For effective, efficient communications, standardization is critical, and nowhere is this more evident than in the areas of mobile computing and cellular telephony.
If you need data access or e-mail through your cell phone, you’re likely to be using one of two different technologies: Code Division Multiple Access (CDMA) or Global Service of Mobile Communication (GSM).
Both CDMA and GSM are second-generation (2G) technologies, and they have co-existed for several years. Each technology has its supporters. CDMA phones are engineered specifically for an individual carrier, whereas GSM phones make use of a removable memory card called the Subscriber Identity Module (SIM). A SIM card contains all the key information required to activate a phone, including the user’s telephone number, personal identification number, address book and encoded network identification details. A user can easily move a SIM from one phone to another.
Though GSM phones are interoperable with one another, different countries use different parts of the frequency spectrum, so “world phones” typically must be capable of using several frequencies.
Today, the fastest-growing use of cellular networks is for the transmission of all kinds of data and rich media, including Web sites, video, music, images, and maps and driving directions. The older 2G networks simply couldn’t handle that volume of traffic, and they couldn’t offer the speed needed for transmitting large files. The answer was to make the services faster and build out the networks to deal with more traffic.
Here, too, the CDMA and GSM paths continued their separate but parallel development. CDMA brought us CDMA2000 and 1xRTT networks. The most recent developments are 1x Evolution Data Optimized, or EV-DO, and 1x Evolution Data/Voice, or EV-DV.
Similarly, GSM begat General Packet Radio Service, or GPRS, which begat enhanced data rates for GSM evolution, or EDGE. EDGE was developed to enable the transmission of large amounts of data at a high speed, 384Kbit/sec. The latest generation is called Wideband Code Division Multiple Access (WCDMA).
And this finally brings us to Universal Mobile Telecommunications System.
The International Telecommunication Union (ITU), a specialized agency of the United Nations, has attempted to coordinate these competing technologies to improve throughput and increase interoperability. The International Mobile Telecommunications 2000 standard is a third-generation digital communications specification from the ITU. And the European (i.e., GSM-based) implementation of IMT-2000 is UMTS, which is based on WCDMA. Previous cellular telephone data systems were mostly circuit-switched, requiring a dedicated connection. WCDMA is packet-switched, using the Internet Protocol. The first commercial WCDMA network was launched in Japan in 2001.
UMTS has been specified as an integrated application for mobile voice and data systems with wide-area coverage. aUsing globally harmonized spectrum in paired and unpaired bands, early implementations of UMTS offer theoretical bit rates of up to 384Kbit/sec. in situations where the mobile device is actually moving. The current goal is to achieve 2Mbit/sec. when both ends of the connection are (at least temporarily) stationary.
UMTS operates on radio frequencies identified by the ITU IMT-2000 specification document and licensed to operators, using a 5-MHz-wide channel that simplifies deployment for network providers that have been granted large, contiguous blocks of spectrum. Most UMTS systems use frequencies between 1,885 and 2,025 MHz.
UMTS assigns separate carrier frequencies to incoming and outbound signals, a process called frequency division duplexing (FDD). For symmetric traffic, such as two-way videophones, FDD is highly efficient, allowing uplink and download data rates to be equal, in contrast to technologies such as Asymmetric Digital Subscriber Line service, which typically offers upload rates that are much slower than its download rates. FDD reduces interference and wastes no bandwidth in switching from transmitting to receiving.
Ongoing work within the 3rd Generation Partnership Project promises increased throughput speeds over the WCDMA Radio Access Network. High-Speed Downlink Packet Access and High-Speed Uplink Packet Access technologies are already standardized, and commercial operators in Asia and North America are putting them through network trials. With theoretical download speeds as high as 14.4Mbit/sec. and uplink speeds of up to 5.8Mbit/sec., these technologies will make it possible for UMTS to offer data transmission speeds comparable to those of hard-wired Ethernet-based networks.
通用移動通信系統（UMTS）
為了有效地進行高效的通信，標準化是至關重要的，在移動計算和蜂窩網電話領域中這一點更為明顯。
如果你需要通過手機訪問數據或收發電子郵件，那么你就要使用下列兩種不同技術中的一種：碼分多址（CDMA）或全球通（GSM）。
CDMA和GSM都是第二代技術（2G），它們已共存多年,每種技術都有支持者。CDMA手機電話是專為一家營運商設計的，而GSM手機電話使用了可抽取的存儲卡，叫做用戶身份識別模塊（SIM卡）。SIM卡包含了打電話所需的所有關鍵信息，如用戶的電話號碼、個人身份識別號碼、地址簿以及編了碼的網絡識別細節等。用戶很容易將SIM卡從一部電話插入另一部電話。
雖然GSM電話相互間能互操作，但不同的國家使用不同的頻段，所以典型的“世界電話”必須能使用多個頻率。
今天，蜂窩網發展最快的用途是傳送各種各樣的數據和富媒體，包括網站、視頻、音樂、以及地圖與駕車指示等。較陳舊的2G網絡不能處理這么大的流量，它們也不能提供傳送大文件所需的速度。解決辦法就是使這些服務的速度更快和構建能處理更大流量的網絡。
對此，CDMA和GSM各自繼續向前發展。CDMA帶給我們的是CDMA2000和1xRTT網。最新的進展是EV-DO（1x演進數據優化）和EV-DV（1x演進數據/話音）。
同樣，GSM也產生了GPRS（通用包無線電業務），為GSM的演進提高了數據速率，即EDGE。開發EDGE是為了能在384Kb/秒的速度下實現傳送大容量的數據。最新的一代叫寬帶碼分多址（WCDMA）。
最后，給我們帶來了通用移動通信系統（UMTS）。
國際電信聯盟（ITU）是聯合國下屬的一個專門機構，它試圖協調這些相競爭的技術，以提高吞吐量和增強互操作性。國際移動通信2000（IMT-2000）是ITU的第三代數字通信規范。IMT2000的歐洲（基于GSM的）實現就是UMTS，它基于WCDMA。以前的蜂窩網電話數據系統多數是電路交換的，需要專門的連接。而WCDMA是包交換的，采用因特網協議。第一個商用WCDMA于2001年在日本開通�！ � UMTS已經被指定為大范圍覆蓋的移動話音和數據系統的綜合應用。利用全球協調的成對和不成對頻段，早期的UMTS實現了對實際移動著的移動設備提供384Kb/秒的理論速率。當前的目標是當連接的兩端是固定時（至少暫時）要達到2Mb/秒。
UMTS工作在ITU IMT-2000規范文檔指定并發放給營運商的無線電頻率上，使用5兆赫頻寬的信道簡化了那些被授予連續的大頻段的網絡提供商的部署。大多數UMTS系統使用1885 至2025 兆赫之間的頻率。
UMTS分配給營運商不同的頻率，用于輸入和輸出信號，這個過程叫頻分雙工（FDD）。對于對稱流量，如雙向視頻會議，FDD非常高效，使上行鏈和下載的速率相等，剛好與非對稱數據用戶線（ADSL）技術相反，后者通常提供的上載速度遠遠低于下載速度。FDD也減少了從發射轉換到接收時的干擾和帶寬浪費。
第三代合作伙伴計劃中正在進行的工作，有望在WCDMA無線電接入網上提高吞吐速度。高速下行鏈包接入和高速上行鏈包接入已經實現了標準化，亞洲和北美的商業營運商正在網絡試驗中采用。理論的下載速度可達14.4Mb/秒、上行鏈速度達5.8Mb/秒，這些技術將使UMTS能夠提供與硬布線以太網相比擬的數據傳輸速度。
文章來源于領測軟件測試網 http://www.kjueaiud.com/
