臺灣博碩士論文加值系統

在過去十年間，直序分碼多工進接系統被廣泛研究討論。並且被選為第三代行動通訊系統中的規格之一。
在直序分碼多工進接系統中，傳統接收器效能受限於兩個主要因素：多工干擾和遠近效應。為了解決這兩個問題，干擾抑制技術和功率控制演算法被廣泛地討論著。Ulukus與Yates提出了結合最小均方差干擾抑制及功率控制技術的方法，稱為最小均方差功率控制技術。此法有優異的效能，但有較高的複雜度。在本論文中，為了減低運算複雜度，我們使用適應性干擾抑制取代原本架構中估計濾波器係數的最小均方差演算法。另一方面，大部份通訊系統都有採用錯誤更正碼來提昇系統的效能。我們採用渦輪編碼，並將解碼器的輸出傳回到適應性干擾抑制演算法中。在此，我們利用Turbo Principle的觀念，藉由系統中不同方塊間訊息的互相傳遞交換，進而改善系統整體的效能。
從電腦模擬的結果，我們可以發現所提出的架構可以降低傳送所需的功率與提供更準確地訊號與雜訊比。以適應性干擾抑制技術取代最小均方差干擾抑制技術，其穩態效能與最小均方差干擾抑制技術相當。

Direct sequence code-division multiple-access (DS-CDMA) has been widely investigated over the past decade and has been chosen as the air interface technique for the third generation mobile communication systems.
It is well known that the capacity of the conventional receiver in the CDMA systems is limited by the multiple access interference and the near-far effect. There are two solutions to these two problems: power control and multiuser detection. In this thesis, power control and various interference suppression algorithms are studied. Ulukus and Yates proposed an algorithm which combines the minimum mean square error (MMSE) interference suppression and power control. This algorithm exhibits impressive performance; however, it involves high complexity in computing the filter coefficients. In this thesis, we use adaptive algorithms to replace the instantaneous MMSE algorithm in interference suppression for complexity reduction. We then propose a power control scheme with adaptive interference suppression for turbo coded DS-CDMA systems. Moreover, we propose a modified power control with MMSE interference suppression scheme, which performs pre-cancellation of the interference by using the soft information from the turbo decoders’ outputs, to further reduce the interference. Computer simulation results show that the modified scheme can achieve efficient power control in a DS-CDMA system.

Abstract……………………………………………………………………i
Contents……………………………………………………………………ii
List of Figures......................................................iv
List of Tables.......................................................vi
Chapter 1 Introduction…………………………………………………1
1.1 Introduction to CDMA Systems……………………………1
1.2 Limitation Factors of the CDMA Systems…………………………2
1.3 Mitigation of MAI and the Near-Far Problem………………3
1.4 Thesis Outline………………………………………………………………4
Chapter 2 Interference Suppression and Power Control…………5
2.1 System Model.........................................................5
2.2 Interference Suppression for DS-CDMA Systems..........................................7
2.2.1 Optimum MMSE Interference Suppression............................................7
2.2.2 The Adaptive LMS Interference Suppression Algorithm.....................10
2.2.3 The Adaptive MOE Interference Suppression Algorithm.....................11
2.3 Power Control Based on SIR Measurement..................................................13
2.4 MMSE Interference Suppression with Power Control..................................15
Chapter 3 A Power Control Scheme with Adaptive Interference Suppression for Turbo-Coded systems....................................................17
3.1 System Model......................................................18
3.2 An Iterative Multiuser Receiver with Power Control....................................................19
3.2.1 SISO Turbo Decoding....................................................20
3.2.2 Soft Interference Suppression ................................................22
3.2.2.1 The Instantaneous MMSE Interference Suppression Algorithm...................................................22
3.2.2.2 Adaptive Constrained LMS Interference Suppression Algorithm...................................................25
3.2.3 Power Control.....................................................26
Chapter 4 Simulation Results.....................................................31
4.1 Simulation Settings....................................................31
4.2 Performance Comparison of Different SIR Estimation Methods.....................................................32
4.3 Performance Comparison of the Uncoded and Coded Systems.....................................................37
4.4 Performance Evaluations for Different Numbers of Iterations..................................................40
4.5 Performance Comparison of the IMMSE, CLMS, and MOE Interference Suppression Schemes with Power Control....................................................42
4.6 Computational Complexity Analysis....................................................45
Chapter 5 Conclusions.................................................47
5.1 Thesis Summary.....................................................47
5.2 Future Work.........................................................48
References...................................................49

[1] T. Ojanperä and R. Prasad, Wideband CDMA for Third Generation Mobile Communications. Norwood, MA: Artech House , 1998.
[2] A. J. Viterbi, CDMA: Principles of Spread Spectrum Communication. Reading, MA: Addison-Wesley, 1995.
[3] S. Verdu, “Minimum probability of error for asynchronous Gaussian multiple access channel,” IEEE Trans. Inform. Theory, vol. IT-32, pp.85-96, Jan. 1986.
[4] R. Lupas and S. Verdu, “ Linear multiuser detectors for asynchronous code-division multiple-access channels,” IEEE Trans. Inform. Theory, vol. 35, pp 123-136, Jan. 1989.
[5] A. Duel-Hallen, “Decorrelating decision-feedback multiuser detector for synchronous code-division multiple-access channel,” IEEE Trans. Communications, vol. 41, pp 285-290, Feb. 1993.
[6] U. Madhow and M. L. Honig, “Error probability and near-far resistance of minimum mean square error interference suppression schemes for CDMA,” in Proc. 1992 IEEE Globecom Conf. (GLOBECOM ’92), 1992, pp. 1339-1343.
[7] U. Madhow and M. L. Hoing, “ MMSE interference suppression for direct-sequence spread spectrum CDMA,” IEEE Trans. Commun., vol. 42, pp. 3178-3188, Dec. 1994.
[8] S. Ulukus and R. D. Yates, “Stochastic power control for cellular radio systems,” IEEE Trans. Commun., vol. 46, pp. 784-798, June 1998