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UMTS(英)

2006-02-21 00:00wikipedia

Universal Mobile Telecommunications System (UMTS) is one of the third-generation (3G) mobile phone technologies. It uses W-CDMA as the underlying standard, is standardized by the 3GPP, and represents the European/Japanese answer to the ITU IMT-2000 requirements for 3G Cellular radio systems.

To differentiate UMTS from competing network technologies, UMTS is sometimes marketed as 3GSM, emphasizing the combination of the 3G nature of the technology and the GSM standard which it was designed to succeed.

Preface

This article discusses the technology, business, usage and other aspects encompassing and surrounding UMTS, the 3G successor to GSM which utilizes the W-CDMA air interface and GSM infrastructures. Any issues relating strictly to the W-CDMA interface itself may be better described in the W-CDMA page.

Due to the rapid nature of UMTS development in the market place, some information on this page may become quickly outdated. Readers' discretion and additional independent research is strongly advised; you are encouraged to return and add updates to this page. Contributors are also advised to timestamp their contributions when appropriate in order to help readers to determine the age of the information.
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Features

UMTS supports up to 1920 kbit/s data transfer rates (and not 2 Mbit/s as frequently seen), although at the moment users in the real networks can expect performance up to 384 kbit/s - in Japan upgrades to 3 Mbit/s are in preparation. However, this is still much greater than the 14.4 kbit/s of a single GSM error-corrected circuit switched data channel or multiple 14.4 kbit/s channels in HSCSD, and - in competition to other network technologies such as CDMA-2000, PHS or wLAN - offers access to the World Wide Web and other data services on mobile devices.

Precursors to 3G are 2G mobile telephony systems, such as GSM, CDMA, PDC, PHS and other 2G technologies deployed in different countries. In the case of GSM, there is an evolution path from 2G, called GPRS, also known as 2.5G. GPRS supports a much better data rate (up to a theoretical maximum of 140.8kbit/s, though typical rates are closer to 56kbit/s) and is packet switched rather than connection oriented (circuit switched). It is deployed in many places where GSM is used. E-GPRS, or EDGE, is a further evolution of GPRS and is based on new "coding schemes". With EDGE the actual packet data rates can reach around 180 kbit/s (effective). EDGE systems are often referred as "2.75G Systems".

In 2006, UMTS networks in Japan will be upgraded with High Speed Downlink Packet Access (HSDPA), sometimes known as 3.5G. This will make a downlink transfer speed of up to 14.4 Mbit/s possible. Work is also progressing on improving the uplink transfer speed with the High-Speed Uplink Packet Access (HSUPA)

In 2006, Vodacom in South Africa is also working towards implementing High Speed Downlink Packet Access (HSDPA).

In Austria, Mobilkom Austria already implemented and deployed HSDPA for public usage.

Marketing material for UMTS has emphasised the possibility of mobile videoconferencing, although experience in Japan and elsewhere has shown that user demand for Video calls is not very high.

Other possible uses for UMTS include the downloading of music and video content.

Real-world implementations

The first large scale real-life commercial UMTS network in the world went live in 2001 in Japan, operated by NTT DoCoMo.

In December 2003, T-Mobile launched UMTS in Austria, and began trials in the UK and Germany. Also, in November 2005 the T-Mobile UMTS network in the Netherlands went live (however, this was not a commercial launch, but meant to meet regulatory requirements imposed upon the spectrum auction).

In February 2004, Vodafone began a wide-scale UMTS launch in several European markets, including the UK, Germany, The Netherlands and Sweden. In Portugal, UMTS was launched just before the Euro 2004 began.

The first UMTS network in Poland was launched in 2004 by Plus GSM, but coverage was still limited to Warsaw. In April 2005, Era GSM launched another UMTS network in Warsaw, providing cheap (about 20 euros per month) internet access, among other 3G services. In January 2006 most of top major cities are covered by Era GSM, Orange and Plus GSM.

In the Czech Republic, UMTS was launched by T-Mobile in 2005.

The first UMTS network in Africa was launched on the island of Mauritius in November 2004, followed by Vodacom's launch of 3G services in South Africa in December 2004.

In Finland, UMTS licenses were provided by the government free of charge. In 2004, Elisa Oyj and TeliaSonera began deploying commercial UMTS networks, and in 2005 Dna Finland began commercial UMTS service.

Under a previous agreement with NTT DoCoMo, US provider AT&T Wireless (now Cingular) was required to build and market UMTS networks in four major United States cities by the end of 2004. At CTIA 2004, Cingular announced that their 3G network would be a 1900-only implementation of UMTS and would launch by the end of that year as planned. As of January 2006, Cingular has deployed UMTS networks in Dallas, Detroit, Phoenix, San Diego, San Francisco, and Seattle.

Because the US has not yet provided new spectrum for UMTS, it must share the 850MHz and 1900MHz bands allocated for cellular communication in the US with existing 1G and 2G networks. The UMTS requirement for 5 MHz frequency slots, much larger than that required for existing networks, can create difficulty for US operators.

In Singapore, Singapore Telecommunications started their trial during December 2004 and it was successfully launched during March 2005 followed by StarHub and MobileOne.

Operators are starting to sell mobile internet products that combine 3G and Wi-Fi in one service. Laptop owners are sold a UMTS modem and given a client program that detects the presence of a Wi-Fi network and switches between 3G and Wi-Fi when available. Initially Wi-Fi was seen as a competitor to 3G, but it is now recognised that as long as the operator owns or leases the Wi-Fi network, they will be able to offer a more competitive product than with UMTS only. Nokia has forecasted that UMTS devices will make one sixth of all cellular phones by the end of 2006.

Technology

The following information does not apply to non-UMTS systems that use the W-CDMA air interface, such as FOMA

UMTS combines the W-CDMA air interface, GSM's Mobile Application Part (MAP) core, and the GSM family of speech codecs.

Note that many wireless technologies use W-CDMA as their air interface, including FOMA and J-Phone.

Like other real-world W-CDMA implementations, UMTS uses a pair of 5 MHz channels, one in the 1900 MHz range for uplink and one in the 2100 MHz range for downlink. In contrast, the competing CDMA2000 system uses one or more arbitrary 1.25 MHz channels for each direction of communication. UMTS and other W-CDMA systems are widely criticized for their large spectrum usage, which has delayed deployment in countries that have not allocated new frequencies specifically for UMTS (such as the United States).

The specific frequency bands originally defined by the UMTS standard are 1885-2025 MHz for uplink and 2110-2200 MHz for downlink.

For existing GSM operators, it is a simple but costly migration path to UMTS: much of the infrastructure is shared with GSM, but the cost of obtaining new spectrum licenses and overlaying UMTS at existing towers can be prohibitively expensive.

A major difference of UMTS compared to GSM is the air interface forming Generic Radio Access Network (GRAN). It can be connected to various backbone networks like the Internet, ISDN, GSM or to a UMTS network. GRAN includes the three lowest layers of OSI model. The network layer (OSI 3) protocols form the Radio Resource Management protocol (RRM). They manage the bearer channels between the mobile terminals and the fixed network including the handovers.

Interoperatibility and global roaming

At the air interface level, UMTS itself is incompatible with GSM. UMTS phones sold in Europe (as of 2004) are UMTS/GSM dual-mode phones, hence they can also make and receive calls on regular GSM networks. If a UMTS customer travels to an area without UMTS coverage, a UMTS phone will automatically switch to GSM (roaming charges may apply). If the customer travels outside of UMTS coverage during a call, the call will be transparently handed off to available GSM coverage.

Regular GSM phones cannot be used on the UMTS networks.

Vodafone Japan (former J-Phone) has a 3G network which uses W-CDMA technology and is compatible with UMTS. However, when Vodafone acquired J-Phone, Vodafone dramatically reduced the investments planned in UMTS infrastructure, so that, subscriber numbers of Vodafone Japan's UMTS network used to remain low, and 3G coverage of Japan was once incomplete. Now Vodafone Japan claims that more than 99% of the populated area is covered by 3G network, and 15% of its subscribers are 3G users as of the end of 2005.

NTT DoCoMo's 3G network, FOMA, was the first commercial network using W-CDMA since 2002. The first W-CDMA version used by NTT DoCoMo was incompatible with the UMTS standard at the radio level, however USIM cards used by FOMA phones are compatible with GSM phones, so that USIM card based roaming is possible from Japan to GSM areas without any problem. Today the NTT DoCoMo network - as well as all the W-CDMA networks in the world - use the standard version of UMTS, allowing potential global roaming. Whether and under which conditions roaming can actually be used by subscribers depends on the commercial agreements between operators.

All UMTS/GSM dual-mode phones should accept existing GSM SIM cards. Sometimes, you are allowed to roam on UMTS networks using GSM SIM cards from the same provider.

In the United States, UMTS will initially be offered (by Cingular, formerly AT&T Wireless) on the 1900 MHz spectrum only, due to existing limitation of spectrum allocated in the United States. UMTS phones designated for the US will likely not be operable overseas and vice versa; this mirrors the current situation of GSM phones and GSM networks in the US using different frequencies from those used in the rest of the world. However, the FCC has made reasonable promises to free up additional spectrum in the 2100 MHz band and most UMTS licensees seem to consider ubiquituous, transparent global roaming an important issue.

Although roaming is possible between compatible European and Asian networks, there is still no roaming possible with the United States (as of December 2004).

Spectrum allocation

Over 120 licenses have already been awarded to operators worldwide (as of December 2004), specifying W-CDMA radio access technology that builds on GSM. With the technology still emerging, politicians hurriedly set up license auctions, which funneled billions of dollars in license fees into public budgets. In Germany alone, license holders paid a total 50.8 billion euros. Operators are expected to begin gaining income from those licenses in 2005. These huge license fees have the character of a very large tax paid on income expected 10 years down the road, created huge losses, and put many European telecom operators close to bankruptcy. Over the last few years these losses have been written off, and the associated debt has been reduced, largely through income from SMS data services.

The UMTS spectrum allocated by ITU is already used in North America. The 1900 MHz range is used for 2G (PCS) services, and 2100 MHz range is used for satellite communications. Regulators are trying to free up the 2100 MHz range for 3G services, though UMTS in North America will still have to share spectrum with existing 2G services in the 1900 MHz band. 2G GSM services elsewhere use 900 MHz and 1800 MHz and therefore do not share any spectrum with planned UMTS services.

Until regulators allocate new spectrum specifically for 3G, there will be no firm answer to what frequencies UMTS will operate on in North America. AT&T Wireless launched UMTS services in the United States by the end of 2004 strictly using the existing 1900 MHz spectrum allocated for 2G PCS services. Cingular acquired AT&T Wireless in 2004 and has since then launched UMTS in select US cities. Initial rollout of UMTS in Canada will also be handled exclusively by the 1900 MHz band.

Other competing standards

There are other competing 3G standards, such as CDMA2000 and systems including iBurst from Arraycom, Flarion and wCDMA-TDD (IPWireless).

Both CDMA2000 and W-CDMA are accepted by ITU as part of the IMT-2000 family of 3G standards, in addition to Enhanced Data Rates for Global Evolution (EDGE) and China's own 3G standard, TD-SCDMA.

CDMA2000, being an evolutionary upgrade to cdmaOne, does not require new spectrum allocation and will operate comfortably in existing PCS spectrums.

Most GSM operators in North America as well as others around the world have accepted EDGE as a temporary 3G solution. AT&T Wireless launched EDGE nationwide in 2003, Cingular launched EDGE in most markets and T-Mobile USA has launched EDGE nationwide as of October 2005. Rogers Wireless launched nation-wide EDGE service in late 2003 for the Canadian market. TIM (Italy) launched EDGE in 2004. The benefit of EDGE is that it leverages existing GSM spectrums and is compatible with existing GSM handsets. It is also much easier, quicker, and considerably cheaper for wireless carriers to "bolt-on" EDGE functionality by upgrading their existing GSM transmission hardware to support EDGE than having to install almost all brand-new equipment to deliver UMTS. EDGE provides a short-term upgrade path for GSM operators and directly competes with CDMA2000.

Problems and issues

Some of the rollout problems operators faced included:

  • overweight handsets with poor battery life;
  • problems with handover from UMTS to GSM, connections being dropped or handovers only possible in one direction (UMTS->GSM) with the handset only changing back to UMTS after hanging up, even if UMTS coverage returns;
  • initially poor coverage due to the time it takes to build a network;
  • for fully fledged UMTS incorporating Video on Demand features, one base station needs to be set up every 1–1.5 km. While this is economically feasible in urban areas, it is impossible in less populated suburban and rural areas;
  • competition for broadband access from Wi-Fi;
  • lack of significant consumer demand for 3G.

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