合作式通訊主要是在傳送端以及接收端之間加入數個中繼站協助傳輸，本文中假設這些中繼站以及傳送接收各端點都只有一根天線可以接收以及傳輸訊號，在中繼站中將訊號轉傳至接收端時我們使用SAF(Semi-blind Amplify and Forward) 將訊號放大，這樣的作法是為了減少第一段通道衰減對於訊號的影響，我們考慮的是一個雙向半雙工的合作式通訊系統，這樣的系統是兩個使用者彼此透過中繼站傳訊息給對方，而且每一個節點都是半雙工的裝置，代表的是同一時間只能接收或是傳輸訊號，由於我們每次只選擇一個中繼站傳入訊號因此中繼站的選擇機制也尤其重要，我們在一般中繼站的基礎下也討論了有buffer 幫助下的合作式系統，buffer 的協助雖然可以提升傳輸效率降低位元錯誤率，但是也將延遲變異數提高，因此我們最後提出了在此雙向合作式系統下兼顧位元錯誤率以及延遲變異數的折衷方案。

In wireless communication networks, signals received by destination usually suffer
from multipath fading and noises. Cooperative diversity can mitigated the multipath fading phenomenon. The two-way relay channel is a basic cooperative network, where two users exchanged independent messages with the intermediate relay. We assume each terminal is half duplex, that only can transmmit or receive messages each time, and each terminal is equiped one antenna. There were many kinds of relay forwarding protocols, which including AF(Amplify and Forward), DF(Decode and Forward), CF(Compress and Forward), applying in several two-way relaying protocols with different complexities and performances. Relay selection scheme is also a important issue in transmition efficiency, so we study different relay selection scheme in two-way cooperative system. The two-way system can improve spectral efficency, but it makes delay variance higher. In this thesis we propose new methods to reduce delay variance.

[1] Jaweria Amjad, Momin Uppal, and Saad Qaisar. Multi-level compress and forward coding for half-duplex relays. In 2012 IEEE Global Communications Conference (GLOBECOM), pages 4536–4541, 2012.
[2] A. Bletsas, A. Khisti, D.P. Reed, and A. Lippman. A simple cooperative diversity
method based on network path selection. IEEE J. Sel. Areas Commun., 24(3):659–672, 2006.
[3] Ming-Xian Chang and Yu.T. Su. Model-based channel estimation for ofdm signals in rayleigh fading. IEEE Trans. Wireless Commun., 50(4):540–544, 2002.
[4] Sheng-Lun Chiou, Kuo-Wang Hsieh, and Ming-Xian Chang. Csi reduction of mimo-ofdm systems by parameterization. In 2008 IEEE 19th International Symposium on Personal, Indoor and Mobile Radio Communications, pages 1–5, 2008.
[5] Dinh-Thuan Do. A study on af two-way relaying networks with imperfect channel estimation. In The 20th Asia-Pacific Conference on Communication (APCC2014), pages 450–453, 2014.
[6] M.O. Hasna and M.-S. Alouini. End-to-end performance of transmission systems with relays over rayleigh-fading channels. IEEE Trans. Wireless Commun., 2(6):1126–1131, 2003.
[7] M.O. Hasna and M.-S. Alouini. A performance study of dual-hop transmissions with fixed gain relays. In 2003 IEEE International Conference on Acoustics, Speech, and Signal Processing, 2003. Proceedings. (ICASSP ’03)., volume 4, pages IV–189, 2003.
[8] Aissa Ikhlef, Diomidis S. Michalopoulos, and Robert Schober. Max-max relay selection for relays with buffers. IEEE Trans. Wireless Commun., 11(3):1124–1135, 2012.
[9] Ioannis Krikidis, John Thompson, Steve Mclaughlin, and Norbert Goertz. Amplify-and-forward with partial relay selection. IEEE Commun. Lett., 12(4):235–237, 2008.
[10] Enyu Li, Shizhong Yang, and Haowei Wu. A source-relay selection scheme in two way amplify-and-forward relaying networks. IEEE Commun. Lett., 16(10):1564–1567, 2012.
[11] Huaping Liu, Petar Popovski, Elisabeth de Carvalho, and Yuping Zhao. Sum-rate optimization in a two-way relay network with buffering. IEEE Commun. Lett., 17(1):95–98, 2013.
[12] Lingyang Song. Relay selection for two-way relaying with amplify-and-forward protocols. IEEE Trans. Veh. Technol., 60(4):1954–1959, 2011.
[13] Tairan Wang, Alfonso Cano, Georgios B. Giannakis, and J. Nicholas Laneman. High-performance cooperative demodulation with decode-and-forward relays. IEEE Trans. Commun., 55(7):1427–1438, 2007.