5.1 結論
近年來，擴展頻譜通訊（Spread Spectrum Communcation-SSC）技術在碼分多 址 (CDMA) 等民用通訊中的應用也開始越來越受到人們的重視。本論文在研究了展 頻通訊系統的原理和直接序列展頻通訊系統的基礎上，分析了展頻碼序列的自(互) 相關函數、平衡性等性能指標，對當前 DS-CDMA 展頻通訊系統的調變模擬方法進行 了研究和探討。在此基礎上，為了提升系統效能，研究了將錯誤更正碼和展頻碼的 結合設計方式。從通道編碼率與展頻因子的抉擇，到極低編碼率之通道編碼設計，
以及近來的串接碼設計。由這些結合設計之分析可知，通道編碼與展頻碼的結合設 計，將獲得比傳統系統更佳的系統效能表現。此兩元件之結合設計，將是未來直序 展頻系統的主要研究方向。
5.2 後續研究建議
對於一直序展頻系統之輸出序列集合，其序列擁有錯誤更正能力與區隔不同使 用者之能力，然而該系統之發射端與接收端要如何設計，才能達到最佳系統效能，
為後續研究之方向。以下幾點有待後續的工作中繼續研究：
1.極低編碼率之通道編碼解碼器設計。由於編碼率愈低，其解碼複雜度愈高，
增加實現的難度，因此該如何降低解碼器之複雜度，乃一研究方向。
2. 串接碼之編碼器、解碼器於直序展頻通訊系統之設計研究。可視為一極低
編碼率通道編碼之替代方案。因解碼之複雜度高，因此將極低碼率之通道編碼以兩 個編碼率較高的通道編碼取代，除了降低解碼之複雜度，亦可善用軟解碼 (Soft decoding) 以及疊代解碼 (Iterative decoding) 的方式，大幅降低訊息位元錯誤 率與提高系統效能。
3. 特徵序列之研究。對於不同的通道編碼輸出碼字集合，特徵序列該如何選 取，才能把其餘使用者之干擾分量降至最低，以最佳化系統效能。
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