臺灣博碩士論文加值系統

　　在分碼多重進接（CDMA）蜂巢式系統中，每一個行動台可同時使用所有的頻率和時槽。因此，同頻干擾量的大小就限制了系統的效能與容量。在CDMA蜂巢式系統中，功率控制是一項用來降低同頻干擾非常重要的技術。功率控制是用以決定最低可能的傳送功率，同時也維持了傳送的信號品質，而使同頻干擾減低到最小的程度。本論文的目的是要分析功率控制多媒體CDMA系統之系統效能。因為在測量功率控制的效能時，信號干擾比（SIR）很廣泛地被用來當作測量的標準，所以這的“多媒體”一詞我們將它定義為多重SIR目標。以OSI網路架構來看，個人行動蜂巢式系統基本上是由實體（Physical）層與媒介存取（MAC）層所組成。在本論文中，我們因此分別針對實體層與媒介存取層來進行功率控制之多媒體CDMA系統的效能分析。
　　我們首先進行多媒體功率控制之效能界限（Performance Bound）的探討。此效能界限值是藉由最佳SIR平衡（SIR-balanced）功率控制連同移除演算法（Removal Algorithm）所得到。接著我們以另一種方法來重新推導這個最佳SIR平衡功率控制方法的下鏈（Downlink）功率控制。電腦模擬顯示出此重新推導出的下鏈功率控制與原本的最佳SIR平衡功率控制方法有相同之下鏈功率控制的效能。然而，這個等效的下鏈功率控制技術比起原本的最佳技術有極低的運算複雜度。利用這個等效的功率控制方法，我們接下來提出一個階層式的功率控制結構來實現原本的最佳功率技術所必需的Eigen-decomposition。並且，分別提出線性預測方法（Linear Prediction Method）與適應性開關策略（Adaptive on-off strategy）來解決不平衡SIR（Unbalanced SIR）與整體中斷（Global Outage）的問題。差分編碼（Differential Coding）則被用以減少傳送功率控制指令所需的位元數。
　　我們接著進行功率控制CDMA系統（3GPP與cdma2000）之實體層的效能分析。分析的結果證明出耙式接收器（Rake Receiver）與功率控制技術在改善CDMA系統效能上確實是必要的。耙式接收器收集多重路徑的信號以達到更好之系統效能。當路徑強度衰減值（Path-strength Decay Factors）為小值的情況下，這樣的多重路徑接收的貢獻是尤其地顯著。即使在不良的功率控制情況下，我們的分析指出具有功率控制的CDMA系統比起不使用功率控制的CDMA系統有更好的系統效能。最後，我們進行不同的功率控制CDMA系統在頻譜重疊的情況下之系統效能影響的評估。所分析之共存的頻譜重疊CDMA系統包含了窄頻的IS-95系統與寬頻的cdma2000系統。從分析的結果發現：覆蓋效能（Overlaid Performance）不但與傳送信號的波形有關，而且也與窄頻IS-95系統的所有用戶如何分佈於整個可用頻帶的情形有密切的關係。這個觀察建議我們要均勻分佈窄頻IS-95的用戶於整個可用之頻帶，以便得到較好的覆蓋效能。

In a code-division multiple access (CDMA) cellular system, all frequency and time resources are allocated to all subscribers simultaneously. Thus, the performance and capacity of such cellular system are mainly limited by cochannel interference. Transmitter power control (TPC) is very important for cellular CDMA systems. It is used to determine the lowest possible power level for maintaining a required signal quality in order to minimize the interference in the system. The objective of this dissertation is to analyze the performance of power-controlled multimedia CDMA systems. The term multimedia, here, is defined as multiple SIR (signal to interference ratio) targets because the concept of SIR is widely used for the performance measure of power control. The mobile cellular system is primarily constituted by physical and MAC layers within the framework of OSI layers. Thus, we would analyze both physical-level and MAC-level performance for power-controlled multimedia CDMA systems in this dissertation.
In the first place, the performance bound for multimedia TPC is investigated. This performance bound is attained from an optimum SIR-balanced TPC together with a removal algorithm. Next, we reformulate the downlink portion of this optimum SIR-balanced TPC in an alternative method. Computer simulations show that the alternative downlink TPC has a performance identical to that of this optimum SIR-balanced TPC. However, the alternative downlink TPC has extremely low complexity as compared to that of the original optimum TPC. Exploiting this alternative TPC, we proposed a hierarchical structure which is feasible for carrying out the eigen-decomposition necessitated by the original optimum SIR-balanced TPC. Moreover, the linear prediction method and adaptive on-off strategy were proposed to tackle both unbalanced SIR and global outage, respectively. Differential coding is proposed to reduce the number of bits required for the transmission of power-controlled commands.
In the sequel, the attention is turned to the derivation of the physical-layer performance for power-controlled CDMA systems. 3GPP and cdma2000, are analyzed by a unified approach. Analytical results prove that RAKE receiver and power control strategy are really necessary for improving the performance of CDMA systems. The RAKE receiver collects multipath signals to achieve a better performance. The contribution of the multipath reception is significant especially in the case of small path-strength decay factors. Even for the worst case of power control, our analyses indicate that the CDMA system with power control still outperforms that without employing power control scheme. Finally, we evaluate the capacity for spectrally overlaid power-controlled CDMA systems. The spectrally-overlaid performance over coexistent CDMA systems involving cdma2000 (wideband) and IS-95 (narrowband) is investigated. It was shown that the overlaid performance is not only dependent on the shape of transmission pulse, but on the distribution of IS-95 (narrow-band CDMA, NCDMA) subscribers over the whole available frequency band. This observation suggests that we should locate the NCDMA users over the whole frequency band carefully in order attain a better coexistence performance.

1 Introduction
2 Performance Bound of Transmitter Power Control on Multimedia CDAM Cellular Systems
3 An Alternative Derivation of the Performance Bound for Multimedia Downlink Transmitter Power Control
4 Feasible Framework for Eigen-Based Transmitter Power Control
5 Performance Analysis for Third-Generation Wideband CDMA System
6 Capacity Evaluation for Spectrally Overlaid CDMA Systems
7 Conclusions
Appendices

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