碼分多址通信系統(tǒng)、擴頻通信外文翻譯-其他專業(yè)-在線瀏覽
2025-03-24 03:02本頁面
【正文】 many other new technologies, more applicable to puter works and digitization of voice,image information transmission. Communication in the most digital circuits, equipment, highly integrated, easy installation, easy maintenance, but also very pact and reliable. The average failure rate no time was very long. Spread spectrum munication system Spread spectrum munication,namely, spread spectrum munications (Spread spectrum munication), with fiberoptic munications,satellite munications,with access to the information age as the three major hightech munications transmission. Spread spectrum munication is to send the information to be pseudorandom data is coded(Spread spectrum sequence: spread sequence) modulation, spread spectrum and then the realization of transmission。 the receiving end is using the same modem code and related processing, the restoration of the original data. Spread spectrum munication system has three main characteristics. (1) Carrier is an unpredictable, or socalled pseudorandom broadband signal. (2) Carrier data bandwidth than the modulation bandwidth is much wilder. (3) 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 highspeed pseudorandom code on to the lowspeed data transmission spread spectrum modulation。 TH is the data transmission time slot is a pseudorandom。 this code makes the spread spectrum signals appear random or have noiselike properties. A receiver cannot demodulate this transmission without knowledge of the pseudorandom sequence used to encode the data. CDMA also resistant to jamming. A jamming signal only has a finite amount of power available to jam the signal. The jammer can either spread its energy over the entire bandwidth of the signal or jam only part of the entire signal. CDMA can also effectively reject narrow band interference. Since narrow band interference affects only a small portion of the spread spectrum signal, it can easily be removed through notch filtering without much loss of information. Convolution encoding and interleaving can be used to assist in recovering this lost data. CDMA signal are also resistant to multipath fading. Since the spread spectrum signal occupies a large bandwidth only a small portion of this will undergo fading due to multipath at any give time. Like the narrow band interference this will result in only a small loss of data and can be overe. Another reason CDMA is resistant to multipath interference is because the delayed versions of the transmitted pseudorandom code, and will thus appear as another user, which is ignored at the receiver. In other words, as long as the multipath channel induces at least one chip of delay, 天 the multipath channel induces at least one chip of delay,the multipath signals will arri
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