臺灣博碩士論文加值系統

近幾年來，相較於分時多工存取系統(TDMA)有較高容量、能抵抗多重路徑之衰減等許多優點之分碼多工存取系統(CDMA)成為一重要之通訊機制，已成為實現3G無線網路系統基本的方法。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。
現在已有一些通道估測的方法被提出，如利用最小平方法(least-square procedure)和適應性最陡坡降回歸法則(steepest-descent recursive adaptation)所提出之通道估測。本文將提出一個結合此通道估測方法與可用來估測用戶功率大小的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，我們不須知道用戶傳送功率與傳送通道函數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的更合乎實際上的通訊狀況。經過模擬驗證，此接收器的效能仍然維持在不錯的範圍內。

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.
Some channel estimation methods have been proposed now, e.g. the channel estimation by least-square method and steepest-descent recursive adaptation rule. In this thesis, an interference cancellation receiver incorporating the channel estimation method and the interference projection method to estimate the power of users is introduced. Compared to original interference cancellation receiver, we can demodulate the information signal under the unknown power of users and channel functions. So, the receiver we proposed is clearly more fit the practical communication situation. After the simulation, this receiver can still hold a good performance.

Contents

List of Figures

Chapter 1 Introduction
1.1 Motivation
1.2 Thesis Organization

Chapter 2 Spread Spectrum and CDMA System
2.1 Direct Sequence Spread Spectrum
2.2 CDMA System

Chapter 3 PIC Structure Receiver with Amplitude and Channel Estimation
3.1 Amplitude Estimation
3.1.1 System Model
3.1.2 Training Mode
3.2 Channel Estimation
3.2.1 System Model
3.2.2 Channel estimation algorithm
3.3 PIC Receiver

Chapter 4 Simulations and Discussions
4.1 Simulation Parameters
4.2 Performance Analysis

Chapter 5 Conclusions and Suggestions
5.1 Conclusions
5.2 Suggestions

References

Appendix




















List of Figures

Figure 2.1 BPSK DSSS transmitter and receiver 4
Figure 2.2 BPSK DSSS spreading and despreading 6
Figure 2.3 Power spectrum density of DSSS signal: (a) information signal (b) after spreading (c) despreading signal 6

Figure 2.4 Multiple access schemes: (a) FDMA (b) TDMA (c) CDMA 7
Figure 4.1 Performance of the channel estimation recursive adaptive algorithm. System parameter , . 34

Figure 4.2 Performance comparison : BER of user 1 v.s. with and users 35

Figure 4.3 Performance comparison : BER of user 1 v.s. with and users 35

Figure 4.4 Performance comparison : BER of user 1 v.s. with and users 36

Figure 4.5 Performance comparison : BER of user 1 v.s. with and users 36

Figure 4.6 Performance comparison : BER of user 1 v.s. with and users 37

Figure 4.7 Performance comparison : BER of user 1 v.s. with and users 37

Figure 4.8 Performance comparison : BER of user 1 v.s. with and users 38

Figure 4.9 Performance comparison : BER of user 1 v.s. with and users 38

Figure 4.10 Performance comparison : BER of user 1 v.s. with and users 39

Figure 4.11 Performance comparison : BER of user 1 v.s. with and users 39

Figure 4.12 Performance comparison : BER of user 1 v.s. with and users 40

Figure 4.13 Performance comparison : BER of user 1 v.s. with and users 40

Figure 4.14 Performance comparison : BER of user 1 v.s. with and users 41

Figure 4.15 Performance comparison : BER of user 1 v.s. with and users 41

Figure 4.16 Performance comparison : BER of user 1 v.s. with and users 42

Figure 4.17 Performance comparison : BER of user 1 v.s. with and users 42

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