臺灣博碩士論文加值系統

本篇論文中，吾人利用智慧型天線(smart antenna)的技術來增進無線行動通訊
系統的容量並且克服它在實際應用時會遭遇的問題，即同時會有快速雷利衰減(fast
Rayleigh fading)、頻率選擇性衰減(frequency selective fading)及共通
道干擾(co-channel interference)的出現。不同於傳統運用波束成形
(beam-forming)的方式來調整陣列的權重係數(weights)以符合波束的形式
(beam pattern)；吾人由空間分割上的組合概念著手，並且利用它延展出時間-空間
處理法來對抗如此困頓的情形。

在此吾人提出利用可適性時間-空間陣列天線組合之方法，來減低多路徑衰減
(multipath fading)對想得到之訊號(desired signal)的影響，並且排除其他
訊號之干擾。在實驗中，一已知簡短的訓練碼(training sequence)遞迴性地藉由
RLS運算法來決定時間-空間處理法初始的權重係數，而在隨後的資料傳輸時，則使用
直接判斷法(decision-directed mode)則來保持對通道變化的追蹤。所謂時間-空間
處理法的架構是由一連串T/2時間間隔分布的TDL (tapped delay line)濾波器在
各天線之加成所組成，其後並可選擇性的附加一T時間間隔分布的DFE (decision
feedback equalizer)。正如同吾人所期盼的，這種架構的表現比只有T時間間隔分
布的來得好，並且對於取樣時間的誤差較不敏感。再者，吾人還探討了多使用者
(muiti-users)在同一時間同一頻帶上的偵測問題，在這種情況下，吾人提出了一種
共通道干擾消除法，先估測它然後再加以消除。

In this thesis, we consider the problems of wireless mobile
communication system under the difficult situation like
combined realistic fast Rayleigh fading, frequency selective
channel and the presence of co-channel interference (CCI) by
using smart antenna technique to improve both the performance
and capacity. In contrary to the conventional digital beam-
forming technique which adjusts the array weighting to specify
the beam pattern, our approach follows the concept of spatial
diversity combination and extends it to space-time processing
(STP) for dealing with such difficult cases.

The proposed method uses the adaptive spatial and temporal
combining antenna array to combat frequency selective fast
fading and suppress CCI. A short known training sequence is
used for determining the space-time processor weights
periodically by a RLS algorithm and decision-directed mode is
used to keep track of channel variation during data
transmission. The STP structure used is a sum of T/2-spaced
tapped delay line filters following after the antennas, then
connected with an optional T-spaced decision-feedback filter.
As expected, this structure behaves better than T-spaced STP
and is also insensitive to the timing phase error.
Furthermore, we also formulate the multi-user detection
problem where multiple signals of interest are transmitted
on the same frequency band and to be detected at the same time.
In such a case, we present a STP technique, which incorporates
a CCI cancellation method to predict the CCI and cancel it.

Chinese AbstractⅠ

English AbstractⅡ

AcknowledgementsⅢ

Table of ContentsⅣ

List of FiguresⅥ

List of TablesⅧ

GlossaryⅨ


CHAPTER 1INTRODUCTION1

CHAPTER 2WIRELESS PROPAGATION CHARACTERISTICS AND 5
SPATIAL-TEMPORAL SIGNAL PROCESSING

2.1 Impairments of Wireless Communication Systems5
2.1.1 Multipath Fading5
2.1.2 Delay Spread7
2.1.3 Co-channel Interference8

2.2 Some Existing Methods using Adaptive Smart Antenna Arrays9
2.2.1 Time-Only Processing9
2.2.2 Space-Only Processing10
2.2.3 Space-Time Processing11

CHAPTER 3SPACE AND TIME PROCESSING FOR15
WIRELESS COMMUNICATION

3.1 The System Model of Wireless Communication System with 15
Spatial Diversity

3.2 Time-Domain Only Processing20
3.2.1 Minimum Mean Square Error (MMSE) Linear Equalizer20
3.2.2 Decision-Feedback Equalization22

3.3 The Advantage of Using T/2 Spaced Spatial-Temporal Equalization25
3.3.1 Spatial-Temporal Equalization26
3.3.2 CCI Cancellation29
3.3.3 T/2 Fractionally Spaced Spatial-Temporal Equalization32

CHAPTER 4COMPUTER SIMULATIONS37

4.1 Signal Generation37

4.2 Computer Simulations43
4.2.1 Experiment 1: Performance for different no. of delay spread path41
4.2.2 Experiment 2: Performance for different vehicle speed45
4.2.3 Experiment 3: Performance for different no. of antenna46
4.2.4 Experiment 4: Performance for different vehicle speed with CCI47
4.2.5 Experiment 5: Performance for different SIR48
4.2.6 Experiment 6: CCI reduction by increasing antenna elements49
4.2.7 Experiment 7: CCI reduction by CCI cancellation50
4.2.8 Experiment 8: Effect of sampling time offset51
4.2.9 Experiment 9: Performance for different training length52
4.2.10 Experiment 10: Performance for different length of TDL54

CHAPTER 5CONCLUSIONS58

REFERENCES59

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