【導讀】穩(wěn)定性，在比較三種常用網(wǎng)絡仿真模型的基礎(chǔ)上，分析了時隙ALOHA仿真結(jié)果及應用于通信系統(tǒng)中的性能優(yōu)點。給出了MATLAB仿真平臺下實現(xiàn)時隙ALOHA控制算法的流程圖，編寫了MATLAB代碼對時隙AL0HA的偽貝葉控制算。法性能進行協(xié)議性能測試及仿真結(jié)果表示。2多地址接入?yún)f(xié)議發(fā)展狀況·························································································4. 多地址接入?yún)f(xié)議概述·······················································································5. 多址接入?yún)f(xié)議分類·······&#

　　

【正文】 于無捕獲效應下的數(shù)據(jù)包延遲個數(shù)。我們的仿真結(jié) 果也證實是這一點。 通過對以上兩個仿真結(jié)果圖的分析中，我們可以發(fā)現(xiàn)其實上述兩圖要表達的意思其實是一樣的吞吐量是傳送成功的數(shù)據(jù)包的個數(shù)。延遲數(shù)據(jù)包的個數(shù)是由于碰撞而沒有發(fā)送成功的數(shù)據(jù)包。在有捕獲效應的情況下，吞吐量升高，那數(shù)據(jù)包延遲個數(shù)就會下降，反之一樣。 陜西理工學院畢業(yè)設(shè)計 第 19 頁 共 39 頁 結(jié)論 現(xiàn)代通信網(wǎng)絡的復雜和頻譜資源的緊缺，使如何分配信道的接入權(quán)成為一個非常關(guān)鍵的問題。無論是在局域網(wǎng)中、還是無線通信網(wǎng)絡中，接入技術(shù)在解決數(shù)據(jù)沖突和提高網(wǎng)絡吞吐量等方面都表現(xiàn)出了出色的功能，在實際應 用中，由于業(yè)務的突發(fā)性與實時性，還存在一定的問題。因此隨著網(wǎng)絡業(yè)務的復雜與增多，研究信道接入技術(shù)，根據(jù)網(wǎng)絡業(yè)務特征有效地分配信道資源，提高資源的利用率，改善網(wǎng)絡性能，仍然是通信網(wǎng)絡研究的重要內(nèi)容。本文首先介紹了隨機多址接入?yún)f(xié)議的研究背景及主要成果，從常用的網(wǎng)絡參考模型入手，對目前廣泛研究的純 ALOHA 協(xié)議、時隙 ALOHA 協(xié)議、非持續(xù)性 CSMA 協(xié)議進行了詳細闡述，具體分析了這三種協(xié)議的基本原理、系統(tǒng)吞吐量、平均傳輸時延等性能指標，然后基于 Matlab 平臺進行建模仿真，對所得數(shù)據(jù)進行了分析，進而比較得出 不同類型的多址系統(tǒng)的優(yōu)缺點，為提高協(xié)議性能提供了參考。 ALOHA 和 CSMA 協(xié)議作為基礎(chǔ)的隨機多址接入?yún)f(xié)議，目前仍廣泛應用。其中 ALOHA 協(xié)議適合應用于用戶負載較低的場合，隨著用戶數(shù)量或發(fā)送信息量的增加，這種完全隨機接入的協(xié)議將使沖突概率增大，傳輸性能降低。 CSMA 協(xié)議在性能上雖然優(yōu)于 ALOHA，但是在服務質(zhì)量保證（尤其是實時業(yè)務支持）方面仍然難以滿足要求，基于 CSMA 的協(xié)議主要應用于短距離數(shù)據(jù)業(yè)務的多址接入，比如計算機局域網(wǎng)的互聯(lián)接入等。隨著音頻、視頻等多媒體業(yè)務的普及，以及工業(yè)應用方面等的特殊要 求，使得傳統(tǒng)的 ALOHA 和 CSMA 協(xié)議逐漸顯得有些捉襟見肘，尤其是在無線局域網(wǎng)方面的 CSMA/CA 系統(tǒng)，目前人們對無線網(wǎng)絡的呼聲也越來越高，當然對網(wǎng)絡質(zhì)量的要求也是越來越苛刻。為適應多媒體業(yè)務接入需要，接下來仍需要對多址接入?yún)f(xié)議進行深入的研究。 陜西理工學院畢業(yè)設(shè)計 第 20 頁 共 39 頁 致謝： 本課題的研究是在 吳燕 老師的精心指導下完成的，感謝她在我學習期間給我的關(guān)心、鼓勵和幫助。從論文的選題到最后的定稿， 吳 老師都給予了我悉心的指導，并給了我一個學習與提高的機會，使我的畢業(yè)論文能順利的完成。 吳 老師嚴謹?shù)闹螌W態(tài)度、淵 博的學識、刻苦專研的科研精神和兢兢業(yè)業(yè)的工作態(tài)度都給我留下了深刻的印象，將對我以后的學習和工作產(chǎn)生深遠的影響。在此，本人對導師表示深深的敬意和最誠摯的感謝。感謝 陜西理工學院 為我提供了優(yōu)良的學習條件，優(yōu)雅的學習環(huán)境， 陜西理工學院 濃厚的學術(shù)氛圍將使我終身難忘。在大學四年中，我學到了很多知識，開闊了視野，感到受益匪淺。感謝 物理與電信工程 學院及里 通信學院 的老師們的指導和幫助！最后，感謝我的父母和家人，他們殷切的期望是我不斷進取的動力，他們在各方面都給予了我最無私的幫助和支持，同時，也感謝所有關(guān)心和幫助過我的同學和朋 友們！ 陜西理工學院畢業(yè)設(shè)計 第 21 頁 共 39 頁 參考文獻 [1] of Metropolitan Area . [2]徐洋 ,朱近康 .無線通信中的隨機接入?yún)f(xié)議研究 .通信技術(shù) .安徽 :合肥出版社 ,. [3]范謙 ,李式巨 .無線局域網(wǎng) MAC 接入性能分析 .無線電工程 .. [4]劉學勇 .詳解 MATLAB/Simulink 通信系統(tǒng)建模與仿真 .北京 :電子工業(yè) 出版社 ,. [5]王申濤 ,楊浩 ,周熙 .幾種隨機接入?yún)f(xié)議的仿真性能比較分析 .計算機與現(xiàn)代化 .. [6]聶景楠 .多址通信及其接入控制技術(shù) .北京 :人民郵電出版社 ,. [7]佘明輝 ,趙東風 .基于隨機多址協(xié)議的系統(tǒng)吞吐量分析 .吉林大學學報 ,. [8]王秉鈞 .ALOHA 協(xié)議的性能分析 .天津通信技術(shù) .. [9]錢華林 .Nonpersistent CSMA 協(xié)議的容量 .計算機學報 ,. [10]張婷 .基于 OPNET 的多址接入控制技術(shù)研究 .重慶 :重慶大學碩士學位論文 ,. 陜西理工學院畢業(yè)設(shè)計 第 22 頁 共 39 頁 RESEARCH OF CELLULAR WIRELESS COMMUNATION SYSTEM Abstract Cellular munication systems allow a large number of mobile users to seamlessly and simultaneously municate to wireless modems at fixed base stations using a limited amount of radio frequency (RF) spectrum. The RF transmissions received at the base stations from each mobile are translated to bandsmen, or to a waveband microwave link, and relayed to mobile switching centers (MSC), which connect the mobile transmissions with the Public Switched Telephone Network (PSTN). Similarly, munications from the PSTN are sent to the base station, where they are transmitted to the mobile. Cellular systems employ either frequency division multiple access (FDMA), time division multiple access (TDMA), code division multiple access (CDMA), or spatial division multiple access (SDMA). 1 Introduction A wide variety of wireless munication systems have been developed to provide access to the munications infrastructure for mobile or fixed users in a myriad of operating environments. Most of today’s wireless systems are based on the cellular radio concept. Cellular munication systems allow a large number of mobile users to seamlessly and simultaneously municate to wireless modems at fixed base stations using a limited amount of radio frequency (RF) spectrum. The RF transmissions received at the base stations from each mobile are translated to bandsmen, or to a waveband microwave link, and relayed to mobile switching centers (MSC), which connect the mobile transmissions with the 陜西理工學院畢業(yè)設(shè)計 第 23 頁 共 39 頁 Public Switched Telephone Network (PSTN). Similarly, munications from the PSTN are sent to the base station, where they are transmitted to the mobile. Cellular systems employ either frequency division multiple access (FDMA), time division multiple access (TDMA), code division multiple access (CDMA), or spatial division multiple access (SDMA) . Wireless munication links experience hostile physical channel characteristics, such as timevarying multiparty and shadowing due to large objects in the propagation path. In addition, the performance of wireless cellular systems tends to be limited by interference from other users, and for that reason, it is important to have accurate techniques for modeling interference. These plex channel conditions are difficult to describe with a simple analytic model, although several models do provide analytic tractability with reasonable agreement to measured channel data . However, even when the channel is modeled in an analytically elegant manner, in the vast majority of situations it is still difficult or impossible to construct analytic solutions for link performance when error control coding, equalization, diversity, and work models are factored into the link model. Simulation approaches, therefore, are usually required when analyzing the performance of cellular munication links. Like wireless links, the system performance of a cellular radio system is most effectively modeled using simulation, due to the difficulty in modeling a large number of random events over time and space. These random events, such as the location of users, the number of simultaneous users in the system, the propagation conditions, interference and power level settings of each user, and the traffic demands of each user,bine together to impact the overall performance seen by a typical user in the cellular system. The aforementioned variables are just a small sampling of the many key physical mechanisms that dictate the instantaneous performance of a particular user at any time within the system. The term cellular radio system,therefore, refers to the entire population of mobile users and base stations throughout the geographic service area, as opposed to a single link that connects a single mobile user to a single base station. To design for a particular systemlevel performance, such as the likelihood of a particular user having acceptable service throughout the system, it is necessary to consider the plexity of multiple users that are simultaneously using the system throughout the coverage area. Thus, simulation is needed to consider the muftiuser effects upon any of the individual links between the mobile and the base station. The link performance is a smallscale phenomenon, which deals with the instantaneous changes in the channel over a small local area, or small time duration, over which the average received power is 陜西理工學院畢業(yè)設(shè)計 第 24 頁 共 39 頁 assumed constant . Such assumptions are sensible in the design of error control codes, equalizers, and other ponents that serve to mitigate the transient effects created by the channel. However, in order to determine the overall system performance of a large number of users spread over a wide geographic area, it is necessary to incorporate largescale effects such as the statistical behavior of interference and signal levels experienced by individual users over large distances, while ignoring the transient channel characteristics. One may think of linklevel simulation as being a vernier adjustment o