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標題: | LTE-A 多點協調傳輸技術之最佳傳輸點選擇 Optimizing Transmission Point Selection for Coordinated Multi-Point Transmission in LTE-Advanced Systems |
作者: | Chun-Yuan Yang 楊淳淵 |
指導教授: | 謝宏昀(Hung-Yun Hsieh) |
關鍵字: | 多點協調傳輸技術, Coordinated Multi-Point, |
出版年 : | 2011 |
學位: | 碩士 |
摘要: | 多點協調傳輸與接收技術(CoMP)是 LTE-Advanced 系統中一項能提升位於 服務邊界使用者的服務品質以增進整體系統效能的技術。雖然理論上該技術能增 加使用者接收信號的品質,然而在實際系統中,多個基地台在共同傳輸前互相做 協調溝通的成本,往往會對系統造成額外的負擔,因而使效能上的增益不如預期。 為了瞭解 CoMP 在現今系統的可行性,並找出其適用情境,我們藉由最佳化工具 的幫助來衡量 CoMP 能為整個網路帶來的最大效益。目標函數的部份,除了一般 傳統在做網路最佳化常考慮到的系統容量之外,我們也從使用者的角度出發,提 出以整個網路裡頭能服務到的使用者個數作為衡量 CoMP 效能的另一個依據。我 們先考慮基本的模型,再將實作 CoMP 會遭遇到的額外負擔考量進來;此外,我 們也利用將限制式做線性轉換以及將目標函數利用分段式線性函數近似這兩個方 法來簡化解決問題的計算複雜度。實驗結果顯示,在最大化系統容量的目標下, 不考慮做 CoMP 的額外負擔時,CoMP 能提升 50% 左右的系統容量;然而,在 將額外負擔納入考量的情況下,使用 CoMP 幾乎沒有增益存在。另一方面,在最 大化系統服務使用者個數的目標下,使用 CoMP 可以使額外 12% 的使用者被服 務到,而且即便是在最嚴重的額外負擔設定下,CoMP 仍然能夠有 6% 左右的增 益;在更進一步的觀察基地台與使用者的服務情形後,我們發現在特定的通道容 量服務品質保障下,使用者會偏好由多個信號強度相當的基地台共同服務,而不 會選擇只給自己原本所屬的基地台做一對一服務。經由我們的分析發現即便 CoMP 的額外負擔對系統容量的增益影響甚巨,但在服務使用者的個數上仍能有 所提升;換句話說,在最佳的基地台與使用者服務分配下,CoMP 可以有效地提 升使用者被服務到的機率。 Coordinated multiple point transmission, referred to CoMP, is one of the new features in LTE-Advanced specification and a promising technique to improve both the throughput of UEs at cell edge and overall system performance. However, coordinations among base stations incur overheads in CoMP utilization which varies depending on how many and which transmission points are involved. In this thesis, we investigate the optimal transmission points allocation problem in CoMP with the aid of the network optimization tools. To enhance UEs' service probability, we consider the goal of maximizing the number of served UEs with satisfied QoS requirement in addition to the conventional approach which aims at maximization of the network sum capacity. We first model the basic form of those problems, and then introduce linearization transformation for constraints and linear approximation for the objective to reduce complexity. Finally we model additional overheads in CoMP as utilization penalty into our formulations. Evaluations show that CoMP can bring 12% more served UEs and 50% more sum capacity for those UEs suffered from severe interference. Moreover, we observe that for certain QoS requirements, UEs should ideally be served by multiple transmission points with comparable signal strengths rather than by its serving base station with full power consumption. Our results also reveal that typically a UE will be served by at most two transmission points in situations where CoMP obtains performance gain over single cell transmission. When signaling overhead is considered, the performance of CoMP based on sum capacity maximization degrades to that of the single cell transmission scheme, where no UE chooses to be served through CoMP scheme. CoMP based on UE number maximization, on the other hand, can still achieve a 6% gain even under the highest overheads. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/33629 |
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顯示於系所單位: | 電信工程學研究所 |
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