【正文】 應(yīng)濾波器抑制窄帶干擾等技術(shù)來提高其抗干擾能力。通過這次畢業(yè)設(shè)計，我懂得了DS擴頻系統(tǒng)其抗干擾優(yōu)越性的原理所在，并且經(jīng)過分析，自己應(yīng)用MATLAB建立起其抗各種干擾的仿真模型，并對仿真結(jié)果進行了分析從直觀的仿真曲線進一步理解了DS系統(tǒng)的抗干擾性能，而且我掌握了一定的軟件仿真能力。最后，我們可以知道由于擴頻通信本身所具有的優(yōu)越性及可提高性，使其勢必成為未來通信的主要手段。致 謝在大學(xué)四年的學(xué)習(xí)生活中，有許多人對我有很大的影響。在我將要完成我的畢業(yè)論文的時候，我在此要表達我對他們最誠摯的感謝。首先我要感謝我的指導(dǎo)老師—李白萍老師，感謝她對我畢業(yè)設(shè)計的指導(dǎo)和對我工作情況的關(guān)心。她嚴(yán)謹(jǐn)?shù)墓ぷ鲬B(tài)度，讓我受益匪淺；她在繁忙的工作之中，還要抽出時間給我們指導(dǎo)和關(guān)心我們的工作情況，讓我感動。在我即將踏入社會之際，我有幸跟著李老師，她對我將來的道路起了很大的影響，尤其是對我今后工作態(tài)度和方法起了不可替代的作用。在此我對李老師表示深深的謝意。同時，我有幸結(jié)識了我的師哥—鄭文彥。他對我來說既是老師，又是朋友。在我畢業(yè)設(shè)計期間，他對我的指導(dǎo)，讓我沒有走許多彎路，同時給我了很多重要的建議。在這方面，他是我的老師。他開朗和坦率的性格讓我們成為朋友。在這大學(xué)即將劃上句號時，我對他表示誠摯的謝意外，還要表示結(jié)識他高興的心情?；厥状髮W(xué)四年的生活，我的兄弟們給我?guī)淼目鞓泛陀颜x讓我終生難忘，在此我要提的是趙世剛、劉偉偉、何寶紅、田政等。大學(xué)四年不是一帆風(fēng)順的，我的母親和父親在我沮喪和困難時對我的支持和關(guān)愛，讓我一生難忘。我的女友—柴文麗，在我生活、學(xué)習(xí)和思想上的關(guān)懷、支持和關(guān)愛讓我銘記于心。在這此時，我將我的畢業(yè)論文奉獻給他們。現(xiàn)在我即將完成我的畢業(yè)論文，我滿懷著信心和責(zé)任踏上人生的另一端旅程，去追求人生的下一個目標(biāo)。附 錄附錄1：將一個均勻分布的隨機變量映射到瑞利分布的隨機變量的MATLAB程序：function [ray]=ray_sig(zhongzi)n=zhongzi。varR=3。u=rand(1,n)。y_exp=sqrt(2*varR*log(u))。[N_samp,r]=hist(y_exp,20)。term1=r.*r/2/varR。ray=(r/varR).*exp(term1)。附錄2：差錯率PE語音質(zhì)量＞1011101到510325103到1043104到1064＜1065表上PE單位為dB,一般通信系統(tǒng)，要求語音質(zhì)量為3或3以上,即PE＜103dB或＜。參考文獻[1] 吳明捷， [2] 吳明捷，周小正，. 石油化工高等學(xué)校學(xué)報. [3] 向春清，. [4] 查光明，： [5] 邵定蓉， [6] 富璇，. . 第1卷第1期[7] 王艷芬，張申，(MATLAB)在通信系統(tǒng)仿真中的應(yīng)用. 電訊技術(shù). . 第36卷第6期[8] 劉敏，： [9] . .[10] 曾興雯，劉乃安，孫獻璞. ： ：320,101107.[11] ，劉樹棠 —：：362372.[12] William , , , Kurt ，楊光松，許芳，席斌 ：：167168.[13] 紀(jì)國強，潘楓春，黃冬，[14] 李建新，劉乃安，：[15] 鄭阿奇，曹戈，：[16] 張葛祥，：[17] 孔文，[18] 白木，、工作方式、[19] 張瑞軍，(DS SS)[20] 梁波， 英文部分An adaptive doubledwell PN code acquisition system inDSCDMA municationsHaeSock Oh, DongSeog HanSchool of Electronic and Electrical Engineering, Kyungpook National University, 1370 SankyukDong, BukGu, Daegu 702701, KoreaReceived 27 March 2004。 received in revised form 12 January 2005Available online 12 May 2005AbstractAn adaptive doubledwell acquisition system for pseudonoise (PN) sequences is presented for directsequence spreadspectrum (DSSS) systems. Since existing acquisition systems have a fixed threshold value, they are unable to adapt to varying mobile munication environments resulting in a high false alarm rate or low detection probability. Accordingly, this study presents an adaptively varying threshold scheme that uses a constant false alarm rate (CFAR) algorithm. The performance of the proposed system is pared to the conventional doubledwell system based on deriving formulas for the detection probability, false alarm rate, and mean acquisition time of the proposed system. The results confirm that the proposed system can produce a highly improved performance over the conventional system.Keywords: Doubledwell。 Constant false alarm rate。 Adaptive detector1. IntroductionThe effective acquisition of a spreadspectrum signal is a significant aspect of mobile munication systems. In call processing, code acquisition is involved in the first stage as a foundation for further operations. Hence, the quick and accurate acquisition of a spreadspectrum signal is essential to provide highquality munication services. Typical acquisition methods include serial, parallel, and hybrid systems. Sourour and Gupta [1] introduced a new parallel acquisition system to improve the long acquisition time and low detection probability in a serial acquisition system [2]. However, since this system also requires very plex hardware, a hybrid method was suggested by Zhuang [3]. The resulting bination of serial and parallel acquisition improves the acquisition time and detection probability, plus reduces the hardware plexity of a paralleltype system. The doubledwell system was also developed [4] for fast acquisition and low false locks using simple hardware. However, all these conventional acquisition methods use a fixed threshold value, thereby resulting in varying detection probabilities and false alarm rates relative to the environment.Many researchers have proposed adaptive threshold systems for stable and quick acquisition where the threshold values are decided based on the environment. However, these systems still cannot guarantee stable acquisition because they do not include a mechanism to maintain a constant false alarm rate.Accordingly, this paper presents an adaptive threshold system for the doubledwell system. The proposed system uses a cellaveraging constant false alarm rate (CACFAR) algorithm [5] to maintain a constant false alarm rate with a low putational plexity and can acmodate a variety of mobile munication environments. The performance is analyzed and pared to existing fixed threshold systems through deriving formulas for the detection probability, false alarm rate, and mean acquisition time of the proposed system.This paper is organized as follows. Section 2 describes the acquisition scheme and Section 3 derives the expressions for the detection probability, false alarm rate, and mean acquisition time using the proposed adaptive threshold value method. The numerical results of the proposed system are presented in Section 4 along with parisons to the conventional fixed threshold doubledwell system. The findings and conclusions are then discussed in Section 5.2. System descriptionThe system under consideration in this paper is a doubledwell serial search scheme that consists of two matched filter (MF) correlators connected in a serial manner, as shown in Fig. 1, and two adaptive detectors (ADs). The shorter the correlation tap size, the higher the false alarm rate. Therefore, to pensate for this problem, the second detector is constructed with a long correlation tap size so that the acquisition system can reject those cells that are not in phase quickly. As a result, if the threshold value of the detector is controlled properly, a doubledwell system can both reduce the mean acquisition time and have a high detection probability.The system operates as follows. The transmitted pseudonoise (PN) signal, noise, and any interference arrive at each adaptive d