【正文】 設(shè)計室外地坪至檐口高度 00m，呈長方形布置，東西向，三個單元。 一、 工程概況： 西夏建材城生活區(qū) 2 30住宅樓位于銀川市新市區(qū) ，橡膠廠對面。 0N 為噪聲功率譜密度 .將傳輸帶寬 W ,信號功率 TES /? ,噪聲功率 0WNN? ,信號持續(xù)時間 T ,信息信號帶寬TF /1?? ,代入式 (8) ,得 FWNSNST WNE ???0 (9) 式 (9) 說明 , eP 是由 FWNS? 決定的 ,就是說 ,傳輸一定帶寬 F? 的信息 ,信噪比 NS 可以和帶寬 W 互換 . 對于二進(jìn)制信息序列的擴(kuò)頻通信 ,假設(shè)信息速率為 R , 碼元間隔為 SRT /1b? , 傳輸信息的有效帶寬為 )m( RBB CC .在直擴(kuò)系統(tǒng)中 ,采用 MatLab 工具箱中的偽隨機序列函數(shù)來生成偽隨機碼序列 . 此中的 PN碼是具有多個碼位的 0,1 序列 ,它們是經(jīng)過嚴(yán)格挑選的 ,具有良好的自相關(guān)性 ,但彼此之間 卻近似是相互正交 ,與線性無關(guān) ,在眾多碼型中 ,它們很容易識別出與自己相同的碼型 ,而不容易與其它碼型混淆 . 利用在發(fā)射機中 PN 序列 ,將窄帶的信息序列擴(kuò)展為寬帶信號送入信道傳輸 ,在接收端將接收的寬帶信號與發(fā)送端同步的PN 序列相乘 ,解擴(kuò)出窄帶的信息序列 ,而各種干擾信號被與 PN 序列的相乘處理擴(kuò)展為寬帶形式 ,最終將干擾信號的能量削弱 W/R 倍 .在調(diào)制器中 ,信息序列的帶寬擴(kuò)展為 CBW? ,由于傳輸中普遍存在干擾 ,因此在仿真時必須考慮到干擾信號對判決器判決結(jié)果的影響 . 18 假設(shè)在信 號傳輸過程中受到干擾信號為余弦形式作用 ,則該信號電流為 )2co s()( tfAti jj ?? (10) 式 (10)中 : jf 為發(fā)送信號帶寬內(nèi)的干擾頻率 . )(ti 與 )(tc 相乘使余弦形式的干擾變?yōu)閷拵Ц蓴_ ,其能量譜密度為 WPJ J /0 ? ,式中 : 2/2JJ AP ? 為干擾信號的平均能量 .為了更直觀地分析直擴(kuò)信號抑制正弦干擾的效果 ,建立了 Monte Carlo 仿真模型 , 圖 2 直擴(kuò)系統(tǒng) Monte Carlo 仿真模型 由圖 2可以看出 ,由隨機數(shù)發(fā)生器產(chǎn)生一系列二進(jìn)制 (177。由于在擴(kuò)頻通信系統(tǒng)中增加了擴(kuò)頻調(diào)制與解擴(kuò)過程 ,這樣可以利用擴(kuò)頻碼序列間的相關(guān)特性 ,在接收端解擴(kuò)時用相關(guān)技術(shù)從多徑信號中分離出最強的有用信號 ,或?qū)⒍鄰叫盘栔械南嗤a序列信號疊加 ,這樣就可以有效地消除無線通信中多徑干涉造成的信號衰落現(xiàn)象 ,因而擴(kuò)頻通信系統(tǒng)具有良好的抗多徑衰落 17 特性。由于擴(kuò)頻信號的上述特點 ,擴(kuò)頻系統(tǒng)具有以下特點 : 抗干擾性強 由于擴(kuò)頻信號的不可預(yù)測性 ,擴(kuò)頻系統(tǒng)具有很高的抗干 擾能力。 處理增益 G 也稱擴(kuò)頻增益 (Spreading Gain) 它定義為頻譜擴(kuò)展前的信息帶寬 DF 與頻帶擴(kuò)展后的信號帶寬W之比： FWGP ?? / （ 5） 在擴(kuò)頻通信系統(tǒng)中．接收機作擴(kuò)頻解調(diào)后，只提取偽隨機編碼相關(guān)處理后的帶寬為DF 的信息，而排除掉寬頻帶 W 中的外部干擾、噪音和其地用戶的通信影響。信息論中關(guān)于信息容量的香農(nóng) (Shannon)公式為： ）（ NPWLC /1og 2 ?? (2) （ 2） 式中： C 信道容量 (用傳輸速率度量 ) W 信號頻帶寬度 P 信號功率 N 白噪聲功率 式 (2)說明，在給定的傳輸速率 C 不變的條件下，頻帶寬度 W 和信噪比 NP/ 是可以互換的。弄清楚擴(kuò)頻和解擴(kuò)處理過程的機制，是 理解擴(kuò)頻通信本質(zhì)的關(guān)鍵所在。這里需要說明的一點是所采用的擴(kuò)頻碼序列與所傳信息數(shù)據(jù)是 無關(guān)的，也就是說它與一般的正弦載波信號一樣，絲毫不影響信息傳輸?shù)耐该餍浴槭裁匆眠@樣寬的頻帶的信號來傳輸信息呢 ? 這樣豈不太浪費寶貴的頻率資源了嗎 ? 2）采用擴(kuò)頻碼序列調(diào)制的方式來展寬信號頻譜。 我們知道，傳輸任何信息都需要一定的帶 寬，稱為信息帶寬。 衡量擴(kuò)頻系統(tǒng)最重要的一個指標(biāo)就是擴(kuò)頻增益，又稱為處理增益。s decision to record the number of wrongful convictions . Analysis of simulation results Adding noise and interference, the access CL = 10 ,With three different sinusoidal signal interference, the amplitude of 2, 3, 7. In bit error rate in puting the variance of additive noise is fixed, a total of 10,000 calculations, and each operator, the signal energy values are required to meet the requirements of the signal to noise ratio, which has been shown in Figure 3 the simulation be seen that the amplitude of the sinusoidal interference signal the greater the greater the error rate. Similarly, in the same signal to noise ratio, the greater the processing gain, the smaller the error rate, and in large signal to noise ratio, this difference is particularly evident. Figure 3 MonteCarlo simulation of the spread spectrum munication system the interference of different amplitude sine BER simulation curves 11 5 Conclusion 1)The author in this paper, the establishment and optimization of the Monte Carlo simulation model, can be a variety of direct sequence spread spectrum munication system bit error rate simulation analysis, simulation results show that the DS is capable of ruling system to the smaller errors the probability of the restoration of the original signal, the verdict has the excellent performance. 2) in the same signal to noise ratio, the greater the processing gain, the smaller the error rate, especially in the large signal to noise ratio, this difference is particularly evident。s ability to work, is defined as: ]s)/[( outj LNSGM ??? （ 6） Of which: jM Antiinterference capacity G Processing gain out)/( NS Information data is correct and the requirements of the smallest demodulator output signal to noise ratio sL The work of the receiving system loss Spread Spectrum Communication System working principle Digital Spread Spectrum Communication general working principle as shown in Figure 1. Figure 1 the number of the basic block diagram of spread spectrum munication system Shown in Figure 1 for a digital spread spectrum munication system, the basic block channel encoder, channel decoder, modulator and demodulator is a traditional digital munication systems constitute the basic spectrum munication system in the removal of these units, should use the same pseudorandom sequence generator, sending the frontend, respectively, the role of the modulator and demodulator to receive the front two pseudorandom sequence generator noise (PN) binary sequence, the client 7 will send the signal modulation in the frequency domain for the expansion, in the end demodulation despreading the spread spectrum signal. 3 Characteristics of Spread Spectrum Communication System Spread spectrum signal is unpredictable pseudorandom broadband signal bandwidth is much larger than its wish to transfer data (information) bandwidth, at the same time, the receiver must be synchronized with a copy of broadband carrier .Spreadspectrum signal as a result of these characteristics, spread spectrum system has the following characteristics: The strong antijamming Due to the unpredictability of spreadspectrum signal, the spread spectrum system has a high antiinterference difficult because of interference by observing interference to improve their performance, and can only be fired with the interference of the interference signal does not match the technology, therefore, would not contribute significantly interfere。Frequencyhopping system using pseudorandom code to control the carrier frequency in a wider band of the change。TH is the data transmission time slot is a pseudorandom。 As the spread spectrum munication system in the transmission signal bandwidth expansion, so even if the signal to noise ratio is very low, even lower than the useful signal power of interference signal power is still the case t