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瀏覽歷史

3G知識普及
ECSHOP / 2009-05-18

3G知識普及

3G,全稱為3rd Generation,中文含義就是指第三代數字通信。

  1995年問世的第一代模擬制式手機(1G)只能進行語音通話;

  1996到1997年出現的第二代GSM、TDMA等數字制式手機(2G)便增加了接收數據的功能,如接收電子郵件或網頁;

  3G不是2009年誕生的,它是上個世紀的產物,而早在2007年國外就已經產生4G了,而中國也於2008年成功開發出中國4G,其網絡傳輸的速度可達到每秒鐘2G,也就相當於下一部電影只要一秒鐘。在上世紀90年末的日韓電影如《我的野蠻女友》中,女主角使用的可以讓對方看見自己的視頻電話,就是屬於3G技術的重要運用之一。日韓等國3G的運用是上世紀末期的事。而目前國外有些地區已經試運行3.5G甚至4G網絡。

  (以下為誤導)2009年問世的第三代(3G)與 前兩代的主要區別是在傳輸聲音和數據的速度上的提升,它能夠在全球範圍內更好地實現無縫漫遊,並處理圖像、音樂、視頻流等多種媒體形式,提供包括網頁瀏 覽、電話會議、電子商務等多種信息服務,同時也要考慮與已有第二代系統的良好兼容性。為了提供這種服務,無線網絡必須能夠支持不同的數據傳輸速度,也就是 說在室內、室外和行車的環境中能夠分別支持至少2Mbps(兆比特/每秒)、384kbps(千比特/每秒)以及144kbps的傳輸速度。(此數值根據 網絡環境會發生變化)。

  3G標準,國際電信聯盟(ITU)目前一共確定了全球四大3G標準,它們分別是WCDMA、CDMA2000和TD-SCDMA和WiMAX。

3G標準  國際電信聯盟(ITU)在2000年5月確定W-CDMA、CDMA2000、TD-SCDMA以 及WiMAX四大主流無線接口標準,寫入3G技術指導性文件《2000年國際移動通訊計劃》(簡稱IMT—2000)。 CDMA是Code Division Multiple Access (碼分多址)的縮寫,是第三代移動通信系統的技術基礎。第一代移動通信系統采用頻分多址(FDMA)的模擬調制方式,這種系統的主要缺點是頻譜利用率低, 信令幹擾話音業務。第二代移動通信系統主要采用時分多址(TDMA)的數字調制方式,提高了系統容量,並采用獨立信道傳送信令,使系統性能大大改善,但 TDMA的系統容量仍然有限,越區切換性能仍不完善。CDMA系統以其頻率規劃簡單、系統容量大、頻率復用系數高、抗多徑能力強、通信質量好、軟容量、軟 切換等特點顯示出巨大的發展潛力。下面分別介紹一下3G的幾種標準:


  
(1) W-CDMA


  也稱為WCDMA,全稱為Wideband CDMA,也稱為CDMA Direct Spread,意為寬頻分碼多重存取,這是基於GSM網發展出來的3G技術規範,是歐洲提出的寬帶CDMA技術,它與日本提出的寬帶CDMA技術基本相 同,目前正在進一步融合。W-CDMA的支持者主要是以GSM系統為主的歐洲廠商,日本公司也或多或少參與其中,包括歐美的愛立信、阿爾卡特、諾基亞、 朗訊、北電,以及日本的NTT、富士通、夏普等廠商。 該標準提出了GSM(2G)-GPRS-EDGE-WCDMA(3G)的演進策略。這套系統能夠架設在現有的GSM網絡上,對於系統提供商而言可以較輕易 地過渡,但是GSM系統相當普及的亞洲對這套新技術的接受度預料會相當高。因此W-CDMA具有先天的市場優勢。


  
(2)CDMA2000


  CDMA2000是由窄帶CDMA(CDMA IS95)技術發展而來的寬帶CDMA技術,也稱為CDMA Multi-Carrier,它是由美國高通北美公司為主導提出,摩托羅拉、Lucent 和後來加入的韓國三星都有參與,韓國現在成為該標準的主導者。這套系統是從窄頻CDMAOne數字標準衍生出來的,可以從原有的CDMAOne結構直接升 級到3G,建設成本低廉。但目前使用CDMA的地區只有日、韓和北美,所以CDMA2000的支持者不如W-CDMA多。不過CDMA2000的研發技術 卻是目前各標準中進度最快的,許多3G手機已經率先面世。該標準提出了從CDMA IS95(2G)-CDMA20001x-CDMA20003x(3G)的演進策略。CDMA20001x被稱為2.5代移動通信技術。 CDMA20003x與CDMA20001x的主要區別在於應用了多路載波技術,通過采用三載波使帶寬提高。目前中國電信正在采用這一方案向3G過渡,並已建成了CDMA IS95網絡。


  
(3)TD-SCDMA


  全稱為Time Division - Synchronous CDMA(時分同步CDMA),該標準是由中國大陸獨自制定的3G標準,1999年6月29日,中國原郵電部電信科學技術研究院(大唐電信)向ITU提出。該標準將智能無線、同步CDMA和軟件無 線電等當今國際領先技術融於其中,在頻譜利用率、對業務支持具有靈活性、頻率靈活性及成本等方面的獨特優勢。另外,由於中國內的龐大的市場,該標準受到各 大主要電信設備廠商的重視,全球一半以上的設備廠商都宣布可以支持TD—SCDMA標準。 該標準提出不經過2.5代的中間環節,直接向3G過渡,非常適用於GSM系統向3G升級。


  
(4)WiMAX


  WiMAX 的全名是微波存取全球互通(Worldwide Interoperability for Microwave Access),又稱為802·16無線城域網,是又一種為企業和家庭用戶提供“最後一英裏”的寬帶無線連接方案。將此技術與需要授權或免授權的微波設備 相結合之後,由於成本較低,將擴大寬帶無線市場,改善企業與服務供應商的認知度。2007年10月19日,國際電信聯盟在日內瓦舉行的無線通信全體會議 上,經過多數國家投票通過,WiMAX正式被批準成為繼WCDMA、CDMA2000和TD-SCDMA之後的第四個全球3G標準。

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