近幾年來，由於分碼多工存取系統(CDMA)比分時多工存取系統(TDMA)擁有較高容量、能抵抗多重路徑之衰減等許多優點，已成為一重要之通訊機制與實現3G無線網路系統的基本方法。然而，在傳送訊號時受到多重路徑影響的關係，使得接收端在接收某個傳送訊號時會因此接收到不同時間延遲，不同振幅衰減的加成訊號，進而造成解調還原時工作的困難。另一個造成干擾的原因則為多重存取干擾(MAI)，是由於在CDMA系統中，多位使用者同時在相同的頻帶上傳送訊息所造成。為了要消除這些干擾，數種多用戶偵測器曾被提出，其中包含了並列干擾消除偵測器(PIC)。在此論文中，我們提出一種附有延遲估測(Delay Estimation)功能的並列干擾消除偵測器。
現在已有一延遲估測的方法被提出，如利用最大可能區域法(Maximum Likelihood)以及近似最大可能區域法(Approximated Maximum Likelihood)，所得到的延遲估測。本文將提出一個延遲估測與干擾投影法之干擾消除接收器。比起原本的干擾消除接收器，我們不需知道用戶的傳送功率與訊號傳送中所造成的延遲，即可解調出用戶傳送的訊號。因此本文提出的此種接收器明顯地更合乎實際上的通訊狀況。之後再觀察經過數據模擬後，是否能因較準確的延遲與功率估測而得到較佳之接收效果。

Code Division Multiple Access (CDMA) becomes an important access scheme in recent years because of its several advantages such as higher capacity, anti-jamming. It also has emerged as the basic technique for the realization of the physical layer of third generation (3G) wireless network. However, because of the multipath fading effect, the receiver will receive many replicas of the transmitted signal. These replicas arrive at the receiver with slightly time differences and amplitude decay. This will cause the problem in demodulating received signal. Another source of interference is the multiple access interference (MAI). The multiple access interference is produced when there are multiple users using the same frequency band simultaneously in the CDMA system. In order to suppress the interference, several multiuser detectors have been proposed, including the parallel interference cancellation (PIC) scheme. In this thesis, an algorithm is proposed, which combines the interference cancellation scheme with delay estimation.
Some delay estimation methods have been proposed, e.g. delay estimation by ML and AML method. In this thesis, an interference cancellation receiver incorporating the delay estimation and the interference projection method is introduced. Compared to original interference cancellation receiver, we can demodulate the information signal without knowing the power of transmitted signal and the propagation delay. So, the proposed receiver is clearly more fit the practical communication situation. We can observe the parameter simulation to check if the demodulation performance gets better under the improvement of the performance of the delay estimation.

[1] R. L. Peterson, R. E. Ziemer, D. E. Borth, “Introduction to Spread Spectrum Communications”, Prentice Hall, 1995
[2] Mahesh K. Varanasi and Behnaam Aazhang, “Multistage Detection in Asynchronous Code-Division Multiple-Access Communications”, IEEE Trans. on Commun., vol 38, pp.509-519, 1990
[3] Lars K. Rasmussen, Teng J. Lim and Ann-Louise Johansson, “One-Shot Filtering Equivalence for Linear Successive Interference Cancellation in CDMA”, Vehicular Technology Conference, 47th, IEEE, pp.2163-2167, 1997
[4] 崔熙嬅, “結合干擾投影與並列干擾消除之CDMA多用戶偵測器” 國立清華大學碩士論文, 九十三年六月
[5] E.G. Strom, S. Parkvall, S.L. Miller, B.E. Ottersten, “Propagation delay estimation in asynchronous direct-sequence code-division multiple access systems”, IEEE Trans. Commun., vol. 44, pp. 84-93, 1996
[6] R.A. Iltis, “Exact and approximate maximum-likelihood parameter estimation for quasi-synchronous CDMA signals”, IEEE Trans. Commun., vol. 48, pp. 1208-1216, 2000
[7] Mahesh K. Varanasi and Behnaam Aazhang, “Near-Optimum Detection in Synchronous Code-Division Multiple-Access Systems”, IEEE Trans. on Commun., vol. 39, pp.725-736, 1991
[8] D. Divsalar, M. Simon, and D. Raphaeli, “Improved parallel interference cancellation for CDMA”, IEEE Trans. on Commun., vol. 46, pp. 258-268, 1998
[9] Dongning Guo, lars K. Rasmussen, Sumei Sun and Teng J. Lim, “A Matrix-Algebraic Approach to Linear Parallel interference Cancellation in CDMA”, IEEE Trans. on Commun., vol. 48, pp.152-161, 2000
[10] Simon Haykin, “Communication Systems”, Wiley, 2001
[11] John G. Proakis, “Digital communications”, Mc Graw Hill, 4th edition, 2001.
[12] T. S. Rappaport, “Wireless communications: principles and practice”, Prentice Hall 2nd edition, 2002
[13] I. Ziskind, M. Wax, “Maximum likelihood localization of multiple sources by alternating projection”, IEEE Trans. Signal Processing, vol. 36, pp. 1553-1560, 1988
[14] M. D. Austin and G. L. Stuber, “In-service signal quality estimation for TDMA cellular systems”, IEEE Personal Indoor and Mobile Radio Comm., vol. 2, pp. 836-840, 1995
[15] C. W Wang, L. C. Wang, “Signal to interference ratio measurement techniques for CDMA cellular systems in a frequency-selective multipath fading channel”, IEEE Wireless Commun., pp. 34-37, 2001