多載波分碼多工系統之多使用者偵測器

Abstract

由於多載波分碼多工系統(MC-CDMA)擁有高資料傳輸的能力，因此，它是未來無線通訊中具有潛力的調變方式。然而，多使用者的干擾是限制這項能力的主因之一。雖然，傳統線性最小平均平方差(LMMSE)偵測器有著很好的效果，但是它的計算複雜度很高。另一方面，平行干擾消除(PIC)偵測器亦可以有好的表現，但是它在前級可能造成錯誤的偵測。在本篇論文中，我們提出新的方法來解決這些問題。首先我們藉由多載波通道的特性，提出一個新的線性最小平方差之方法來減少參數。為了降低平行干擾消除的決策錯誤，我們提出有部份消除因子(PCF)的部份平行干擾消除來控制干擾的消除。其中部份消除因子是用最小平方差的作法求出。模擬顯示：我們提出的線性最小平方差之方法有著和傳統作法相似的效果，而且部份平行干擾消除偵測器也有較以前的作法有更好的效果。

Due to its high-data rate transmission capability, multi-carrier code division multiple access (MC-CDMA) systems have attained increasing significance in wireless communications. The multi-user interference is one of the main factors limiting the system capacity of a MC-CDMA system. While the conventional linear minimum mean square error detector (LMMSE) has good performance, its computational complexity is high. The parallel interference cancellation (PIC) detector can have good performance; however, it may have incorrect decisions in the early stages. In this thesis, we propose new methods to overcome these problems. Using the multi-carrier channel characteristics, we propose a new LMMSE method such that the number of the combining weights can be significantly reduced. To reduce decision errors in the PIC detector, we propose a partial PIC approach in which partial cancellation factors (PCF) are introduced to control the interference cancellation level. Optimal PCFs are derived using a MMSE criterion. Simulations show that the proposed LMMSE method can have the similar performance as conventional ones. The proposed partial PIC detector can outperform the full PIC detector.