【正文】 he system. Easy to use the same frequency, improving the wireless spectrum utilization. Wireless spectrum is very valuable,although longwave microwave have to be exploited, and still can not meet the needs of munity. To this end, countries around the world are designed spectrum management, users can only use the frequency applications,rely on the channel to prevent the division between the channel interference. Due to the use of spreadspectrum munication related receive this hightech,low signal output power(“a W,as a general100mW),and will work in the channel noise and thermal noise in the background,easy to duplicate in the same area using the same frequency,can now all share the same narrowband frequency munication resources. Spreadspectrum munication is digital munication,particularly for digital voice and data transmission with their own encryption, only in the same PN code munication between users, is good for hiding and confidential in nature, facilitating munication business. Easy to use spreadspectrum CDMA munications, voice pression and 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。 擴展頻譜的方式主要有一下幾種：直接序列擴頻（ DSSS）使用高速偽隨機碼對要傳輸?shù)牡退俾蕯?shù)據(jù)進行擴頻調(diào)制；跳頻系統(tǒng)則采用偽隨機碼控制載波頻率在一個更寬的頻帶內(nèi)變化；跳時則是數(shù)據(jù)傳輸時隙是偽隨機的；線性調(diào)頻系統(tǒng)中的頻率擴展則是一個線性變化的過程。 抗多徑干擾能力強，增加了系統(tǒng)的可靠性。 碼分多址 碼分多址（ CDMA）是一種用于各種無線通信技術的信道接入方法。 擴頻 CDMA 的特點 大多數(shù)調(diào)制方案都盡量減少信號的帶寬，因為帶寬是有限的資源。干擾信號可以傳播其能量在信號的整個帶寬或者信號的整個帶寬的一部分。換句話說，只要在多徑信道產(chǎn)生的至少一個芯片的延遲，多徑信號將到達接收機。在 CDMA 系統(tǒng)中，在相同的頻率可以在每個小區(qū)中使用的，因為所使用的偽隨機碼會進行信道化。相比之下， CDMA 系統(tǒng)中使用的軟切換，這是不可檢測的，并提供了更可靠和更高質(zhì)量的信號。發(fā)展到現(xiàn)在，擴頻技術和理論已經(jīng)趨于完善，主要應從系統(tǒng)的角度考慮總體性能，且與其他新技術結(jié)合使用。然而，必須得對 不同的偽隨機序列進行規(guī)劃，以確保從一個小區(qū)接收到的信號不與來自相鄰小區(qū)的信號相關。 偽隨機碼的相關特性是這樣的，這稍微的延遲會導致多路徑出現(xiàn)與預期不相關的信號，因此，它會被忽略。由于窄帶干擾只影響擴頻信號的一小部分，它可以很容易地通過陷波濾波，沒有多少信息損失就可以將它除去。這樣做的最初原因之一是軍事上的應用，包括指導和通信系統(tǒng)。 在數(shù)據(jù)通信中有一種想法是允許多個發(fā)射機同時發(fā)送的信息通過信號通信 信道。無線頻譜十分寶貴，雖然從長波、微波都已得到開發(fā)利用，仍然滿足不了社會的需求。 衡量擴頻系統(tǒng)最重要的一個指標是擴頻增益，又稱為處理增益。 Frequencyhopping system using pseudorandom code to control the carrier frequency in a wider band of the change。 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