碼分多址通信系統(tǒng)、擴(kuò)頻通信外文翻譯-其他專業(yè)-免費(fèi)閱讀
【正文】 結(jié)束語 擴(kuò)頻通信在發(fā)展的初始階段，就已經(jīng)實(shí)現(xiàn)了理論與技術(shù)上的重大突破，在此之后的發(fā)展過程中主要是 硬件的改善和性能的提高。在每一個小區(qū)內(nèi)可以重復(fù)使用相同的頻率，所以在 CDMA 系統(tǒng)中不需要頻率規(guī)劃 。換句話說，只要在多徑信道引起至少一個芯片的延遲，多徑信號將到達(dá)接收機(jī)，這樣，它們比預(yù)定信號中在時間上移位一個芯片延遲。 CDMA 還可以有效抑制窄帶干擾。然而，擴(kuò)頻技術(shù)用比所需的最小信號帶寬大幾個數(shù)量級的傳輸帶寬。它不應(yīng)該與被用在移動電話標(biāo)準(zhǔn)的要求的 cdmaOne， CDMA2021（ cdmaOne 的的 3G 演進(jìn)）和 WCDMA 相混淆（用于 GSM 的載波 3G標(biāo)準(zhǔn)），它往往被簡稱為 CDMA，并且作為一個潛在的信道接入方法。由于擴(kuò)頻系統(tǒng)中采用的 PN 碼具有很好的自相關(guān)性，互相關(guān)性很弱，不同路徑傳來的信號很容易被分開，并可在時間相位上重新對齊，形成幾路信號功率的疊加，從而改善了接收系統(tǒng)的性能增加了系統(tǒng)的可靠性，易于同頻使用，提高了無線頻譜利用率。幾種方式組合的混合系統(tǒng)也經(jīng)常得到應(yīng)用。 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。 however, planning of the different pseudorandom sequences must be done to ensure that the received signal from one cell does not correlate with the signal from a nearby cell. Since adjacent cell use the same frequencies, CDMA systems have the ability to perform soft handoffs. Soft handoffs allow the mobile telephone to munication simultaneously with two or more cells. The best signal quality in selected until the handoff is plete. This is different from hard handoffs utilized in other cellular systems. In a hard handoff situation, as the mobile telephone approaches a handoff, signal strength may vary abruptly. In contrast, CDMA systems use the soft handoff, which is undetectable and provides a more reliable and higher quality signal. Concluding remarks spreadspectrum technology in the initial stages of development, it has bee a theory and a major technological breakthrough. Later in the development process is the improvement and hardware performance improved. Development to the present,spreadspectrum technology and the theory has been almost perfect,mainly from the point of view of overall performance, and the other new technology applications. Therefore, the application has been driven by the development of spreadspectrum technology is a power driving force, the future wireless munication systems, such as mobile munication. Wireless LAN, global personal munications, spreadspectrum technology will certainly play an important role. 譯文正文 擴(kuò)頻通信，即擴(kuò)展頻譜通信（ Spread spectrum munication)，它與光纖通信、衛(wèi)星通信，一同譽(yù)為進(jìn)入信息時代的三大高技術(shù)通信傳輸方式，擴(kuò)頻通信是將待傳送的信息數(shù)據(jù)被偽隨機(jī)碼調(diào)制，實(shí)現(xiàn)頻譜擴(kuò)展后再傳輸；接收端則采用相同的編碼進(jìn)行解調(diào)及相關(guān)處理，恢復(fù)原始信息數(shù)據(jù)。 擴(kuò)頻技術(shù)的優(yōu)越性 抗干擾能力強(qiáng)，誤碼率低，如上所述，擴(kuò)頻通信系統(tǒng)由于在發(fā)送端擴(kuò)展信號頻譜，在接收端解擴(kuò)還原信號，產(chǎn)生擴(kuò)頻增益，從而大大提高了抗干擾容限。擴(kuò)頻通信容易采用碼分多址、
范文總結(jié)相關(guān)推薦
鄂ICP備17016276號-1