衰減通道下延遲鎖相迴路之效能分析

Performance of the Digital Delay-Lock Loop over the fading channels

莊宗華(Chung-Hua Chuang)

指導教授 ： 吳燦明

中原大學/工學院/電機工程研究所/碩士(2004年)

https://doi.org/10.6840/cycu200400772

摘要

直接序列分碼多工技術，也就是所謂的展頻多工系統，最近幾年已經非常普遍的應用在陸地上與衛星上的通訊系統。此通訊技術擁有較有效率的頻寬使用性、較好的通訊品質、抗干擾等優點，使得非常多的新一代的通訊系統都採用此技術，例如：cdma2000, UMTS-UTRA (Universal Mobile Telecommunications System - Universal Terrestrial Radio Access) network, wideband CDMA (DoCoMo), TD-CDMA (time division duplex CDMA), and TD-SCDMA (time division synchronous CDMA)。然而，傳送端與接收端的擬亂碼(Pseudorandom code)同步對於展頻技術而言是非常重要的。此擬亂碼的同步可分為兩個部份，一個是擬亂碼的擷取(acquisition)，另一個是擬亂碼的追蹤(tracking)。在我們的研究裡，我們將假設擬亂碼的擷取已經做好，進而去分析擬亂碼的追蹤。
對於擬亂碼的追蹤而言，延遲鎖相迴路(delay-lock loop)是一種很常用的技術。在白色高斯雜訊的環境下，已經有很多學者去探討此迴路的效能。延遲鎖相迴路受督卜勒效應與多重存取干擾的影響下的效能，亦被其他學者所研究過。對於無線傳輸環境，衰減通道是一個非常重要的參考因素。當然，類比的延遲鎖相迴路在此環境下也被探索過。但是對於數位的延遲鎖相迴路而言，在Nakagami-m, Ricean, Hoyt, Weibull 等四種衰減通道下，其效能尚未被分析。因此，我們將在此分析延遲鎖相迴路在此四種衰減通道下的效能。其效能分析包括：求得穩態時間差的機率密度函數與平均失鎖時間(Mean Time to Lose Lock)。第一章將簡單的介紹此論文。擬亂碼的性質將在第二章裡作解說。第三章將會對傳統的類比鎖相迴路做簡單的分析。數位延遲鎖相迴路於四種衰減通道的效能將在第四張裡作完整描述。第五章則會對此論文做一個總結。

關鍵字

衰減通道 ； 延遲鎖相迴路 ； 直接序列展頻系統 ； 同步

並列摘要

Direct-sequence code-division multiple-access (DS-CDMA) technologies, also known as spread-spectrum multiple-access schemes, have become very popular for various terrestrial and satellite application recently. It has been experienced that spread-spectrum systems can provide larger capacity, more efficient utilization of the spectrum, better speech quality through using low-bit-rate linear predictive coders, more robust communication of data services in employing efficient channel coding, and greater bandwidth per channel, thereby, leading to the possibility of genuine multimedia services in wireless networks. Due to these advantages, many new generation communication systems, such as cdma2000, UMTS-UTRA (Universal Mobile Telecommunications System - Universal Terrestrial Radio Access) network, wideband CDMA (DoCoMo), TD-CDMA (time division duplex CDMA), and TD-SCDMA (time division synchronous CDMA), attempt to use the spread-spectrum technigues. However, it is necessary for DS-SS systems that the pseudonoise (PN) code of the receiver is synchronized with that of the transmitter. There are two portions for the system synchronization. One is the determination of the initial code phase, also named the code acquisition. The other part lies in the maintenance the synchronization after the initial acquisition, called the code tracking. Here, we will only cope with the second part under the fading environments by assuming that the initial acquisition has been done.
The PN code tracking with a delay-lock loop (DLL) is commonly used for the code synchronization in DS-SS communication systems. Substantial efforts have been focused on the tracking problem, even though most of the analyses have been conducted in the context of additive white Gaussian noise channels. The effects of Doppler shifts and multiple-access interference have been also investigated. Additionally, in the mobile radio environments, the influence of the fading phenomenon, on the tracking performance of the DLL has been also studied. However, the performance of digital non-coherent delay-lock loop (DDLL) for spread-spectrum signals has not been analyzed yet over Nakagami-m, Ricean, Hoyt, and Weibull fading channels. These fading channels play an important role in the mobile radio environment. We first evaluate the tracking performance of the DDLL over the four fading channels, including the steady-state timing error PDF and the MTLL with their numerical results being confirmed via computer simulations. This thesis is organized as follows. Chapter 1 gives the introduction to this thesis. Chapter 2 presents the properties of the PN sequence. The analysis of the conventional analog DLL are treated in Chapter 3. The performance of the non-coherent DDLL over the four fading channels is provided in Chapter 4. The MTLL analysis for the DDLL is carried out in section. Chapter 5 concludes the paper with remarks and suggests future research.

並列關鍵字

fading channel ； delay-lock loop ； direct-sequence spread-spectrum system ； synchronization

參考文獻

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