高速移動環境下WCDMA系統中通道估測與資源分配之研究

近年來無線行動通訊網路的發展已漸漸由2G到3G，甚至更新一代的系統。目前行動通訊系統可以提供語音、瀏覽網頁、收發電子郵件甚至是高傳輸速率的多媒體服務。而通訊服務所能提供的頻寬主要取決於通道的環境，當通道環境不理想時，像是使用者在移動環境時，所能取得的通訊服務頻寬就會受到限制。台灣高速鐵路已於2007年正式投入營運。目前3G行動通訊系統，以3GPP WCDMA為主流趨勢，因此如何在高速列車上提供3G的服務是一個重要的課題。通道估測在同調接收機表現上扮演一個重要的角色，高速移動使得傳統通道估測造成嚴重誤差。在本論文中針對WCDMA下鏈(downlink)方向，我們考慮接收端解展頻之前，先做通道估測。為了克服高速移動對通道估測所帶來的不良影響，我們縮短觀測時間，以個碼片(chip)為一個區塊。一個領航符號(pilot symbol)可能被分成數個由領航碼片所組成的區塊。我們採用碼片層級(chip-level)的通道估測法，每個區塊分別利用最小平方法準則估測出其通道係數。針對WCDMA上鏈(uplink)方向，我們則考慮子符號層級(sub-symbol-level)的通道估測法。縮短解展頻的週期去對抗高速移動，並加入消除路徑間干擾和雜訊的機制。此外3G無線蜂巢式網路，如WCDMA和CDMA2000被預期能支援各種多媒體應用，顯而易見的有些種類的服務交通量不再是對稱的，而是下鏈的交通量會比上鏈交通量大很多，此時下鏈無線電資源的分配變成是一個非常重要的問題，因此我們研究在一個(direct sequence- code division multiple access DS-CDMA)系統，其下鏈無線電資源管理的問題。我們把功率分配的問題，公式化成一個非線性規劃的問題。利用Frank-Wolfe Algorithm來找到全域性的最佳解；另外由於我們考慮的目標函數是可分離的，所以也可以使用lambda-method 將原非線性規劃的問題轉成一個漸進的線性規劃問題。除此之外，我們提出一個可同時考慮即時服務和非及時服務的品質導向排程問題，透過這個排程，可決定每個使用者的傳輸速率。

關鍵字

第三代行動通訊系統(WCDMA) ；通道估測；高速移動；路徑間干擾消除；功率分配；服務品質(QoS)排程

並列摘要

In the recent years, global mobile communication systems have gradually developed from 2G to 3G, and even to next generation systems. At present, mobile communication systems can provide services such as voice, web-browsing, electronic mail, and even multimedia services at a high transmission rate. The bandwidth that communication services can provide is dependent on the conditions of the channels. When the channel's conditions are not ideal, such as when the user is in a moving environment, the bandwidth of the communication service available would be limited. Taiwan's High Speed Rail officially started operations in 2007. The mainstream trend of the current 3G mobile communication systems is the 3GPP WCDMA. Thus, how to provide 3G services on a high speed vehicle is a very critical question. Channel estimation plays an important role in the performance of coherent receivers. High mobility may cause conventional symbol-level channel estimation to yield several errors. In this dissertation, we propose a chip-level channel estimation for downlink of a WCDMA system to support high mobility. In an uplink, a sub-symbol-level channel estimation is suggested to resist high mobility. Interpath interference cancellation and a moving average filter are added against interpath interference and noise. In addition, data distribution on the downlink channel is a widely-discussed issue in the research community, highlighting the importance of resource allocation to competing services on the downlink. Under given per-cell total power budget, we are able to formulate power allocation as a mathematical nonlinear optimization problem in an OVSF-CDMA system. We find that our NLP problem in an additive white Gaussian noise (AWGN)/ a Rayleigh fading/ a Rayleigh fading with diversity channel is solvable by Frank-Wolfe Algorithm or lambda-method. Moreover we incorporate the design of packet scheduler with consideration of priority, channel state and QoS requirements in deciding data transmission rates.

並列關鍵字

WCDMA ； channel estimation ； high mobility ； interpath interference cancellation ； power allocation ； QoS scheduling

參考文獻

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[2] E. Dahlman, B. Gudmundson, M. Nilsson, and J. Skold, “UMTS/IMT-2000 based wideband CDMA,” IEEE Commun. Mag., vol. 36, pp. 70–80, Sep. 1998.

[6] M.-A. R. Baissas and A. M. Sayeed, “Pilot-based estimation of time-varying multipath channels for coherent CDMA receivers,” IEEE Trans. Signal Process., vol. 50, no. 8, pp. 2037–2049, Aug. 2002.

[7] S. Bhashyam and B. Aazhang, “Multiuser channel estimation and tracking for long-code CDMA systems,” IEEE Trans. Commun., vol. 50, pp. 1081–1090, Jul. 2002.

[8] J. Evans and D. N. C. Tse, “Large system performance of linear multiuser receivers in multipath fading channels,” IEEE Trans. Inf. Theory, vol. 46, pp. 2059–2078, Sep. 2000.

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高速移動環境下WCDMA系統中通道估測與資源分配之研究

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