目前普遍上所使用的行動通訊系統必須要擁有多方面的服務，例如：聲音，影像，資料的傳輸。因此用戶端可能會以不同的傳輸速率來傳送訊號。在此論文中，我們提出兩種調變方法，MC跟MPG的技術，配合直序(direct sequence)展頻技術調變之分碼多工存取系統來實行多速率傳輸。
另外，由於使用分碼多工系統最主要的缺點是會有多重存取干擾(MAI)，因為在系統中，多位使用者同時使用了相同的頻帶來傳輸訊息。這些干擾會降低系統之效能。因此本論文使用了並列干擾消除偵測器(PIC)，利用一層層的疊代，改善傳統匹配濾波器(matched filter)的效能，有效抑制干擾。但要能有效利用平行干擾消除偵測器必須配合干擾投影法估測出每個使用者的傳輸振幅。
此外在傳輸訊號的過程當中，受到多重路徑影響的關係，因此接收端接收訊號時會收到不同時間延遲、不同通道振幅衰減的加成訊號，這會使得解調還原工作變的困難。因此本文提出一個能同時估測通道數目及延遲時間的方法。並將所估測通道數目及延遲時間的資料，配合原來平行干擾消除偵測器，以得到一個更合乎實際狀況之接收器。
最後我們結合多速率系統及具有通道延遲與通道數估測的平行干擾消除偵測器，並觀察數據模擬的情形，分別討論MC及MPG系統在不同通道延遲與數目偵測下的效能。

Recently, the popular mobile communication systems are expected to support several kinds of service, like voice, video, and data transmission. Hence, the users may transmit their signal in different data rates. In this thesis, we introduce two kinds of accessing method, MC access and MPG access, and choose Code Division Multiple Access (CDMA) by use of direct-sequence spread spectrum (DSSS) to demodulate a multi-rate system.
Besides, the most important shortcomings of CDMA system is the multiple access interference (MAI). The multiple access interference is produced because there are multiple users using the same frequency band simultaneously. This interference will degrade the performance of the system. Hence, in order to suppress the interference, the parallel interference cancellation (PIC) scheme is proposed in this thesis. This scheme uses the adaptive iteration to improve the performance of receiver. By using the PIC scheme, the interference projection method is introduced to estimate the transmitting amplitude for every user.
During signal transmission, the receiver will receive many replicas of the transmitted signal with slightly time difference and amplitude decay because of the multi-path fading. This may cause the difficulty in demodulating the received signal. A method which can estimate path numbers and delay time simultaneously is introduced in this thesis. We can use this information together with the PIC scheme to obtain a more practical communication receiver.
Finally, the multi-rate system using PIC scheme with path and delay estimator are discussed. Some results of simulation are given at last to illustrate the performance of MC and MPG system, and the performance of path and delay estimator.

[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]
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
[4]
D. Divsalar, M. Simon, and D. Raphaeli, “Improved parallel interference cancellation for CDMA”, IEEE Trans. on Commun., vol. 46, pp. 258-268, 1998
[5] 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
[6] 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
[7] Markku J. Juntti and Jorma O. Lilleberg, “Linear FIR multiuser detection for multiple data rate CDMA systems”, in Proc. IEEE Vehic. Tech. Conf., vol. 2, pp. 455-459, 1997
[8] Markku J. Juntti, “System concept comparisons for multirate CDMA with multiuser detection”, in Proc. IEEE Vehic. Tech. Conf., vol. 1, pp. 36-40, 1998
[9] Zihua GUO and Khaled Ben Letaief, “Performance of VSG-CDMA and MC-CDMA in multirate systems”, in Proc. IEEE Vehic. Tech. Conf., vol. 1, pp. 501-505, 2001
[10] A. F. van Meeteren, T. Ojanpera, H. Nikookar, and R. Prasad, “Groupwise weighted parallel interference cancellation for asynchronous multirate DS-CDMA”, in Proc. IEEE Vehic. Tech. Conf., vol. 3, pp. 1820-1824, 1999
[11] Matti Latva-aho., Jorma Lilleberg, “Parallel interference cancellation in multiuser CDMA Channel Estimation”, Kluwer Academic, Wireless Personal Commun., vol. 7, pp. 171-195, 1998
[12] T. S. Rappaport, “Wireless communications: principles and practice”, Prentice Hall 2nd edition, 2002
[13] Simon Haykin, “Communication Systems”, Wiley, 2001
[14] John G. Proakis, “Digital communications”, Mc Graw Hill, 4th edition, 2001.
[15] Jianfeng Weng, Guoqiang Xue, Tho Le-Ngoc, and Sofiene Tahar, “Multistage Interference Cancellation with Diversity Reception for Asynchronous QPSK DS/CDMA Systems over Multipath Fading Channels”, IEEE Journal on Selected Areas in Commun., vol. 17, pp. 2162-2180, 1999
[16] I. Ziskind, M. Wax, “Maximum likelihood localization of multiple sources by alternating projection”, IEEE Trans. Signal Processing, vol. 36, pp. 1553-1560, 1988
[17] R.A. Iltis, “Exact and approximate maximum-likelihood parameter estimation for quasi-synchronous CDMA signals”, IEEE Trans. Commun., vol. 48, pp. 1208-1216, 2000
[18] 楊翔策, “具延遲與傳輸功率估測之PIC架構CDMA多用戶偵測器”, 國立清華大學碩士論文, 九十六年六月

[19] 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
[20]
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
[21]
黃裕程, “具PIC偵測器之多速率多路徑直序展頻分碼多工存取系統”, 國立清華大學碩士論文, 九十七年六月