feedback and diversity techniques,” IEEE J. Select. Areas Commun., vol. 26, no. 8,pp. 1440 - 1450, October 2008.
[10] S.Guharoy, N.B. Mehta, “Joint Evaluation of Channel Feedback Schemes, Rate Adaptation, and Scheduling in OFDMA Downlinks With Feedback Delays,” IEEE Trans. Veh. Technol., vol. 62, No. 4, pp. 1719-1731, May 2013.
[11] S. Zhou, G. B. Giannakis, “Optimal transmitter eigen-beamforming and space-time block coding based on channel mean feedback,” IEEE Trans. Signal Processing, vol. 50, no. 10, pp. 2599-2613 ,Oct. 2002.
[12] Sheng-Lun Chiou, Kuo-Wang Hsieh, and Ming-Xian Chang, “CSI Reduction of MIMO-OFDM Systems by Parameterization,” in Proc. IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, 15-18. Sept.2008
[13] Ren-Shian Chen and Ming-Xian Chang, “CSI Feedback for closed-loop MIMO-OFDM systems based on B-splines,” in Proc. IEEE Globe Com Workshop 2010.
[14] M. X. Chang and Y. T. Su, “Model-based channel estimation for OFDM signals in Rayleigh fading,” IEEE Trans. Commun., vol. 50, pp. 540-544, Apr. 2002.
[15] D.J. Love, R.W. Heath. Jr., W. Santipach, M.L. Honig, “What is the value of limited feedback for MIMO channels” IEEE Commun. Mag vol. 42, No. 10, pp. 54-59, Oct. 2004.
[16] Tao Cui, “Blind Receiver Design for OFDM Systems Over Doubly Selective Channels,” IEEE Trans. Commun., vol. 55, no.5, pp. 906 - 917, May 2007.
[17] H. Zhang, Y. Li, V. Stolpman, and N. V. Waes, “A reduced CSI feedback approach for precoded MIMO-OFDM systems,” IEEE Trans. Wireless Commun., vol. 6, no. 1, pp. 55-58, Jan. 2007
[18] Channel State Information (CSI) Reduction in Frequency and Time Domain for Close-loop MIMO-OFDM Systems.
[19] Hoang Le Nam, “On The Performance Of Two-Way Amplify-And-Forward Relay Networks”