1、 Spread Spectrum Communication System and MATLAB Simulation ABSTRACT This thesis expounds the basic principles of spread spectrum communication , and then the article mainly acts according to the Shannon theorem and tan oak Czechoslovakia you Nepal may the husband latent antijamming theory,With the
2、aid of MatLab toolbox and Monte Carlo simulation algorithm,it has established the direct sequence spread spectrum communications system simulation model which does not have when the disturbance through the analysis error rate simulation curve and theory predicted value,had proven constructs the simu
3、lation model the accuracy. Key words： Spread spectrum； communication； MATLAB 1 Introduction 1.1 Spread Spectrum Communication System Spread spectrum communication, namely, spread spectrum communications (Spread Spectrum Communication), with fiber-optic communications, satellite communications, with
4、access to the information age as the three major high-tech communications transmission.Spread spectrum communication is to send the information to be pseudo-random data is coded (spread spectrum sequence: Spread Sequence) modulation, spread spectrum and then the realization of transmission； the rece
5、iving end is using the same modem code and related processing, the restoration of the original data.Spread spectrum communication system has three main characteristics. Carrier is an unpredictable, or so-called pseudo-random broadband signal. Carrier data bandwidth than the modulation bandwidth is m
6、uch wider. Receiving process is generated by local broadband carrier signal and receiving a copy of the signal to the broadband signal to achieve. The main way of spread spectrum are as follows:Direct Sequence Spread Spectrum (DSSS) using high-speed pseudo-random code on to the low-speed data transm
7、ission spread spectrum modulation；Frequency-hopping system using pseudo-random code to control the carrier frequency in a wider band of the change；TH is the data transmission time slot is a pseudo-random；Chirp frequency system is a linear extension of the process of change.Combination of a number of
8、 ways of hybrid systems are often applied. - 2 - The most important measure of spread-spectrum system is an indicator of spreading gain, also known as processing gain.It is precisely because of the spread spectrum system itself with its performance characteristics with a series of advantages. 1.2 Th
9、e purpose of spread spectrum communication studies and significance Spread spectrum communication is an important branch of communication and channel the direction of development of communication systems.Spread-spectrum technology, with strong anti-interference ability, confidentiality, and is easy
10、to realize the advantages of multiple-access communications, so the technology is receiving increasing attention.In recent years, with very large scale integrated circuit technology, the rapid development of microprocessor technology, as well as the application of some new components, spread spectru
11、m communications is technically feasible to enter a new level, not only in an important military communications status, and are quickly penetrated into the personal communications and computer communications and other civilian areas, to become the new century, the most potential of communication tec
12、hnologies.The study is spread spectrum communication with far-reaching significance, I through the thesis the design, conduct in-depth study of the spread spectrum communication technology and its applications for simulation, knowledge will be summarized and summed in order to consolidate the basic
13、knowledge of communications for the After the individual to lay a foundation to study and work. 2 The basic principles of spread spectrum communication 2.1 The definition of spread spectrum communication The so-called spread spectrum communications, can be simply expressed as follows:Spread spectrum
14、 communication technology is a means of information transmission,Share some of its signal bandwidth is much larger than the minimum mass of information necessary bandwidth；The expansion of the band through a separate code sequence to complete, using the method of coding and modulation to achieve, wi
15、th the mass of information has nothing to do；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 an
16、y information needs to a certain bandwidth, as the information bandwidth.For example, the human voice information bandwidth of 300Hz - 3400Hz, television image information bandwidth of MHz.In order to make full use of - 3 - frequency resources, which are roughly the same as far as possible the signa
17、l bandwidth to transmit information.In the radio communication bandwidth RF signals with the mass of information is comparable to the bandwidth.Such as the AM signal used to transmit voice messages, voice messages of their bandwidth for twice the bandwidth；Television broadcasting RF signal bandwidth
18、 is only the video signal bandwidth more than doubled.These are among the narrow-band communications.General FM signal, or pulse code modulation signals, their bandwidth and the information ratio of bandwidth to only a few dozen.Spread spectrum communication signals and information bandwidth than th
19、e bandwidth of up to 100 - 1000, belonging to broadband communications.Why use such a wide-band signal to transmit information? Do not waste valuable resources in the frequency of it? 2)The use of spread-spectrum code sequence modulation signal approach to broadening the spectrum. We know that in ti
20、me limited signal, its spectrum is infinite.For example, very narrow pulses, the spectrum is very wide.Signal bandwidth is inversely proportional to its approximate duration.1 microsecond pulse bandwidth is about 1MHz.Therefore, if the use of limited and narrow pulse sequence has been modulated by t
21、he mass of information it may give rise to very broad-band signal.As described in the following direct sequence spread spectrum system is the method used to obtain spread spectrum signals. This very narrow pulse sequences, the code rate is very high, as the spreading code sequence.Should be noted he
22、re that the spreading codes used by the mass and sequence data is not relevant, that is to say it and in general the same sinusoidal carrier signal, will not affect the transparency of information transmission.Sequence spread-spectrum code signals only from the expansion of the role of the spectrum.
23、 3)In the receiving end to use of the relevant despreading demodulator. As the narrow-band communications in general have been transferred signal demodulation receiver have to be to restore the mass of information.In spread spectrum communications receiver and transmitter used the same spread spectr
24、um code sequence spread spectrum signals received by the relevant demodulation, the restoration of the mass of information.In other words, this correlation despreading demodulation role to play.That is, to expand beyond the original signal is restored by the mass of information. This narrow-band information in the originator to expand into the broadband signal, and in the close-end solution will expand its narrow-band information into the process, will bring a
