【正文】 00Hz, 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。s main performance indicators 1) The processing gain is the tolerance and antijamming spreadspectrum munication systems are two important performance , also known as processing gain spread spectrum gain (Spreading Gain) it is defined as the information before spread spectrum 6 bandwidth expansion band DF and the signal bandwidth W ratio: FWGP ?? / （ 5） In spread spectrum munication system. Demodulation for spreadspectrum receiver, the only pseudorandom code extract treatment, the bandwidth related to the information DF, and ruled out the external Wwideband interference, noise and its impact to the user39。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。 At the same time, different users use different code, others can not be tapping their munications, thus spreadspectrum system with high confidentiality. 4 Spread Spectrum Communication in the MATLAB simulation Direct Sequence Spread Spectrum system BER simulation According to Shannon theorem, we can see: ）（ NSWLC /1og ?? （ 7） Where: W for the transmission bandwidth。 F For the signal frequency。 0N For the noise power spectral transmission bandwidth W ,Signal power TES /? ,Noise Power 0WNN? ,Signal duration T ,Information signal bandwidth TF /1?? ,Into the type(8) ,a： FWNSNST WNE ???0 (9) Style (9) Description, eP By FWNS? Decision,In other words, a certain bandwidth transmission F? Information,SNR NS And bandwidth can beW Exchange. Binary sequences for spread spectrum munication of information, assuming that the information rate of R , Symbol interval is SRT /1b? ,Effective bandwidth to transmit information to )m( RBB CC .In the DS system, the use of MatLab toolbox function of the pseudorandom sequence to generate pseudorandom code sequence. There is the PN code is a 9 bit more than 0,1 code sequences, which undergo a rigorous selection process, and has a good autocorrelation, but similar to each other but are mutually orthogonal, linearly independent and, in many key type, they can easily identify with their own code the same type, and not easily confused with other codebased. The use of PN sequences in the transmitter, the message sequence will be the expansion of narrowband wideband signal for transmission into the channel, the receiver will receive the broadband signal synchronized with the transmitter PN sequence multiplied, the narrowband despread the message sequence, and the types of interference signals are multiplied with the PN sequence to the expansion of the form for broadband,Will eventually weaken the energy of interference signal W / R times. In the modulator, the message sequence for the bandwidth expansion CBW? ,Prevalent as a result of transmission interference, and therefore must be taken into account in the simulation of the interference signal of the decision ruling the impact of device. Assuming that the process of signal transmission by the cosine form of interference with the role of signal, the signal current of )2co s()( tfAti jj ?? (10) Type (10): jf In order to send the signal interference within the frequency bandwidth. )(ti and )(tc Multiplied so that cosine form of interference into the broadband interference，Its energy density spectrum WPJ J /0 ? ,Where: 2/2JJ AP ? For the average energy of interference order to more intuitive analysis of DSsinusoidal interference signal suppression ef