在無線通訊系統中，多輸入多輸出(Multiple-input multiple-output, MIMO)技術已被廣泛用來增加傳輸速率與改善傳輸品質。為了有效地從接收到的訊號解回傳送端送出的資訊，多輸入多輸出偵測技術已被廣泛應用於接收端設計，且依偵測器之輸出格式可將其分為硬式輸出(Hard-output)與軟式輸出(Soft-output)兩大類。近年來，歸因於硬式輸出偵測器的效能極限，軟式輸出偵測器與渦輪解碼器所共同組成的渦輪多輸入多輸出系統被提出以增進整體系統效能；但是若影響系統效能甚大的偵測器軟式資訊不可靠，則整體系統效能反而會大幅度地降低。
　　為了解決上述問題，本論文針對4×4多輸入多輸出架構，探索如何提升偵測器與渦輪解碼器疊代運算系統之資訊可靠度，進而增進整體之系統效能。首先，藉由探討不同的對數相似比值(Log-likelihood ratio, LLR)計算方式，並利用同位檢查位元(Parity check bits)的資訊以更進一步改善多輸入多輸出偵測器軟式輸出的可靠度。此外，本論文更探討易於硬體實現的固定複雜度球型解碼(Fixed-complexity sphere decoding, FSD)多輸入多輸出偵測器，但由於固定複雜度球型偵測器會導致系統效能衰退，本文使用所提出的累積候選節點概念，搭配軟性輸入軟性輸出偵測器以有效地擴展候選節點，以補償原先之效能損失，最後並利用一個準則判斷累積候選節點數目是否穩定，以略過不必要的樹狀搜尋。與相關的渦輪多輸入多輸出系統相比，本文使用之方法只需較低的運算複雜度，便可達到與傳統渦輪多輸入多輸出系統相近的系統效能。

The multiple-input multiple-output (MIMO) technique has been widely used in many wireless communication systems to increase the transmission rate and improve the signal quality. To recover the transmitted signals from the received signals efficiently, several MIMO detection algorithms are applied in the receiver. These algorithms can be generally divided into hard-output and soft-output detection according to the types of detected output. Due to the performance limitation of hard-output MIMO detectors, turbo-MIMO systems have been proposed to combine the soft-output MIMO detector and the turbo decoder to enhance the overall system performance in recent studies. However, if the reliability of the soft-output information, which affects the system performance significantly, is not reliable, the overall system performance may not be acceptable.
To solve the above problem, this thesis explores methods to improve the reliability information of a combination of the iterative detector and the turbo decoder in 4×4 MIMO systems. Firstly, the study discusses the computation methods of log-likelihood ratio (LLR) and shows that the reliability of soft-output information in MIMO detectors can be further improved if the information of parity check bits is included,. The fixed-complexity sphere decoding (FSD) is then applied to MIMO detector design as this algorithm is conducive to hardware implementation. Since the original FSD algorithm may cause performance degradation, an accumulated candidate nodes (ACN) technique is proposed to expand potential nodes in soft-input soft-output MIMO detector so as to compensate for the degradation. Moreover, when the number of candidate nodes is stable enough, a criterion can then be used to ignore some tree search processes originally required. Compared to related turbo-MIMO systems, the proposed methods can achieve a decoding performance similar to that of the conventional system with lower computational complexity.

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