臺灣博碩士論文加值系統

本論文主要是研究超寬頻(Ultra-WideBand, UWB)系統之多用戶檢測器。在多用戶傳送的環境下，因為多重存取干擾(multiple access interference)的效應而導致系統性能的降低。為了有效抑制多重存取的干擾，我們採用H.V. Poor所提出來的子空間估計之盲蔽式適應性多用戶檢測器。除此之外，必需考量到超寬頻系統在室內環境下的運作，將導致多路徑效應而造成嚴重的碼際干擾(inter-symbol interference)。為了改善碼際干擾的問題，我們使用Rake接收器藉此降低多路徑效應的影響，進而提升系統的性能。
此外我們考慮移動性超寬頻系統的收發器。當收發器的傳送位置改變，會造成不同通道模式的影響，導致我們所採用的子空間估計的盲蔽式適應性多用戶檢測器無法即時適應系統的瞬間改變而導致性能降低、收斂速度變慢。為了克服這樣的問題，我們提出一個低複雜度的判斷機制，稱之為決策瞬間時間(decision timing instant)。最後，模擬結果將證實我們提出的機制可以有效的偵測出環境瞬間的變動，並且改進在時變通道中的盲蔽式適應性多用戶檢測器。

In this thesis, we will focus on the multiuser detection of UWB systems. In the multiuser transmission environment, multiple access interference (MAI) becomes a serious issue and results in the degradation of system performance. To efficiently suppress MAI, a subspace-based blind adaptive linear detector which was first proposed by H.V. Poor is chosen. Besides, since the UWB system is mainly operated in an indoor environment, it also causes a serious inter-symbol interference (ISI). Therefore, the Rake receiver is adopted in this thesis to mitigate the multipath distortion.
In addition, we consider a mobile UWB transceiver. Changing the transmission position will sometimes suffer the transition of the channel models because of different transmission distance or characteristics. However, the subspace-based blind adaptive linear detector proposed by H. V. Poor is highly sensitive to the sudden change of the channel environment over a time-varying channel, eventually results in a large performance degradation and a slow convergence speed to the steady state. In order to overcome this shortcoming, we propose a low complexity decision mechanism, termed the decision timing instant (DTI). Simulation results show that DTI is able to fast and precisely trace the variation of the channel environment and to improve the performance of the blind adaptive multiuser detection with a subspace approach over time-varying channels.

摘要 ..............................................................i
Abstract .........................................................ii
Contents .........................................................iv
List of Tables ...................................................vi
List of Figures ..................................................vii
Chapter 1 Introduction ...........................................1
1.1 Background Overview and Motivation
1.2 Organization
Chapter 2 Multiuser Receiver for TH-UWB Systems over Multipath
Fading Channels .........................................4
2.1 Introduction to Ultra Wide-Band Systems
2.2 UWB Multipath Channel Model
2.3 RAKE Receivers
2.4 System Model
Chapter 3 Blind Multiuser Detection under UWB Channel Model ......18
3.1 Subspace Concept
3.2 Subspace-Based Linear Multiuser Detectors
3.3 Tracking the Signal Subspace
3.4 Simulation under UWB Channel Model
Chapter 4 Subspace-based Blind Adaptive Multi-user Detectors over
Time-Varying Multipath Channels ........................35
4.1 Introduction
4.2 Design of Decision Timing Instant
4.3 Simulation and Discussion
Chapter 5 Conclusions ............................................49
References .......................................................51

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