在合作式無線網路中，最常見的中繼站選擇機制為選擇一個最佳的中繼站來負責接收和轉傳，以提升分集增益。然而，不同於以往的中繼站選擇機制，最近的研究提出新的概念，其概念為分別選擇出最佳的接收和轉傳中繼站，以提升訊雜比增益，由於最佳的接收和轉傳中繼站不一定為同一個中繼站，中繼站需搭配緩衝區來暫存封包，因此此新概念雖可以提升訊雜比增益，但是會造成嚴重的封包延遲。

而我們的論文，在選擇最佳接收和轉傳中繼站的過程中，除了考慮通道狀況，還額外考慮緩衝區的狀況，其概念為在不影響系統效能下，均勻分配封包於每個中繼站，我們藉由理論分析，證明出我們系統的特性可以成功地均勻分配封包於每個中繼站，此外，我們的模擬結果顯示出，在達成相同訊雜比增益的條件下，相較於參考文獻的系統，我們的系統可以降低96%的封包延遲。

In this thesis, we study the relay selection problem for a finite buffer-aided decode-and-forward (DF) cooperative wireless network. In [1], the author proposed the max-max relay selection (MMRS), which selects the strongest source-relay (S-R) and the strongest relay-destination (R-D) channels for reception and transmission, respectively. Since MMRS may incur data loss when the relay buffer is full, infinite buffer must be assumed. A more practical scheme, called hybrid relay selection (HRS), which combines opportunistic relay (OR) and MMRS has also been proposed for relays with finite buffers. Although HRS achieves the same outage probability as MMRS with infinite buffer size, it incurs severe delay because of the prolonged initialization phase. To mitigate undesired delay for performing cooperative relaying, we propose composite relay selection (CRS), which combines OR and shortest-in longest-out (SILO), to utilize the channel and buffer status simultaneously. The proposed CRS is evaluated theoretically considering a toy example with two relays. Simulations are conducted to validate the analysis accuracy. Extensive comparisons of CRS and other related schemes are also presented. It is shown that the proposed CRS scheme significantly reduces the delay under the same outage probability compared with HRS. In terms of delay, the difference between CRS and HRS is 96% for K=3 relays and SNR=15 dB, and the improvement is more pronounced when the number of relays increases.

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