【正文】 ications receiver and transmitter used the same spread spectrum code sequence spread spectrum signals received by the relevant demodulation, the restoration of the mass of other words, this correlation despreading demodulation role to is, to expand beyond the original signal is restored by the mass of information. This narrowband information in the originator to expand into the broadband signal, and in 4 the closeend solution will expand its narrowband information into the process, will bring a number of extended to clarify the process of reconciliation mechanism is to understand the nature of spread spectrum munication key. The theoretical basis for spread spectrum munication A long period of time, people have the idea of the signal as far as possible the occupation of the narrow spectrum in order to take full advantage of very valuable spectrum use such a broadband signal to transmit information? The short answer is mainly to secure munication .The basic characteristics of spread spectrum munication is the transmission signal bandwidth occupied by (W) is much larger than the original information to their actual minimum requirements (effective) bandwidth (DF), the ratio referred to as processing gain Gp: FWGP ?? / (1) As we all know, any information needed for effective transmission of the frequency of a certain width, such as the voice for the , television images were a few MHz order to make full use of limited frequency resources, increasing the number of channels, it is a wide selection of different modulation methods, the use of broadband channel (coaxial cable, microwave and fiberoptic, etc.), and measures such as pression band, at the same time strive to make the transmission of the signal transmission media occupy a narrow bandwidth as much as possible. Due to the current use of the telephone, radio system, whether it is using AM, FM, or pulse code modulation format, Gp values are within the scope of more than 10 times, collectively referred to as narrowband munications.Gp of the spread spectrum munication value, up to hundreds, thousands, known as broadband munications.The feasibility of spread spectrum munication, information theory and antijamming from the basic formula of the theory of extension on the Shannon information capacity (Shannon) formula is: ）（ NPWLC /1og 2 ?? (2) （ 2） Where: C Channel capacity (with transmission rate measurement) W Signal bandwidth P Signal power N White noise power 5 Type (2) shows that： In a given transmission rate C under the same conditions, the bandwidth W and the signaltonoise level NP/ are increasing the bandwidth to the method, at a relatively low signal to noise ratio NP/ ( NS/ ), the transmission of spectrum signal to noise ratio requirements for the reduction is an important feature of spread spectrum munication, and thus the application of spread spectrum munication for the foundation. Spread spectrum munication based on the feasibility of another theory for the transmission of information Baryshnikov error probability formula: ）（ 0j /fow NEP ? （ 3） Where: jPow Error Probability E Signal energy 0N Noise power spectral density Signal power TEP /? (T for the duration of information) Noise Power 0WNN? (W for the signal band width) Information bandwidth TDF /1? The type (3) can be translated into: )//(/ow FWNPfNPTWfP ????? ）（ （ 4） (4) shows that for a certain bandwidth of the information in terms of DF , with PG values greater broadband signal transmission, antiinterference ability can improve munications to ensure that under conditions of strong interference, safe and reliable is, (4) and type (2) the same signal to noise ratio and bandwidth that can be interchangeable. In short, we use the information bandwidth of 100 times, or even 1000 times higher than the broadband signal to transmit the message that in order to improve the munication of antiinterference ability, that is in strong interference conditions to ensure safe and reliable is the spreadspectrum munications based on the basic ideas and theories. Spread Spectrum Communication39。 華科學院 HUAKE INSTITUTE OF TAIYUAN UNIVERSITY OF SCIENCE amp。Receiving end in the same synchronization code related to receiving, despreading and recovery of the mass data. This definition includes the meaning of the following three aspects: 1)The signal spectrum by a broadening. We know that the transmission of any information needs to a certain bandwidth, as the information example, the human voice information bandwidth of 300Hz 3 3400Hz, television image information bandwidth of order to make full use of frequency resources, which are roughly the same as far as possible the signal bandwidth to transmit the radio munication bandwidth RF signals with the mass of information is parable to the as the AM signal used to transmit voice messages, voice messages of their bandwidth for twice the bandwidth。 F For the signal frequency。擴頻通信是將待傳送的信息數(shù)據(jù)被偽隨機編碼 (擴頻序列： Spread Sequence)調(diào)制，實現(xiàn)頻譜擴展后再傳輸；接收端則采用相同的編碼進行解調(diào)及相關(guān)處理，恢復原始信息數(shù)據(jù)。近年來，隨著超大規(guī)模集成電路技術(shù)、微處理器技術(shù)的飛速發(fā)展，以及一些新型元器件的應用，擴頻通信在技術(shù)上已邁上了一個新的臺階，不僅在軍事通信中占有重要地位，而且正迅速地滲透到了個人通信和計算機通信等民用領域，成為新世紀最有潛力的通信技術(shù)之一。如用調(diào)幅信號來傳送語音信息，其帶寬為語音信息帶寬的兩倍；電視廣播射頻信號帶寬也只是其視頻信號帶寬的一倍多。 1微秒的脈沖的帶寬約為 1MHz。在擴頻通信中接收端則用與發(fā)送端相同的擴頻碼序列與收到的擴頻信號進行相關(guān)解調(diào)，恢復所傳的信息。為了充分利用有限的頻率資源，增加通路數(shù)目，人們廣泛選擇不同調(diào)制方式，采用寬頻信道 (同軸電纜、微波和光纖等 )，和壓縮頻帶等措施，同時力求使傳輸?shù)拿浇橹袀鬏數(shù)男盘栒加帽M量窄的帶寬。亦即式 (4)與式 (2)一樣，說明信噪比和帶寬是可以互換的 。其中信道編碼器、信道解碼器、調(diào)制器和解調(diào)器是傳 統(tǒng)數(shù)字通信系統(tǒng)的基本構(gòu)成單元。因此 ,擴頻通信系統(tǒng)具有低截獲概率性。 4 擴頻通信在 MATLAB 仿真中的應用 直接序列擴頻系統(tǒng)誤碼率的仿真 根據(jù)香農(nóng)定理可知 : ）（ NSWLC /1og ?? （ 7） 式中 :W 為傳輸帶寬 。而在處理增益不變時 ,正弦干擾信號振幅增加 ,誤碼率則增大。30樓 m2