合作式通訊技術為近年來無線通訊領域增強訊號之可靠度、達到系統空間多樣性的一項有效技術，該技術主要使用中繼端之協助，傳送訊息至目的端，藉此改善整體系統之效能。

本論文中，我們針對估測後傳送的中繼模式，在目的端使用最大概似估計法則對收到之訊號做決策，進而與放大後傳送、解碼後傳送的中繼端模式做系統效能之比較。在此，我們更試著分配來源端與中繼端的傳輸功率，促使系統平均位元錯誤率最低，並找出最佳功率分配方式。依據模擬的結果，分析三種不同中繼端傳送模式的優劣，我們得知三種中繼模式透過功率分配，系統效能皆有著較好的表現，且中繼端與來源端距離之遠近，將影響三種不同模式之系統效能。

另外一項研究重點，我們將針對使用估測後傳送之模式，推導其理論分析式計算位元錯誤率，在此，提出一個高斯近似之方法，利用此方法我們則可成功推導出此系統之理論分析式，經由電腦模擬驗證，顯示理論值與電腦模擬結果在中繼端與來源端之距離較小時，兩者結果相當吻合，即不需要電腦複雜的反覆模擬即可求得系統最低位元錯誤率。

Cooperative communication is an effective technique recently proposed to enhance signal reliability and get spatial diversity in wireless communication field.

In this thesis, for the estimate-and-forward (EF) relay mode, we use the maximum likelihood estimation (MLE) detector in the destination node to make decision for received signals. Then, we compare its system performance with amplify-and-forward (AF) and decode-and-forward (DF) mode schemes. We also try to allocate the power assigned to the source node and the relay node, so that the system bit error rate (BER) is minimized. According to the simulation results, we analyze the advantages and the disadvantages among the three different relay transmission modes. The conclusion is that this three relay modes have better BER performance when power allocation is utilized. And the distance between the relay and the source will affect the performance of this three relay modes.

Another contribution of our work is that for the EF mode, we derive the formula to calculate its BER.We propose a Gaussian approximation method. With this method the formula can be derived successfully. As verified by simulation, it is observed that the simulation results almost match the BERs that are calculated by the formula. Therefore, we do not need to use complex computer simulation to achieve the optimal BER. Instead, we can take advantage of the afore-mentioned BER formula to do it.

[1] T. Himsoon, W.P. Siriwongpairat, Z. Han, and K.J.R. Liu, "Lifetime maximization via cooperative nodes and relay deployment in wireless networks,"
IEEE Journal on Selected Areas in Communs., vol. 25, no. 2, pp. 306-317, Feb. 2007.
[2] A. Nosratinia, T.E. Hunter, and A. Hedayat, "Cooperative communication in wireless networks," IEEE Communs. Magazine, vol. 42, no. 10, pp. 74-80, Oct. 2004.
[3]C.I. Serediuc, J. Lilleberg, and B. Aazhang, "MAP detection with soft information in an estimate and forward relay network," Conf. Record of the Forty Fourth Asilomar Conf. on Signals, Systems and Computers, pp. 121-125, Nov. 2010.
[4]Z. Zhou, S. Zhou, S. Cui, and J.H. Cui, "Energy-efficient cooperative communication in a clustered wireless sensor network," IEEE Trans. on Vehicular Technology, vol. 57, no. 6, pp. 3618-3628, Nov. 2008.
[5]Y.W. Hong, W.J. Huang, F.H. Chiu, and C.C.J Kuo, "Cooperative communications in resource-constrained wireless networks" IEEE Signal Processing Magazine., vol. 24, no. 3 pp. 47-57, May. 2007.
[6]E. C. van der Meulen, "Three-terminal communication channels," Adv. Appl. Prob.,
vol. 3, pp.120-154, 1971.
[7]T. Cover and A. E. Gamal, "Capacity theorems for the relay channel," Trans. on Info. Theory, vol. 25, no. 5, pp. 572-584, Sept. 1979.
[8]R. Yu, and T. Wu, "Joint network coding and channel coding for cooperative relay communication system," IEEE International Conf. on Wireless Communs. and Signal Processing, pp. 1-4, Oct. 2010.
[9]H. Li and Q. Zhao, "Distributed modulation for cooperative wireless communications," IEEE Signal Processing Magazine, vol. 23, no. 5, pp. 30-36, Sept. 2006.
[10]Y. Li and D. Samb, "Performance analysis of relay channel with amplify-and-forward in cooperative communication system," IEEE International Conf. on Computer Science and Information Technology, vol. 7, pp. 565-568, July. 2010.
[11]L. Zhang and L.J. Cimini, "Cooperative network coding in selective decode-and-forward networks with multiple source-destination pairs," Annual Conf. on Information Sciences and Systems, pp. 521-526, Mar. 2008.
[12]A. Sendonaris, E. Erkip, and B. Aazhang, "User cooperation diversity. part i. system description" and "part ii. implementation aspects and performance analysis," IEEE Trans. Communs., vol. 51, no. 11, Nov. 2003.
[13]I. Abou-Faycal and M. Medard, "Optimal uncoded regeneration for binary antipodal signaling," IEEE International Conf. on Communs., vol. 2, pp. 742-746, Jun. 2004.
[14]C. Wang, L. Li, W. Wang, Y. Zhang, L. Song, and J. Lilleberg, "A simplified estimate-and-forward scheme for relay networks," IEEE Vehicular Technology Conf., pp. 1-5, Sept. 2011.
[15]T. Cui, T. Ho, and J. Kliewer, "Some results on relay strategies for memoryless two-way relay channels," Information Theory and Applications Workshop, pp. 158-164, Jan. 2008.
[16]K. S. Gomadam and S. Jafar, "Optimal relay functionality for SNR maximization in memoryless relay networks," IEEE Journal on Selected Areas in Communs., vol. 25, no. 2, pp. 390-401, Feb. 2007.
[17]G. L. Stuber, Principles of Mobile Communication. Kluwer Academic Publishers 2001.
[18]B. Sklar, Digital Communications - Fundamental and Applications. Prentice-Hall International, Inc. 2001.
[19]P. Weitkemper and G. Dietl, "Maximum likelihood receiver for MMSE relaying," IEEE International Conf. on Communs., pp. 1-5, June. 2011.
[20]G. W. Stewart, Afternotes goes to Graduate School - Lectures on Advanced Numerical Analysis. SIAM 1998.