外文翻譯---無線移動數(shù)據(jù)業(yè)務(wù)及其發(fā)展趨勢.doc (2)

1、<p>　　無線移動數(shù)據(jù)業(yè)務(wù)及其發(fā)展趨勢</p><p>　　摘 要：本文首先介紹了蜂窩數(shù)字分組數(shù)據(jù)(CDPD)業(yè)務(wù)，然后介紹了GSM移動數(shù)據(jù)業(yè)務(wù)，并對幾種主流業(yè)務(wù)進(jìn)行了比較和分析，最后得出GSM移動數(shù)據(jù)業(yè)務(wù)的發(fā)展趨勢。</p><p><b>　　一、前言</b></p><p>　　無線移動數(shù)據(jù)業(yè)務(wù)是無線數(shù)據(jù)中心與主機(jī)或其他無線

2、終端之間采用無線連接，通過無線電波傳遞數(shù)據(jù)的一種通信方式。它是移動通信和數(shù)據(jù)通信的結(jié)合物，是當(dāng)前信息產(chǎn)業(yè)發(fā)展的熱點(diǎn)。高速、有效、可靠的無線數(shù)據(jù)傳輸技術(shù)的成熟，以及便攜式計(jì)算機(jī)和各種數(shù)據(jù)終端的處理能力與通信功能的日益完善，為無線移動數(shù)據(jù)通信技術(shù)的發(fā)展創(chuàng)造了有利條件。</p><p>　　近幾年，無線移動數(shù)據(jù)業(yè)務(wù)得到了迅速發(fā)展。移動通信和數(shù)據(jù)通信的融合將促進(jìn)無線移動互聯(lián)網(wǎng)和E-mail等更為廣泛的應(yīng)用，也必將促進(jìn)第二

3、代移動通信系統(tǒng)向第三代的演進(jìn)。1994年4月成立了蜂窩數(shù)字分組數(shù)據(jù)(CDPD)論壇，這是一個(gè)民間組織，它由多家運(yùn)營商、系統(tǒng)集成商、設(shè)備制造商、軟件及應(yīng)用開發(fā)商等共同發(fā)起創(chuàng)建的。制定了CDPD的技術(shù)規(guī)范，推動了CDPD技術(shù)和市場發(fā)展。1995年以后，我國移動通信在數(shù)字化和市場競爭的推動下，進(jìn)入了以GSM為主的快速發(fā)展軌道。而GSM無線數(shù)據(jù)通信使得人們不受空間、地域的限制，隨時(shí)隨地獲取所需的信息，可以在移動中收發(fā)電子郵件、收到傳真、訪問In

4、ternet等業(yè)務(wù)，這是數(shù)據(jù)通信技術(shù)和移動通信技術(shù)的結(jié)合。對GSM數(shù)據(jù)通信業(yè)務(wù)，人們又在諸多方面進(jìn)行了改進(jìn)、調(diào)整，例如提供消息系統(tǒng)、電路交換型和分組交換型移動數(shù)據(jù)的功能等等，即從最初的電路型數(shù)據(jù)業(yè)務(wù)到高速電路交換數(shù)據(jù)(HSCSD)業(yè)務(wù)進(jìn)而到通用分組無線業(yè)務(wù)(GPRS)、增強(qiáng)型分組(EDGE)業(yè)務(wù)和IMT2000分組型數(shù)據(jù)業(yè)務(wù)。下面對不同類型的數(shù)據(jù)業(yè)務(wù)進(jìn)行介紹。</p><p>　　二、蜂窩數(shù)字分組數(shù)據(jù)(CDPD)

5、業(yè)務(wù)</p><p>　　1．CDPD的概念 ·</p><p>　　CDPD是建立在TCP／IP基礎(chǔ)上的一種開放系統(tǒng)結(jié)構(gòu)，采用分組數(shù)據(jù)交換方式，將開放式接口。高傳輸速度、用戶單元確定、空中鏈路加密、空中數(shù)據(jù)加密、壓縮數(shù)據(jù)交錯(cuò)與重發(fā)以及IP尋址模式結(jié)合在一起，提供同層網(wǎng)絡(luò)的無縫連接以及多協(xié)議網(wǎng)絡(luò)服務(wù)。</p><p>　　所謂分組數(shù)據(jù)交換，就是將要傳

6、輸?shù)臄?shù)據(jù)按一定長度分組，然后，把來自不同數(shù)據(jù)源的數(shù)據(jù)分組在一條信道上交織地進(jìn)行傳輸。</p><p>　　CDPD系統(tǒng)是基于AMPS蜂窩移動電話系統(tǒng)之上的分組數(shù)據(jù)交換系統(tǒng)，它采用TCP／IP協(xié)議，利用話音信道的間隙傳送數(shù)據(jù)。</p><p>　　2．CDPD系統(tǒng)簡單組成</p><p>　　從網(wǎng)絡(luò)結(jié)構(gòu)上看，一個(gè)CDPD系統(tǒng)由交換機(jī)、基站和網(wǎng)絡(luò)管理系統(tǒng)組成。</

7、p><p>　　(1)CDPD交換機(jī)</p><p>　　主要由分組服務(wù)器和管理服務(wù)器兩部分組成。其中分組服務(wù)器負(fù)責(zé)分組數(shù)據(jù)交換，管理服務(wù)器負(fù)責(zé)用戶賬戶管理以及記費(fèi)信息管理。</p><p><b>　　(2)基站</b></p><p>　　每個(gè)基站上的信道板為移動終端提供一個(gè)19．2kbps的空中接人，使移動終端進(jìn)行全雙

8、工分組數(shù)據(jù)傳輸。同時(shí)它也負(fù)責(zé)頻譜檢測、頻率管理。它通過一根64kbps幀中繼與交換機(jī)相連接。</p><p><b>　　(3)網(wǎng)絡(luò)管理系統(tǒng)</b></p><p>　　負(fù)責(zé)對整個(gè)CDPD網(wǎng)絡(luò)進(jìn)行管理，并能進(jìn)行遠(yuǎn)程設(shè)置和修改。由于CDPD是基于TCP／IP發(fā)展起來的，因而它可以通過Internet、X．25、DDN、電話網(wǎng)和ISDN很容易地與其他網(wǎng)絡(luò)相連。</p

9、><p>　　3．CDPD系統(tǒng)的主要技術(shù)參數(shù)</p><p>　　頻段：824—849MHz，869--894MHz</p><p><b>　　調(diào)制方式：GMSK</b></p><p>　　RF速率：19．2kbps</p><p>　　基站發(fā)謝功率：45W(連續(xù)可調(diào))</p>&l

10、t;p>　　基站接受靈敏度：—116dBm</p><p>　　頻道間隔：30kHz</p><p>　　信道占用方式：DSMA／CD</p><p><b>　　載干比：17dB</b></p><p>　　終端發(fā)射功率：0．6--4W</p><p>　　終端接收靈敏度：—113dBm&

11、lt;/p><p>　　4．CDPD的應(yīng)用領(lǐng)域</p><p>　　目前，CDPD主要用于小范圍內(nèi)的移動通信系統(tǒng)。特別適用于用戶點(diǎn)多、分布面廣，移動中短信息使用頻次密的場合。主要應(yīng)用領(lǐng)域有：</p><p><b>　　(1)金融交易</b></p><p>　　在商業(yè)金融交易領(lǐng)域，如持卡購物、證券交易、電子銀行、金融保險(xiǎn)、

12、POS系統(tǒng)等，都可用CDPD系統(tǒng)。</p><p><b>　　(2)交通運(yùn)輸</b></p><p>　　在交通運(yùn)輸行業(yè)，如汽車調(diào)度、路由導(dǎo)引、車流量測控、車輛GPS自動定位跟蹤、汽車防盜、出租車移動刷卡消費(fèi)等場合，可CDPD系統(tǒng)。</p><p>　　(3)遙測與遠(yuǎn)程監(jiān)控</p><p>　　在城市供水、供電、煤氣、

13、環(huán)保、銀行無線ATM、各類工業(yè)控制、醫(yī)療保健等場合也可以用CDPD系統(tǒng)實(shí)現(xiàn)遙測和過程監(jiān)控，以提高工作效率。CDPD還可以滿足對各類營業(yè)場合的財(cái)務(wù)、采購以及住宅區(qū)的安全防范需求。</p><p><b>　　(4)移動辦公</b></p><p>　　現(xiàn)代生活的許多工作和業(yè)務(wù)都需要在辦公室以外的地方進(jìn)行，如交警、工商稅務(wù)人員、新聞記者、律師、房地產(chǎn)代理、保險(xiǎn)經(jīng)濟(jì)、銀行經(jīng)

14、理、行政官員等，他們需要利用移動數(shù)據(jù)終端查詢主機(jī)數(shù)據(jù)庫，進(jìn)行實(shí)時(shí)數(shù)據(jù)交換、訪問及控制，實(shí)現(xiàn)新聞采訪的文件傳遞、現(xiàn)場辦公服務(wù)等。</p><p>　　三、移動數(shù)據(jù)業(yè)務(wù)及其發(fā)展趨勢</p><p><b>　　1．消息系統(tǒng)</b></p><p>　　現(xiàn)在GSM移動通信系統(tǒng)已經(jīng)能夠提供短消息服務(wù)功能，兩個(gè)GSM手機(jī)之間可以發(fā)</p>

15、<p>　　送、接收中文短消息。移動通信網(wǎng)與Internet連接后，手機(jī)用戶可以從Internet上獲取信息。如若運(yùn)營商與信息內(nèi)容提供商合作，用戶可以得到豐富的信息服務(wù)，如股市行情、經(jīng)濟(jì)新聞、旅游信息、交通情況等。這樣，利用短消息系統(tǒng)也可以形成一個(gè)個(gè)人的移動信息</p><p>　　2．電路型數(shù)據(jù)業(yè)務(wù)和分組型數(shù)據(jù)業(yè)務(wù)</p><p>　　GSM移動數(shù)據(jù)業(yè)務(wù)是這樣劃分的。GSM第一

16、階段提出的9600bps以下數(shù)據(jù)業(yè)務(wù)及phase2+階段提出的HSCSD都屬于電路型數(shù)據(jù)業(yè)務(wù)。Phase2+階段提出的GPRS、EDGE以及IMT-2000，則屬于分組型數(shù)據(jù)業(yè)務(wù)。后者相對于前者具有很顯著的優(yōu)越性，</p><p>　　兩者對比如表1所示。</p><p><b>　　(1)HSCSD</b></p><p>　　HSCSD即高

17、速電路交換數(shù)據(jù)。它是一種新的信道編碼技術(shù)，把一個(gè)時(shí)隙9 600bps的傳輸速率提高到14．4kbm。即只使用一個(gè)時(shí)隙用戶傳輸數(shù)率即可提高50％。HSCSD還允許以“時(shí)隙捆綁”方式進(jìn)行數(shù)據(jù)傳輸，最高的“四時(shí)隙捆綁”達(dá)到57．6kbm，相當(dāng)于一個(gè)ISDNB信道的速率。在數(shù)據(jù)業(yè)務(wù)中，大部分?jǐn)?shù)據(jù)從基站流向移動電話。上下行數(shù)據(jù)傳輸可以采用不同的速率，上行時(shí)隙一般需求較少(在數(shù)據(jù)業(yè)務(wù)中，大部分?jǐn)?shù)據(jù)從基站流向移動電話)，可以為下行鏈路提供更多的空閑時(shí)

18、隙。</p><p>　　HSCSD業(yè)務(wù)，屬電路型數(shù)據(jù)業(yè)務(wù)，電路型數(shù)據(jù)業(yè)務(wù)可以應(yīng)用在PLMN內(nèi)部以及PLMN和PSTN／ISDN／PSPDN之間，其中和PSPDN的互通是通過PSTNZISDN進(jìn)行的。不同的承載業(yè)務(wù)類型所對應(yīng)的傳輸路徑是不同的，相應(yīng)地所對應(yīng)的組網(wǎng)形式也不同。HSCSD實(shí)際上是一種增強(qiáng)型承載數(shù)據(jù)業(yè)務(wù)，本質(zhì)上與承載數(shù)據(jù)業(yè)務(wù)無多大區(qū)別。HSCSD硬件上也易于實(shí)施，無需改變目前GSM網(wǎng)絡(luò)的硬件結(jié)構(gòu)。<

19、;/p><p><b>　　(2)GPRS</b></p><p>　　GPRS即通用分組無線業(yè)務(wù)，屬分組型數(shù)據(jù)業(yè)務(wù)。它與電路型數(shù)據(jù)業(yè)務(wù)有本質(zhì)區(qū)別：電路型數(shù)據(jù)業(yè)務(wù)必須先建立一個(gè)呼叫并始終占據(jù)該呼叫信道直至呼叫結(jié)束，它并不考慮所占用的信道是否正在傳輸信息或數(shù)據(jù)；分組型數(shù)據(jù)—業(yè)務(wù)則無須先建立呼叫，只是在需要傳輸數(shù)據(jù)的時(shí)候利用空閑信道，數(shù)據(jù)傳輸完立即釋放，并不長久地占用信道。顯

20、然，GPRS確實(shí)是提供移動數(shù)據(jù)業(yè)務(wù)的上好選擇。主要原因有：①由于采用分組技術(shù)，可以有數(shù)據(jù)傳輸時(shí)才占用資源，從而使網(wǎng)絡(luò)資源利用率大大提高。而且由于采用分組技術(shù)，可以做到按實(shí)際傳輸?shù)臄?shù)據(jù)量進(jìn)行計(jì)費(fèi)，從而使計(jì)費(fèi)方式更科學(xué)合理。②由于采用多時(shí)隙聯(lián)合應(yīng)用和高速編碼方案，GPRS可提供115．2bps的數(shù)據(jù)速率；（3）GPRS支持IP協(xié)議和X．25協(xié)議。這就是說GPRS不僅支持基于IP的Internet業(yè)務(wù)，也支持傳統(tǒng)的基于X．25協(xié)議的分組數(shù)據(jù)業(yè)

21、務(wù)。</p><p>　　GPRS的系統(tǒng)結(jié)構(gòu)如圖1所示。</p><p>　　圖1中，現(xiàn)有GSM網(wǎng)絡(luò)增加GPRS功能，除新增SGSN(服務(wù)GPRS支撐點(diǎn))和GGSN(關(guān)口GPRS支撐點(diǎn))等網(wǎng)絡(luò)節(jié)點(diǎn)外，還必須對網(wǎng)上設(shè)備進(jìn)行升級</p><p><b>　　(a)BTS升級 </b></p><p>　　一般不需要升級硬件，

22、但必須進(jìn)行軟件升級，以支持GPRS新增的邏輯信道和4種新</p><p>　　的編碼方案( CSl，CS2，CS3，CS4，其中CS3和CS4在第一階段可不支持)以及Abis 接口規(guī)程。</p><p><b>　　(b)BSC升級</b></p><p>　　硬件須增加分組控制單元PCU，以支持GPRS的Gb接口協(xié)議和其他GPRS通信協(xié)議 (

23、BS~P,RLC／MAC等)，除此以外還要升級無線資源管理部分和操作維護(hù)部分的軟件。</p><p>　　(c)MSC／VLR升級移動性管理軟件，以支持GPRS和IMSI Attach ／detach、組合的LA／RA更新等功能；增加經(jīng)過GPRS進(jìn)行CS呼叫的Paging；增加Gs接口(BSSAP+)。</p><p>　　可見GPRS是在GSM系統(tǒng)上通過GPRS網(wǎng)絡(luò)來提供分組交換業(yè)務(wù)，數(shù)

24、據(jù)速率達(dá)</p><p>　　115．2bps(其理論最大值是171．2bps)，保證了更大數(shù)據(jù)的傳送，更快的因特網(wǎng)接人，可以使終端同時(shí)進(jìn)行話音通信業(yè)務(wù)和數(shù)據(jù)通信業(yè)務(wù)，支持各類多媒體業(yè)務(wù)，如圖像，視頻等。</p><p>　　GPRS的應(yīng)用主要分為面向個(gè)人用戶的橫向應(yīng)用和面向集團(tuán)用戶的縱向應(yīng)用兩種。對于橫向應(yīng)用，GPRS可提供網(wǎng)上沖浪，E-mail、文件傳輸、數(shù)據(jù)庫查詢、增強(qiáng)型短消息等業(yè)務(wù)

25、。對于縱向應(yīng)用GPRS可提供以下幾類應(yīng)用：</p><p>　　·運(yùn)輸業(yè)：車輛及智能調(diào)度；</p><p>　　·經(jīng)融、證券和商業(yè)：無線POS、無線ATM、流動銀行等；</p><p>　　·公共安全業(yè)：隨時(shí)隨地接人遠(yuǎn)程數(shù)據(jù)庫；</p><p>　　·遙測、遙感、遙控：如氣象、水文系統(tǒng)收集數(shù)據(jù)，對災(zāi)害進(jìn)

26、行遙測和告警，遠(yuǎn)程操作；</p><p>　　·提供VPN業(yè)務(wù)，使企業(yè)員工能夠隨時(shí)隨地與總部保持聯(lián)系，降低公司建設(shè)自己的廣域網(wǎng)的成本；</p><p>　　還能提供種類繁多、，功能強(qiáng)大的以GPRS承載業(yè)務(wù)為基礎(chǔ)的網(wǎng)絡(luò)應(yīng)用業(yè)務(wù)和基于WAP的各種應(yīng)用。</p><p><b>　　(3)EDGE</b></p><p&

27、gt;　　GPRS的數(shù)據(jù)傳輸速率已經(jīng)達(dá)到了115．2bps，但對于一些如視頻信號的傳輸，這個(gè)速率還是太低。因此，在GPRS的基礎(chǔ)上，EDGE將原來GSM的四相調(diào)制改為八相調(diào)制，使每個(gè)信道的傳輸速率由14．4bps提高到48bps。通過多時(shí)隙捆綁，EDGE的數(shù)據(jù)速率最高達(dá)到384bps，已經(jīng)達(dá)到了ITU規(guī)定的第三代移動通信系統(tǒng)無線傳輸能力的最低限度。</p><p>　　在GPRS網(wǎng)絡(luò)的基礎(chǔ)上引入EDGE，從經(jīng)濟(jì)上

28、是十分合理的。因?yàn)樵黾覧DGE功能只要升級BSS即可，網(wǎng)絡(luò)部分仍使用GPRS網(wǎng)絡(luò)實(shí)體。對于BBS，其中BSC只須升級無線資源管理部分的軟件，BTS除軟件升級外，還要進(jìn)行部分硬件的升級。這種升級不論是從技術(shù)上還是從工程上都是非常可行的。因?yàn)镋DGE的應(yīng)用基點(diǎn)被定義在TDMA的時(shí)隙上，即BTS任一載波的任一時(shí)隙支持EDGE業(yè)務(wù)，其他時(shí)隙不變。因此，在原有GSM的BTS平臺上，簡單的增加新的設(shè)備模塊便可使現(xiàn)有網(wǎng)絡(luò)同時(shí)支持GSM傳統(tǒng)業(yè)務(wù)、GPR

29、S和EDGE高速數(shù)據(jù)業(yè)務(wù)。再進(jìn)一步，如果我們把EDGE的應(yīng)用基點(diǎn)定義在每一個(gè)TRX上，BTS設(shè)備硬件升級將更為方便，因?yàn)檫@時(shí)只須更換與調(diào)制解調(diào)有關(guān)的電路板。這樣不論是改造已有的BTS，還是擴(kuò)容新增BTS，網(wǎng)絡(luò)升級都相當(dāng)平滑。</p><p>　　(4)IMT-2000</p><p>　　1TU在1985年提出了未來陸地移動通信系統(tǒng)即FPLMTS。1992年世界無線電行政大會(WARC)將

30、其頻率定在2000MHz，計(jì)劃在2000年左右進(jìn)入商用。在一些國家的建議下，1996年將FPLMTS正式更名為IMT-2000。它能夠?qū)崿F(xiàn)用戶手持一機(jī)走遍全球。而且無論用戶漫游到哪里，都能夠得到相同的服務(wù)業(yè)務(wù)，使用戶毫無察覺?？梢苑奖愕卦谝苿迎h(huán)境下上網(wǎng)漫游、收發(fā)Email、收看交互式新聞，實(shí)現(xiàn)移動環(huán)境下的虛擬辦公等等。</p><p>　　IMT-2000的主要業(yè)務(wù)特征是支持IP和高速數(shù)據(jù)業(yè)務(wù)。IMT-2000的

31、2Mbm的接人帶寬使得IMT-2000可以向用戶提供真正的移動多媒體業(yè)務(wù)。同時(shí)由于IMT-2000支持業(yè)務(wù)的上行和下行的非對稱傳輸，支持以傳輸數(shù)據(jù)量作為收費(fèi)依據(jù)，使得無線數(shù)據(jù)業(yè)務(wù)得到更為廣泛的應(yīng)用。</p><p>　　3．無線移動數(shù)據(jù)業(yè)務(wù)的發(fā)展</p><p>　　無線移動數(shù)據(jù)業(yè)務(wù)的發(fā)展有一個(gè)過程，以保證2G向3G的平滑過渡。圖2所示為GSM移動數(shù)據(jù)業(yè)務(wù)的發(fā)展趨勢。圖中，HSCSD到GP

32、RS是一個(gè)質(zhì)的飛躍，它是由電路型數(shù)據(jù)業(yè)務(wù)轉(zhuǎn)變?yōu)榉纸M型數(shù)據(jù)業(yè)務(wù)。EDGE分組型數(shù)據(jù)業(yè)務(wù)只是GPRS的升級。</p><p><b>　　四、結(jié)束語</b></p><p>　　從GSM到3G，各種數(shù)據(jù)業(yè)務(wù)之間的$敬如l是大家關(guān)心最多的問題。其實(shí)，從設(shè)備上分析，GSM到3G根本不存在平滑過渡的可能。首先從核心網(wǎng)來看，GSM核心網(wǎng)是以電路交換為基礎(chǔ)的，而第三代系統(tǒng)核心網(wǎng)絡(luò)是

33、基于包交換的，平滑過渡也很不現(xiàn)實(shí)；從無線技術(shù)方面上看，GSM采用的是TDMA制式，而第三代系統(tǒng)采用的是CDMA，更無平滑過渡可言。因此，所謂的“平滑過渡”只能寄希望于核心網(wǎng)中的不同系統(tǒng)互聯(lián)，同時(shí)使終端設(shè)備同時(shí)支持GSM和第三代無線技術(shù)。因此，“平滑過渡”只有在業(yè)務(wù)上才是有現(xiàn)實(shí)意義的。第三代系統(tǒng)的一個(gè)突出特征是提供寬帶數(shù)據(jù)業(yè)務(wù)和多媒體業(yè)務(wù)，用戶認(rèn)同接收這些業(yè)務(wù)要有相當(dāng)長的時(shí)間。為了在起用第三代移動通信系統(tǒng)時(shí)，用戶對新業(yè)務(wù)有更多的了解和認(rèn)可

34、，在GSM網(wǎng)絡(luò)中建設(shè)GPRS甚至EDGE，提供寬帶數(shù)據(jù)業(yè)務(wù)，培養(yǎng)用戶群，是一個(gè)很好的選擇。移動數(shù)據(jù)業(yè)務(wù)的發(fā)展有一個(gè)過程，由電路性數(shù)據(jù)業(yè)務(wù)演變?yōu)榉纸M性數(shù)據(jù)業(yè)務(wù)是一個(gè)質(zhì)的飛躍。隨著技術(shù)的不斷發(fā)展，各種移動數(shù)據(jù)通信業(yè)務(wù)的新技術(shù)也會不斷出現(xiàn)，它們在不同時(shí)期和不同的應(yīng)用領(lǐng)域?qū)l(fā)揮各自的作用，共同促進(jìn)全球信息化的進(jìn)步。</p><p>　　Wireless Mobile Data Service and Its Devel

35、opment Trends</p><p>　　Abstract: This paper introduces cellular digital packet data (CDPD)service at first, then describes GSM mobile data service, makes a comparison and analysis of several major services,

36、and finally discusses development trends of GSM mobile data service.</p><p>　　I. Introduction</p><p>　　Wireless mobile data service is a communications method for data transmission through radio

37、 wave with wireless connection between radio data center and mainframe or other radio terminals. It is a combination of mobile communications and data communications, and is a hot point in current development of informat

38、ion industry. The mature of high speed, effective and reliable radio data transmission technology and increasing perfect of processing capability and communications function of portable com</p><p>　　In recen

39、t years, the radio mobile data service gains rapid development. The fusion of mobile communications and data communications will promote more extensive application of radio mobile Internet and E-mail, and must promote th

40、e evolution of the 2G mobile communication system to the 3G system. In April 1994, the Cellular Digital Packet Data (CDPD)Forum was established. This is a civilian organization and was jointly initiated and built by many

41、 operators, system integrators, equipment manufactur</p><p>　　II. CDPD Service</p><p>　　1. CDPD Concept</p><p>　　CDPD is an open system architecture established on the basis of TCP/

42、IP. It uses packet</p><p>　　data switching, and combines open interface, high transmission speed, user unit determination,</p><p>　　air link encryption, air data encryption, compression data int

43、erlacing and retransmission, and IP addressing mode, providing seamless connection of same-layer networks and multi-protocol network service.</p><p>　　The so-called packet data switching is to packet the dat

44、a to be transmitted with certain length, then transmits data packets from different data sources alternatively over one channel.</p><p>　　CDPD system is a packet data switching system based on AMPS cellular

45、mobile telephone</p><p>　　phone system. It uses TCP/IP protocol, and employ gap of voice channel to transmit data.</p><p>　　2. Simple Constitution of CDPD System</p><p>　　From the v

46、iewpoint of network architecture, a CDPD system consists of exchange, base</p><p>　　station and network management system.</p><p>　　(1) CDPD Exchange</p><p>　　CDPD exchange mainly i

47、ncludes two components, packet server and management server.</p><p>　　The packet server is responsible for packet data switching, and the management server is responsible for account management and cost-reco

48、rding information management.</p><p>　　(2) Base Station</p><p>　　Channel plate on each base station provides an air access of 19.2 kbps for mobile terminal</p><p>　　allowing the mob

49、ile terminal to perform full-duplex packet data transmission. Meanwhile, it is also responsible for frequency spectrum detection and frequency management. It is connected to the exchange via a 64 kbps frame-relay line.&l

50、t;/p><p>　　(3) Network Management System</p><p>　　It is responsible for the management of total CDPD network, and can perform remote setting and modification. Because CDPD develops from TCP/IP, it

51、can easily be connected to other networks through Internet, X. 25,DDN, telephone network and ISDN.</p><p>　　3. Major Technical Parameters for CDPD System</p><p>　　Frequency band. 824- 894 MHz, 8

52、69-- 894 MHz</p><p>　　Modulation way: GMSK</p><p>　　RF rate: 19.2 kbps</p><p>　　Base station transmission power: 45 W ( continuously variable)</p><p>　　Base station rec

53、eiving sensitivity: - 116 dBm</p><p>　　Channel interval: 30 kHz</p><p>　　Channel occupation way: DSMA/CD</p><p>　　Cartier/interference ratio: 17 dB</p><p>　　Terminal tr

54、ansmission power:0.6--4 W</p><p>　　Terminal receiving sensitivity: - 113 dBm</p><p>　　4. CDPD Application Fields</p><p>　　At present, CDPD is mainly used for mobile communications s

55、ystems in small area, especially for cases with many user points, wide distribution and frequent short message usage in</p><p>　　motion. Its major application fields are:</p><p>　　(1) Financial

56、Transaction</p><p>　　In commercial and financial transaction areas, such as purchase with card, stock transaction, E-bank, finance and insurance and POS system, CDPD system can be used.</p><p>　

57、　(2) Traffic Transportation</p><p>　　In traffic transportation industry, such as automobile dispatch, routing guidance, vehicle</p><p>　　traffic measurement and control, vehicle GPS positioning

58、and tracking, automobile guard against theft and taxi mobile consumption with card, CDPD can be used.</p><p>　　(3) Telemetry and Remote Monitoring</p><p>　　In cases of city water supply, electri

59、city supply, gas supply, environment protection, bank</p><p>　　radio ATM, various industrial control, medicine and health protection, CDPD can be used to</p><p>　　implement telemetry and process

60、 monitoring to improve working efficiency. CDPD can also</p><p>　　be used in finance and procurement in various operations, and in security and protection requirements for inhabitant area.</p><p&g

61、t;　　(4) Mobile Official Business</p><p>　　In modem life, a lot of work and business need to be conducted outside the office, and</p><p>　　many people, such as pointsmen, industrial and commercia

62、l tax personnel, news reporters,</p><p>　　lawyers, real estate agents, insurance brokers, bank managers and administrative officers, need</p><p>　　to use mobile data terminal to inquire mainfram

63、e data base to perform real-time data exchange, access and control, realizing file transfer for news interview and office business service on the site.</p><p>　　III. GSM Mobile Data Service and Its Developme

64、nt Trends</p><p>　　1. Message System</p><p>　　Current GSM mobile communications system is' able to provide short message service function with transmission and reception of short message in

65、Chinese between two GSM handsets. After mobile network connected to Internet, the handset user can acquires information from Internet. If the operator cooperates with the ICP, the user can acquire abundant information se

66、rvice, such as share-list, economic news, tourism information and traffic situation. Thus, the short message system can be used to form </p><p>　　2. Circuit Type Data Services Packet Type Data Services</p

67、><p>　　GSM mobile data service is divided as follows: both of data service less than 9 600 bps</p><p>　　proposed in GSM phase 1 and HSCSD proposed in phase 2 + belong to the circuit type services;

68、GPRS,EDGE and IMT-2000 proposed in phase 2 + belong to the packet type data service. The latter has evident advantages over the former, and a comparison on both of them is shown in Table 1.</p><p><b>　

69、　(1) HSCSD</b></p><p>　　HSCSD stands for high-speed circuit switched data. It is a new channel encoding technology, and can raise the transmission rate of 9 600 bps for one time-slot to 14.4 kbps. That

70、 is, only using one time-slot, the user transmission rate can rise by 50 %. HSCSD also allows data transmission using "time-slots strapped" method with maximum "4 timeslots strapped" reaching 57.6 kbp

71、s, corresponding to the rate of one ISDN B channel. In the data service, most data flow from base station to mobile telepho</p><p>　　HSCSD service belongs to circuit type data service. The circuit type data

72、service can be</p><p>　　applied inside PLMN and between PLMN and PSTN/ISDN/PSPDN in which the inter communications with PSPDN is performed through PSTN/ISDN. Different loading services correspond to differen

73、t transmission paths with different network forms.</p><p>　　HSCSD actually is an enhanced loading data service, and it has no significant difference with loading data service in nature. HSCSD hardware is eas

74、ily implemented without changing existing hardware structure for GSM network.</p><p><b>　　(2) GPRS</b></p><p>　　GPRS stands for general packet radio service, belonging to packet type

75、 data service. It has essential difference with the circuit type data service. The circuit type data service must at first set up a call and always occupy the call channel until end of the call, and it does not consider

76、whether the channel transmits data or not. On the contrary, the packet type data service need not set up a call at first, and it only uses unoccupied channel when it is necessary to transmit data and does not</p>

77、<p>　　occupy the channel for a long time. Clearly, GPRS exactly is an excellent selection for providing mobile data service. The major reasons are: (1)Due to using packet technology, the resource is only occupied du

78、ring data ~'on, thus greatly improving network utilization factor. Furthermore, due to packet technology can be implemented according to data amount actually transmitted, allowing accounting method to be more scienti

79、fic and reasonable.(2)Due to using multiple time-slot joint application and</p><p>　　System architecture for GPRS is shown in Figure 1.</p><p>　　In Figure 1, existing GSM network adds GPRS funct

80、ion, and in addition to network</p><p>　　nodes, such as newly increased SGSN (service GPRS support node)and GGSN (gateway</p><p>　　GPRS support node) ,devices on the network should be upgraded.&

81、lt;/p><p>　　(a) BTS Upgrade</p><p>　　This upgrade generally does not need hardware upgrade, but should perform soft- ware</p><p>　　upgrade to support logic channel newly added for GPRS

82、, four new encoding schemes (CS1,</p><p>　　CS2, CS3 and CS4, in which CS3 and CS4 need not be supported in phase 1 ) and Abis inter-</p><p>　　face protocol.</p><p>　　(b) BSC Upgrade

83、</p><p>　　The hardware should add packet control unit (PCU) to support Gb interface protocol</p><p>　　and other GPRS communications protocols (BSSGP, RLC/MAC, etc. ). In addition, it should</

84、p><p>　　upgrade the section for radio resource management and software for operation and maintenance section.</p><p>　　(c) MSC/NLR Upgrade</p><p>　　The upgrade includes upgrading mobil

85、e management to support GPRS and IMSI Attach/detach and combined LA/RA update functions; adding Paging to perform CS call via GPRS; Adding Gs interface (B~AP + ).</p><p>　　It can be seen that GPRS provides p

86、acket switching service through GPRS network on</p><p>　　GSM system with data rate reaching 115. 2 kbps (in theory, its maximum value is 171.2 kbps) ,ensuring transmission with higher data rate and quicker I

87、nternet access, and allowing the terminal to perform voice communications service and data communications service simultaneously to support various multimedia services, such as image service and video service.</p>

88、<p>　　The applications of GPRS are mainly divided into two kinds, lateral application oriented</p><p>　　to personal users and longitudinal for group users. For lateral application, GPRS can provide<

89、/p><p>　　many services, such as surging over web, E-mail, file transmission, data base inquiry and enhanced short message. For longitudinal application, GPRS can provide the following kinds of</p><p&

90、gt;　　applications:</p><p>　　~ Transport industry: vehicle and intelligent dispatching;</p><p>　　~ Finance, stock and commerce: radio POS, radio ATM ,mobile bank, etc;</p><p>　　~ Pub

91、lic security industry: access to remote data base at any place and any time;</p><p>　　~Telemetry, remote sensing and remote control: such as data collection for meteorological and hydrological systems, telem

92、etry and warning for disasters, and remote operations;</p><p>　　~ Providing VPN service to allow staff and workers in an enterprise to keep contact with headquarters at any place and any time for reducing co

93、st for the company to construct its own wide area network;</p><p>　　~ In addition, it can provide various powerful network application services on the basis of GPRS loading service and various applications b

94、ased on WAP.</p><p>　　(3) EDGE (Enhanced Data Rates GSM Evolution)</p><p>　　The data transmission rate for GPRS has reached 115.2 kbps, but for transmission of some signal, such as video signal,

95、 this rate is still too low. Therefore, on the basis of GPRS, EDGE will change 4-phase modulation of original GSM to 8-phase modulation, making the transmission rate of each channel rise from 14.4 kbps to 48 kbps. Throug

96、h multiple time-slot strapping, the maximum data transmission rate for EDGE can reach 384 kbps, already reach in the lowest limit of radio transmission capability</p><p>　　It is quite reasonable economically

97、 to introduce EDGE on the basis of GPRS network. Because adding EDGE function only needs upgrade of BSS, the network section can still use GPRS network for the entity. For BSS, the B~ of it only needs to upgrade software

98、 for radio resource management section; but the BTS need to upgrade partial hardware besides software upgrade. These upgrades are quite feasible either technically or from the viewpoint of engineering. The application ba

99、sis of EDGE is defined on</p><p>　　(4) IMT-2000</p><p>　　The ITU proposed Future Public Land Mobile Communications System (FPLMTS) in1985. In 1992 the World Administrative Radio Conference (WARC

100、) put its frequency on 2 000 MHz, and planned to enter commercial use around 2000. Under recommendation from some countries, the FPLMTS is formally renamed as IMT-2000 in 1996. It can realize that the user holding a set

101、can use it throughout the world. And wherever the user roam, he can get the same services, make the user not perceive the difference at all. Th</p><p>　　The major service feature of IMT-2000 is to support IP

102、 and high-speed data service. The access bandwidth of 2 Mbps for IMT-2000 allows it to provide true mobile multimedia service for the user. Meanwhile, because IMT-2000 supports asymmetric transmission of uplink and downl

103、ink for the service and supports transmitted data amount as reference for charge, it makes radio data service gain extensive application.</p><p>　　3. Development Trends of GSM Mobile Data Service</p>

104、<p>　　The development of radio mobile data service has a process to ensure smooth transition from 2G to 3G. The development trends of GSM mobile data service are shown in Figure 2. In the figure, from HSCSD to GPRS