臺灣博碩士論文加值系統

在下行二維展頻多載波直接序列碼分碼多重接取系統中，同時維持服務品質要求及消除干擾是一件重要且困難的工作。為了達到此目標，我們首先整合功率控制機制及干擾消除選碼策略。在這整合策略中，透過干擾消除選碼策略以消除干擾和利用功率控制以維持服務品質。為了簡化選碼策略，藉由效能分析我們定義一個以功率控制為基礎的MAI係數。感謝功率控制為基礎的MAI係數的幫助，藉由預測選碼可能產生的干擾量，我們可以評估每個候選碼。透過此項干擾預估，系統中額外的MAI 可以被避免。模擬結果顯示在我們考慮的情況下，此整合策略可以維持預定的信號品質且改善碼允許率4％，同時減少功率消耗達19％。在用戶來來往往的期間，為了維持低干擾碼樹結構，我們整合第一部份的選碼策略並提出換碼機制。經由模擬結果顯示此換碼策略可以有效低改善碼中斷機率及碼存活率。

Maintaining the quality-of-service (QoS) requirement while eliminating interference is an important but difficult task in the downlink multi-carrier direct sequence code division multiple access (MC-DS-CDMA) with two-dimensional (2D) spreading. To achieve this goal, we firstly integrate the power control (PC) mechanism and the interference avoidance code assignment strategy. This joint policy is to eliminate interference via an interference avoidance (IA) code assignment strategy and then maintain the QoS via a power control mechanism. To facilitate the code assignment strategy, by performance analysis, we define a new PC-based multiple access interference (MAI)coefficient. Thanks to the help of the PC-based MAI coefficient, we can evaluate each candidate code by quantitatively predicting the interference a possible code assignment may produce. With this interference pre-evaluation, the extra MAI in the system can be avoided. Subsequently, the power control mechanism can maintain the QoS using less power to further eliminate MAI. The simulation results show that the proposed joint scheme can maintain a predefined signal quality and improve the code admission rate by 4% while reducing the power consumption by 19% in the considered case. Secondly, for the purpose of maintaining a code tree with less interference when users are coming and going, we incorporate the code reassignment strategy into the joint PC and IA code assignment strategy in the first part. The simulation results show that the MC-DS-CDMA with 2D spreading benefits by the code reassignment in terms of call outage probability and code survival rate.

Abstract i
Acknowledgements ii
List of Tables v
List of Figures vi
Glossary of Symbols viii
1 Introduction 1
1.1 Problem Formulation and Solution . . . . . . . . . . . . . . . . . . . . . . 2
1.1.1 A Joint Power Control and Interference Avoidance Code Assignment
Strategy for MC-DS-CDMA with 2D Spreading . . . . . . . . 2
1.1.2 An Interference Avoidance Code Reassignment Strategy for the
Power-Controlled MC-DS-CDMA with 2D Spreading . . . . . . . . 3
1.2 Thesis Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 Background and Literature Survey 5
2.1 Literature Survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.1 QoS Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.2 MAI Elimination . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2.1 Power Control Mechanism . . . . . . . . . . . . . . . . . . . . . . . 6
2.2.2 Two-Dimensional OVSF Code Tree . . . . . . . . . . . . . . . . . . 7
2.2.3 Grid Representation of a 2-D Code Tree . . . . . . . . . . . . . . . 9
3 A Joint Power Control and Interference Avoidance Code Assignment Strategy
for MC-DS-CDMA with 2D Spreading 13
3.1 Motivation and Problem Formulation . . . . . . . . . . . . . . . . . . . . . 13
3.2 System Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.2.1 Transmitted Signal . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.2.2 Received Signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.2.3 Signal-to-Interference and Noise Ratio (SINR) . . . . . . . . . . . . 18
3.3 Optimization of Power Control Mechanism . . . . . . . . . . . . . . . . . . 20
3.4 The Impact of PC on the MAI Coefficient . . . . . . . . . . . . . . . . . . 25
3.5 A Joint PC and Interference Avoidance Code Assignment Strategy . . . . 27
3.5.1 Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.5.2 Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.6 Simulation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.6.1 Simulation Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.6.2 Performnace Comparision of Joint Power Allocation and Code Assignment
Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.7 Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
4 An Interference Avoidance Code Reassignment Strategy for the power-controlled
MC-DS-CDMA with 2D Spreading 42
4.1 Motivation and Problem Formulation . . . . . . . . . . . . . . . . . . . . . 42
4.2 A Joint PC and IA Code Assignment/Reassignment Strategy . . . . . . . . 44
4.3 Simulation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
4.4 Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
5 Concluding Remarks 50
5.1 A Joint Power Control and Interference Avoidance Code Assignment and
Reassignment Strategy for Downlink MC-DS-CDMA with 2D Spreading . 50
5.2 Suggestions for Future Research . . . . . . . . . . . . . . . . . . . . . . . . 51
APPENDIX A 52
Bibliography 54
Vita 58

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