【正文】 瀏覽窗口。（4）模型編輯完成后保存為文件。（8）若仿真出錯，可使用建模調(diào)試工具執(zhí)行單步仿真或斷點(diǎn)調(diào)試。 本文將先用M文件的方式實(shí)現(xiàn)，再用SIMULINK的方式兩種方法實(shí)現(xiàn)。根據(jù)所使用的聲碼器種類的不同，反向業(yè)務(wù)信道支持兩種速率。移動臺在反向業(yè)務(wù)信道上以可變速率的數(shù)據(jù)發(fā)送信息，速率的選擇以幀為單位[6]。移動臺對不同速率反向業(yè)務(wù)信道的初始信息數(shù)據(jù)進(jìn)行卷積編碼。反向業(yè)務(wù)信道的符號重復(fù)率隨數(shù)據(jù)的不同而不同。為了均勻的在整個20ms幀上擴(kuò)頻數(shù)據(jù)，要使用一個數(shù)據(jù)突發(fā)隨機(jī)化算法[7]。短碼產(chǎn)生器（Short Code Generator ），產(chǎn)生I和Q短PN碼。其中，The IS95A Rev Ch Walsh Modulation and Spreading模塊（子系統(tǒng)）包含IS95A反向信道突發(fā)隨機(jī)化模塊，該模塊用于可變數(shù)據(jù)速率傳輸，起到一個選通門的作用，即基于長碼和信息幀的輸入數(shù)據(jù)速率產(chǎn)生一個的選通門信號。當(dāng)輸入信號是真實(shí)的，該模塊添加了真實(shí)的高斯噪聲，產(chǎn)生一個真實(shí)的輸出信號[10]。這個模塊使濾波器轉(zhuǎn)化為一個傳輸濾波器，濾波器被設(shè)計(jì)為在允許的頻段里最大化信號功率。這三個有效地接收端依次用短PN碼和長碼對輸入數(shù)據(jù)進(jìn)行解頻，隨后用64位Walsh碼相關(guān)聯(lián)。下面將展示三種方式，改變仿真參數(shù)。仿真時長 1 s 2 s 5 s 誤碼率 信噪比越大，表明信號越好，隨之，誤碼率越低（仿真時間5s）。信號在無線環(huán)境中傳播,經(jīng)過瑞利多徑衰弱(Rayleigh) 和加性高斯白噪聲(AWGN) 信道后,信號因衰弱和干擾而產(chǎn)生不同程度的畸變,可以清晰地看到頻譜受干擾的影響,波形圖中顯示的擴(kuò)頻信號頻譜帶有不少雜亂的干擾信號。 基于MA TLAB/ Simulink 工具箱對各功能模塊進(jìn)行建模與仿真研究，以反向業(yè)務(wù)信道為例設(shè)計(jì)出一套完整的CDMA通信仿真演示系統(tǒng),詳細(xì)分析了CDMA通信系統(tǒng)的工作方式以及信號處理過程。在我國CDMA的發(fā)展十分迅速，CDMA網(wǎng)絡(luò)架構(gòu)已經(jīng)基本初具規(guī)模。致 謝許多個日子的煎熬后，這份畢業(yè)設(shè)計(jì)終于畫上了一個句點(diǎn)。然后感謝父母、寢室舍友。參考文獻(xiàn)[1] 　樊昌信等. 通信原理(第四版) [M] .北京:國防工業(yè)出版社，2000. 162 164 ，301 303.[2] 　郭梯云,等. 移動通信[M] . 西安:西安電子科技大學(xué)出版社,2001. 293 298.[3] 　鄧華,等. MATLAB 通信仿真及應(yīng)用實(shí)例詳解[M] . 北京:人民郵電出版社,2003. 207 211 ,224 228 ,314 318.[4] 　胡鋼,等. 基于MATLAB 的遠(yuǎn)程數(shù)據(jù)傳輸系統(tǒng)的仿真研究[J ] .計(jì)算機(jī)仿真. 2001 , (5) :73 75.[5] 　徐素妍,曹坤梅. 基于MATLAB 語言的現(xiàn)代通信仿真分析[J ] .計(jì)算機(jī)應(yīng)用. 2001 , (8) :52 53.[6] 　邱剛. 基于完全互補(bǔ)碼的CDMA 通信系統(tǒng)仿真研究[D] .西安: 西南交通大學(xué), 2002.[7] 　Haykin S. Communication Systems (4t h Edition) [M] . Bei2jing : Publishing House of Elect ronics Indust ry , 2004.[8] 　Smit h P J , Shafi M , Gao H. Quick simulation : A review ofimportance sampling techniques in munication systems[J] . IEEE J Select Areas Commun , 1997 , 15 (5) : 5972613.[9] 　Sadler D , Manikas A. Blind reception of multicarrier DS2CD2MA using antenna array[J ] . IEEE Trans on Wireless Com2mun , 2003 : 2 (6) : 1 23121 239.[10] 　Sanguinetti L , Morelli M. Channel estimation for MC2CD2MA uplink t ransmission wit h bined equalization [J] .IEEE Journal on Selected Areas inCommunication , 2006 , 24(6) : 1 16721 178.[11] 　吳海鋒, 戴憲華, 梁建清. 帶有時偏的MC2CDMA 上行鏈路的盲信道估計(jì)[J ] . 通信學(xué)報(bào), 2007 , 28 (1) : 8216.[12] 　楊維, 李航. 多徑衰落信道下MC2CDMA 系統(tǒng)性能分析[J] . 電子與信息學(xué)報(bào), 2007 , 29 (6) : 1 81121 818.[13] 吳曉波 Gold碼及其偶位碼短截碼特性的計(jì)算 (2).[14] 張宏 多進(jìn)制偽碼正交調(diào)制系統(tǒng)多址性能的改善 北京郵電大學(xué)學(xué)報(bào) . 19 (4).[15] , Digital Communications. McGrawHill, New York, 1983.[16] W. W. Peterson and E. J. Weldon, ErrorCorrecting Codes (Cambridge, Mass.:MITPress, 1972).附 錄1. 英文原文An Overview of CDMACDMA BasicsCDMA systems spread a slow information bit rate with a fast chip sequence, transmit it over the air and retrieve the original information. How to actually spread and retrieve the information is standardized in details in IS95. Three main tools are used:Walsh codes, 64chip orthogonal sequencesA short code: 215 1 = 32767 chips long, which has the property of being orthogonal to any nonzero offset of itself.A long code: 242 chips long, used to generate unique sequences, which are pseudoorthogonal to oneanother.The following sections go into further details on where these tools are used in various aspects of the IS95 air interface: on forward links, reverse links, in access mode, and in traffic mode.Walsh CodesForward Link Walsh codes are orthogonal codes, IS95 uses them to multiplex several mobile munications (and control channels) on the forward link. In the forward link, each mobile uses a specific Walsh code sequence。 this noise represents the interference generated by other base stations that are using the same frequency band.In the receiver section, the ining signal is first filtered by the Receive Filter block, which implements a filter matched to the transmit filter. The filters in this demo are designed to maximize the signal power within the desired frequency band.Then the filtered signal is sent to the IS95A Rev Ch Detector library block, which contains the reverse channel rake receiver. The rake receiver consists of three rake fingers that are set to different delays to handle up to three multipaths. Each active rake finger performs the despreading of the input data with the short PN sequence, followed by despreading with the long code. This is followed by the correlation with the entire set of 64 Walsh codes. The energies in the I and Q ponents are added, and the results from the fingers are added together. This is processed by the Walsh demodulator, which generates decisions in groups of 6 bits, the size used for modulation. The Walsh demodulator outputs both soft decisions and bipolarvalued hard decisions. both are gated by the data burst randomizer signal.The Error Rate Calculation block pares the transmitted bits and the received decisions, and produces the raw (that is, without channel coding) bit error rate. This rate is displayed in the model window during the simulation.Visible Results of the DemoThe demo shows the raw bit error rate (BER) for the reverse channel. The BER depends on the channel conditions and the number of rake receiver fingers active. As the signaltonoise ratio or the channel conditions are changed, the effect of these on the raw BER can be seen by running the model for these different conditions.Changing Demo ParametersThis section suggests some ways that you can alter the parameters in the demo after you understand the model.The simulation duration in this demo is set to 2 seconds. Because the frame duration in IS95A is second, this model processes 100 frames. This gives a sufficient time for the BER measurements to converge at reasonable SNR settings. To run the simulation for a longer or shorter time, select Parameters from the Simulation menu and change the Stop time to times the number of frames you want to simulate.To change the data rate, doubleclick on the Data Source icon. Then doubleclick on the Mobile Station Transmitter Data Rate icon a