【正文】 time and symbol is slightly different, despread still maintains its broad band, and the useful signal will be pressed, the pulse interference, bandwidth will be expanded to B, and the useful signal recovery ( pression ), ensure higher interference, because of the excellent performance of spread spectrum system, the bit error rate is very low, normal conditions can be as low as l010, the worst conditions about 106, can fully meet the domestic system of channel transmission quality requirement. As a result of spread spectrum signal in a relatively wide frequency band was expanded, the unit within the frequency band 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。 bandwidth expansion is through an independent code sequence to plete, with the coding and modulation method, and the transmitted information data independence。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。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 the transmitted information required minimum bandwidth。t that is a waste of valuable frequency resources? using the spread spectrum code sequence modulation way to stretch the signal spectrum. We know, in terms of time limited signal, the spectrum is infinite. For example, a very narrow pulse signal, the spectrum is very wide. Signal frequency band width and its duration is approximately inversely proportional to. 1 microsecond pulse bandwidth is about 1MHz. Therefore, if with limited narrow pulse sequence is transmitted information modulation, can produce very wide band signal. As following the presentation of the direct sequence spread spectrum system is obtained with such a method of spread spectrum signal. This very narrow pulse code sequence, the code rate is very high, known as the spreading code sequences. There needs to be explained is the spreadin