【正文】 of the power is very small, signal submerged in noise, are generally not easily found, and would like to further detection signal parameters ( such as pseudorandom coded sequence ) is more difficult, so that its concealment. Furthermore, due to the spread spectrum signal has very low power spectral density, the current use of the narrowband munication interference is very small. realize the code division multiple access Spread spectrum munication improves the antiinterference performance, but paid the occupied bandwidth costs, if many users share the bandwidth, can greatly improve the utilization rate of frequency band. Due to the spread spectrum munication in presence of the spreading code sequence spread spectrum modulation, make full use of all sorts of different type of code spreading code sequences between excellent autocorrelation and crosscorrelation properties, at the receiving end using correlation detection technology for despreading, are assigned to different user code case can distinguish between different user signal, extraction the useful signal. Thus, in a wide frequency band is many user can also call and no mutual interference. multipath interference In a wireless munication in various frequency bands, longterm since, multipath interference is always a difficult problem to solve. In the past the narrow band munication, using two methods to improve the ability of anti multipath interference : one is to put the most useful signal is separated, the exclusion of other paths of the interference signal, which uses diversity / receiving technology。 television broadcasting RF signal bandwidth is only the video signal bandwidth doubling. These all belong to the narrow band munication. The FM signal, or pulse code modulated signals, their bandwidth and information bandwidth ratio is also only a few ten. Spread spectrum munication signal bandwidth and bandwidth ratio is as high as 1001000, belonging to the broadband munication. Why use such wide band signal to transmit information? Wouldn39。 bandwidth expansion is through an independent code sequence to plete, with the coding and modulation method, and the transmitted information data independence。 two is related to recovery after treatment into narrowband information data. It is due to the two holding point, make the spread spectrum munication has the following advantages: high anti jamming noise anti multipath fading with the confidentiality of the power spectral density is low, has the nature of concealment and low probability of intercept can be multiple access multiplexing and arbitrary location of high precision measurement Because of the spread spectrum munication technology has the advantages of the United States Army, from 50 time metaphase begins study convenient for military munications, has been the exclusive, widely used in military munication, electronic countermeasure and navigation, measurement and other fields. Until the early 8039。A spread spectrum munication technology spread spectrum munication system overview Spread spectrum munication, namely the spread spectrum munication ( Spread Spectrum Communication ), and optical fiber munication, satellite munication, together known as entering the information age of three big hightech munication transmission method. Spread spectrum munication is to transmit information data by the pseudo random code ( spread spectrum sequence: Spread Sequence ) modulation, realization of spread spectrum and transmission。 receiving end uses the same code demodulator and related treatment, recovery of the original information data. This munication mode and the conventional narrow munication mode are different: one is the information spread spectrum after the formation of broadband transmission。s before being used in civil munication field. In order to meet the growing needs of the civilian munication capacity and the efficient use of spectrum resources, all countries have made in digital cellular mobile munications, mobile satellite munications and future personal munication using spread spectrum technology, spread spectrum technology has been widely used in cellular phones, cordless telephone, microwave munications, wireless data munication, remote sensing, monitoring, alarm system Two spread spectrum munication the basic concept spectrum munications The spread spectrum munication, can be simply expressed as follows: spread spectrum munication technique is a method for transmitting informationType, its 2 signal the band width is far greater than