臺灣博碩士論文加值系統

毫微微細胞 (Femtocell) 被視為下世代無線系統的重要技術。因為毫微微細胞可以利用較低的傳輸功率 (Transmit Power) 及生產成本達到有效改善無線通訊於室內環境的資料傳輸速率 (Data Transmission Rate) 與信號涵蓋範圍 (Signal Coverage)。然而，當毫微微細胞系統被廣泛應用的時候，蜂巢式巨細胞基地台 (Macrocell) 及其他毫微微細胞對毫微微細胞的干擾影響甚巨。這種複雜的異質跨層干擾 (Two-tier Interference) 則成為不可忽視的因素。因此，當我們面對這個問題時，如何設計一個自主式及分散式的通道選取機制來克服異質跨層干擾將會是一項挑戰。在此論文中，我們針對正交分頻多工存取 (Orthogonal Frequency Division Multiple Access, OFDMA)之毫微微細胞系統，提出分散式通道選取機制以減少干擾、並提升傳輸速率及信號可靠度 (Link Reliability)。我們提出通道增益導向之通道選取機制(Gain-oriented Subchannel Selection Scheme) 及干擾避免導向之通道選取機制 (Interference-Avoidance Oriented Subchannel Selection Scheme)。經由模擬的結果顯示，來自巨細胞及其它毫微微細胞的干擾對於傳輸速率及信號可靠度有極大的影響。藉由適當調整傳輸的子通道數量 (Channel Usage Ratio)，我們所提出來的分散式通道選取機制可以顯著改善傳輸速率及信號可靠度。
此外，我們在論文中也針對毫微微細胞系統，分析異質跨層干擾影響。經由數學推導，在已知鄰近毫微微細胞基地台及巨細胞基地台位置與屏蔽效應的影響 (Shadowing Standard Deviation)，我們可以估算出毫微微細胞使用者的信號可靠度。同時我們也可以分析毫微微細胞的通道使用率及可適用之巨細胞的半徑範圍。
最後我們探討當毫微微細胞系統使用時，如何同時尋找適當傳輸功率與子通道使用率的共同設計法則。我們比較『通道控制優先』與『功率控制優先』這兩種法則。雖然兩種法則皆可以找到適當的傳輸功率與通道使用率以提供最大功率效益。然而，經由模擬測試，我們發現『通道使用比例控制優先法則』比『功率控制優先法則』可以用更少的調整次數來找到適當的傳輸功率與子通道使用率以滿足最大能量效益。因為通道控制的影響比起功率控制的影響有所不同，通道使用比例控制可以視為對全部資源的巨觀分配法則，功率控制則是針對所分配資源的微觀使用法則。
總體而言，本論文之貢獻包括下列三項：
• 分散式通道選取機制：使毫微微細胞可以依據不同毫微微細胞的佈建密度與巨細胞距離的遠近提供適當的通道選取機制。且針對所在區域室外使用者出現的頻率給予毫微微細胞與蜂巢式巨細胞是否使用相同頻段之建議。
• 信號可靠度的分析架構：藉由毫微微細胞所處的環境分析其使用者信號可靠度的數學方法，並藉由模擬驗證。
• 傳輸功率與通道使用率的選取流程：針對毫微微細胞開機後如何找到適用的傳輸功率與通道使用率不僅可以維持毫微微細胞使用者傳輸速率與信號可靠度並滿足最大功率效益。
綜合以上，從毫微微細胞系統剛開機時，該如何找到適用的傳輸功率與通道使用率開始，至開機完成後，該以何種方式選取通道，本論文皆提出相關的共同設計法則與選取機制，本篇論文所討論之議題可以供未來毫微微細胞系統設計及佈建法則的重要參考。

摘要. . . . . . . . . . . .. . . . . . . . . . . . .VI
Abstract . . . . . . . . . . . . .. . . . . . . . .VIII
Acknowledgements . . . . . . . . . . . . . . . . . . . .X
List of Tables . . . . . . . . . . . . . . . . . . . .XVI
List of Figures . . . . . . . . . . . . . . . . . . XVIII
1 Introduction . . . . . . . . . . . . . . . . . . . ..1
1.1 Problem and Solution . . . . . . . . . . . . . . . 1
1.1.1 Distributed Channel Selection Principle for Femtocell with Two-tier Interference. . . . . . . . . . . . . . . . 2
1.1.2 Analysis the Outage Probability of OFDMA-based Femtocell . .. . . . . . . . . . . . . . . . . . . . . .2
1.1.3 The Joint Sub-carrier Allocation and Power Control for Maxi-mizing Energy Efficiency in OFDMA Based Femtocells.3
1.2 Thesis Outline . . . . . . . . . . . . . . . . . . . . 3
2 Background . . . . . . . . . . . . . . . . . . . . . . .5
2.1 Femtocell . . . . . . . . . . . . . . . . . . . . . . 5
2.1.1 The Concept of Femtocell . . . . . . . . . . . . . . 5
2.1.2 Femtocell Subscription Types . . . . . . . . . . . . 6
2.2 Orthogonal Frequency Division Multiple Access . . . . .7
2.2.1 Basic Principle . . . . . . . . . . . . . . . . . . 7
2.2.2 Sub-carrier Permutation . . . . . . . . . . . . . . 9
2.2.3 IEEE 802.16m WiMAX System . . . . . . . . . . . . . 9
2.2.4 3GPP Long Term Evolution (LTE) . . . . . . . . . . 12
2.3 Literature Survey . . . . . . . . . . . . . . . . . . 14
2.3.1 Distributed Channel Selection Principle for Femtocell with Two-tier Interference . . . . . . . . . . . . . . . 14
2.3.2 Outage Probability Analysis for OFDMA-based Femtocell . . . . . . . . . . .. . . . . . . . . . . . . .14
2.3.3 The Joint Sub-carrier Allocation and Power Control for Maximizing Energy Efficiency in OFDMA-Based Femtocells . . . . . . .. . . . . . . . . . . . . . . . . 15
3 System Models . . . . . . . . . . . . . . . . . . . . .16
3.1 System Architecture . . . . . . . . . . . . . . . . . 16
3.1.1 Location-Aware Femtocells . . . . . . . . . . . . . 17
3.2 Radio Channel Effects . . . . . . . . . . . . . . . . 20
3.3 Exponential Effective SINR Mapping (EESM) . . . . . . 21
3.4 Performance Metrics . . . . . .. . . . . . . . . . . 24
3.4.1 Link Reliability . . . . . . . . . . . . . . . . . 24
3.4.2 Femtocell Capacity . . . . . .. . . . . . . . . . . 24
3.4.3 Effective Spectrum Efficiency . . . . . . . . . . . . 25
4 Distributed Channel Selection for Femtocell with Two-tier Interference . . . . . . . . . . . . . .. . . . . . . . . 27
4.1 Femtocell Capacity Maximization . . . . . . . . . . . 27
4.2 Distributed Channel Selection Scheme . . . . . . . . 28
4.2.1 Max-Min Gain-Oriented Subchannel Selection Scheme . 28
4.2.2 Max-Avg Gain-Oriented Subchannel Selection Scheme . 29
4.2.3 Min-Max Interference Avoidance Subchannel Selection Scheme . . . . . . . . . . . . . . . . . . . . . . . . . .30
4.2.4 Min-Avg Interference Avoidance Subchannel Selection Scheme . . . . . . . . . . . . . . . . . . . . . . . . . .30
4.3 Simulation Results . . . . . . . . . . . . . . . . . 31
4.3.1 Link Reliability and Capacity in Exclusive Spectrum Allocation . . . . . . . . . . . . . . .. . . . . . . . .33
4.3.2 Link Reliability and Capacity in Shared Spectrum Allocation . . . . . . . . . . . . . . . . . . . . . . . 34
4.3.3 Spectrum Efficiency Improvement by Location Awareness . . .. . . . . . . . . . . . . . . . . . . . 38
4.3.4 Impacts of Location Awareness on Spectrum Efficiency . . . . . . . . . . . . . . . . . . . . . . 42
4.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . 45
5 Analysis of Distributed Channel Selection for Femtocell with Two-tier Interference: Single Carrier Case . . . . . 49
5.1 Assumptions . . . . . . . . . . . . . . . . . . . . . 49
5.1.1 Sub-carrier Allocation . . . . .. . . . . . . . . . 49
5.1.2 Radio Channel . . . . . . . . . . . . . . . . . . 50
5.1.3 Signal to Interference and Noise Ratio . . . . . . 51
5.2 Outage Probability of Single Femtocell . . . . .. . . 52
5.3 Outage Probability of Random Channel Selection Principle for Femtocell with Two-tier Interference . . . 53
5.4 Outage Probability of Gain-Oriented Channel Selection Principle for Femtocell with Two-tier Interference . . . 54
5.4.1 Outage Probability of Maximal Link Gain Channel for Femtocell with Two-tier Interference . . . . . . . . . . 55
5.4.2 Outage Probability of n-th Highest Link Gain Channel for Femtocell with Two-tier Interference . . . . . . . . 58
5.5 Simulation Results . . . . . . . . . . . . . . . . . 60
5.5.1 Outage Probability in Exclusive Spectrum Allocation .. . . . . .. . . . . .. . . . . .. . . . . . 60
5.5.2 Outage Probability in Shared Spectrum Allocation . . . . . . . . . . . . . . . . . . . . . . . 61
5.5.3 Impact of Macrocell Radius and Femtocell Channel Usage Ratio . . . . . .. . . . . .. . . . . .. . . . . . .64
6 Analysis of Distributed Channel Selection for Femtocell with Two-tier Interference: Multicarrier Case . . . . . . 72
6.1 Assumptions . . . . . . . . . . . . . . . . . . . . . 72
6.1.1 Sub-carrier Allocation . . . . . . .. . . . . . . . 72
6.1.2 Radio Channel . . . . . . . . . .. . . . . . . . . 73
6.1.3 Signal to Interference and Noise Ratio . . . . . . 73
6.2 Outage Probability of Single Femtocell . .. . . . . . 75
6.3 Outage Probability of Random Channel Selection Principle for Femtocell with Two-tier Interference . . . 76
6.3.1 Single Interference Case for Random Channel Selection Principle . . . .. . . . . . . . . . . . . . . . . . . .76
6.3.2 Multi-interference Case for Random Channel Selection Principle . . . . . . . . . . . . . . . . . . . . . . . 77
6.4 Outage Probability of Gain-Oriented Channel Selection Principle for Femtocell with Two-tier Interference .. . . 79
6.4.1 Outage Probability of Maximal Link Gain Channel for Femtocell with Two-tier Interference . . . . . . . . . . 79
6.4.2 Outage Probability of n-th Highest Link Gain Channel for Femtocell with Two-tier Interference . . . . . . . . 83
6.5 Simulation Results . . . . . . . . . . . . . . . . . 88
6.5.1 Outage Probability in Exclusive Spectrum Allocation . . . . . . . . . . . . . . . . . . . . . . . 88
6.5.2 Outage Probability in Shared Spectrum Allocation . . . . . . . . . . . . . . . . . . . . . . . 89
6.5.3 Impact of Macrocell Radius and Femtocell Channel Usage Ratio . . . . . . . . . . . . . . . . . . . . . . .92
7 Joint Sub-carrier Allocation and Power Control for Maximizing Energy Efficiency in OFDMA Based Femtocells. . 100
7.1 Introduction . . . . . . . . . . . . . . . . . . . . 100
7.2 Problem Formulation . . . . . . . . . . . . . . . . 101
7.3 Joint Sub-carrier Allocation and Power Control Principles . . . . . . . . . . . . . . . . . . . . . . . 103
7.3.1 Impacts of transmission power on energy efficiency .103
7.3.2 Impacts of channel usage ratio on energy efficiency . . . . . . . . . . . . . . . . . . . . . . . 103
7.3.3 Joint Sub-carrier Allocation and Power Control principle . . . . . . . . . . . . . . . . . . . . . . . .104
7.4 Simulation Results . . . . . . . . . . . . . . . . . 108
7.4.1 Capacity in Shared Spectrum Allocation . . . . . . 108
7.4.2 Energy Efficiency in Shared Spectrum Allocation . . 109
7.4.3 Maximal Energy Efficiency in Shared Spectrum Allocation . . . . . . . . . . . . . . . . . . . . . . .109
7.4.4 Impact of Adjusting Channel Usage Ratio First and Transmit Power First on Adjusting Times . .. . . . . . . 113
7.4.5 Improvement of Energy Efficiency . . . . . . . . . .114
8 Conclusions . . . . .. . . . . . . . . . . . . . . . .117
Bibliography . . . . . . . . . . . . . . . . . . . . . .119
Vita . . . . . . . . . . . . . . . . . . . . . . . . . .122

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