Universal Mobile Telecommunications System (UMTS) is one of the third-generation (3G) cell phone technologies. Currently, the most common form uses W-CDMA as the underlying air interface, is standardized by the 3GPP, and is the European answer to the ITU IMT-2000 requirements for 3G cellular radio systems. This system is mainly used in US whereas in Europe GSM system prevails. 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.

Features

UMTS, using W-CDMA, supports up to 14.0 Mbit/s data transfer rates in theory (with HSDPA), although at the moment users in deployed networks can expect a performance up to 384 kbit/s for R99 handsets, and 3.6 Mbit/s for HSDPA handsets in the downlink connection. This is still much greater than the 9.6 kbit/s of a single GSM error-corrected circuit switched data channel or multiple 9.6 kbit/s channels in HSCSD (14.4 kbit/s for CDMAOne), and—in competition to other network technologies such as CDMA2000, 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, IS-95, 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 140.8 kbit/s, though typical rates are closer to 56 kbit/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 more modern 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".

Since 2006, UMTS networks in many countries have been or are in the process of being upgraded with High Speed Downlink Packet Access (HSDPA), sometimes known as 3.5G. Currently, HSDPA enables downlink transfer speeds of up to 3.6 Mbit/s. Work is also progressing on improving the uplink transfer speed with the High-Speed Uplink Packet Access (HSUPA). Longer term, the 3GPP Long Term Evolution project plans to move UMTS to 4G speeds of 100 Mbit/s down and 50 Mbit/s up, using a next generation air interface technology based upon OFDM.

UMTS supports 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, as well as live TV.

Deployment

See also: List of Deployed UMTS networks (not updated)

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, TD-CDMA, or TD-SCDMA air interfaces, GSM's Mobile Application Part (MAP) core, and the GSM family of speech codecs. In the most popular cellular mobile telephone variant of UMTS, W-CDMA is currently used. Note that other wireless standards use W-CDMA as their air interface, including FOMA.

UMTS over W-CDMA uses a pair of 5 MHz channels. 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 acted relatively slowly in allocating new frequencies specifically for 3G services (such as the United States).

The specific frequency bands originally defined by the UMTS standard are 1885-2025 MHz for the mobile-to-base (uplink) and 2110-2200 MHz for the base-to-mobile (downlink). In the US, 1710-1755 MHz and 2110-2155 MHz will be used instead, as the 1900 MHz band was already utlized.[1] Additionally, in some countries UMTS operators use the 850 MHz and 1900 MHz bands (independently, meaning uplink and downlink are within the same band), notably in the US by AT&T Mobility.

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 (GeRAN). It can be connected to various backbone networks like the Internet, ISDN, GSM or to a UMTS network. GeRAN 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.

3G external modems

Using a cellular router, PCMCIA or USB card, customers are able to access 3G broadband services, regardless of their choice of computer (such as a tablet PC or a PDA). Even the software installs itself from the modem, so that absolutely no knowledge of technology is required to get online in moments.

Using a phone that supports 3G and Bluetooth 2.0, multiple Bluetooth-capable laptops can be connected to the Internet. The phone acts as a router, but via Bluetooth rather than wireless networking(802.11) or a USB connection.

Interoperability and global roaming

At the air interface level, UMTS itself is incompatible with GSM. UMTS phones sold in Europe/Hong Kong(as of 2007) 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.

Softbank (formerly Vodafone Japan, formerly J-Phone) operates a 3G network based on UMTS compatible W-CDMA technology, that launched in December 2002. Lack of investment in the network through 2003 meant that coverage was slow to expand and subscriber numbers remained low. The network was publicly relaunched in October 2004 and again in 2005, and Vodafone now claims network coverage of 99% of the population, while 15% of their subscribers are 3G users.

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 is currently offered by Cingular on 850 MHz and 1900 MHz, due to the limitations of the spectrum available to them at the time they launched UMTS service. T-Mobile will be rolling out UMTS on the 2100/1700 MHz frequencies in mid 2007. Because of the frequencies used, early models of UMTS phones designated for the US will likely not be operable overseas and vice versa; other standards, notably GSM, have faced similar problems, an issue dealt with by the adoption of multi-band phones. Most UMTS licensees seem to consider ubiquitous, transparent global roaming an important issue.

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. In Europe, the license process occurred at the end of the technology bubble, and the auction mechanisms for allocation set up in some countries resulted in some extremely high prices being paid, notable in the UK and Germany. In Germany, bidders paid a total 50.8 billion euros for six licenses, two of which were subsequently abandoned and written off by their purchasers (Mobilcom and the Sonera/Telefonica consortium). It has been suggested that these huge license fees have the character of a very large tax paid on income expected 10 years down the road - in any event they put some European telecom operators close to bankruptcy (most notably KPN). Over the last few years some operators have written off some or all of the license costs.

The UMTS spectrum allocated in Europe 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 have however, freed up some of the 2100 MHz range for 3G services, together with the 1700 MHz for the uplink. UMTS operators in North America who want to implement a European style 2100/1900 MHz system will 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.

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. T-Mobile's roll-out of UMTS in the US will focus on the 2100/1700 MHz bands just auctioned.

Cingular Wireless is rolling out some cities with a UMTS network at 850 MHz to enhance its existing UMTS network at 1900 MHz and now offers subscribers a number of UMTS 850/1900 phones. In Australia, Telstra rolled out the NextG network, a 3G UMTS network operating in the 850 MHz band to replace the existing CDMA network (February 2008) and enhance its existing 2100 MHz UMTS network. The 850 MHz band provides greater coverage compared to equivalent 1700/1900/2100Mhz networks, and is best suited to regional areas where greater distances separate subscriber and base station.

Other competing standards

There are other competing 3G standards, such as FOMA, CDMA2000 and TD-SCDMA, though UMTS can use the latter's air interface standard. FOMA and UMTS similarly share the W-CDMA air interface system.

On the Internet access side, competing systems include WiMAX and Flash-OFDM. Different variants of UMTS compete with different standards. While this article has largely discussed UMTS-FDD, a form oriented for use in conventional cellular-type spectrum, UMTS-TDD, a system based upon a TD-CDMA air interface, is used to provide UMTS service where the uplink and downlink share the same spectrum, and is very efficient at providing asymmetric access. It provides more direct competition with WiMAX and similar Internet-access oriented systems than conventional UMTS.

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

CDMA2000's narrower bandwidth requirements make it easier than UMTS to deploy in existing spectrum along with legacy standards. In some, but not all, cases, existing GSM operators only have enough spectrum to implement either UMTS or GSM, not both. For example, in the US D, E, and F PCS spectrum blocks, the amount of spectrum available is 5 MHz in each direction. A standard UMTS system would saturate that spectrum.

In many markets however, the co-existence issue is of little relevance, as legislative hurdles exist to co-deploying two standards in the same licensed slice of spectrum.

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, AT&T 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. Bitė Lietuva (Lithuania) was one of the first operators in Europe to launch EDGE in December 2003. 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

In the early days of UMTS there were issues with rollout and continuing development:-

• 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 - in most networks around the world this is no longer an issue;
• 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 (0.62–0.93 mi). While this is economically feasible in urban areas, it is infeasible in less populated suburban and rural areas;
• Some countries, such as the United States, have allocated spectrum that differs from what had been almost universally agreed, preventing the use of existing UMTS-2100 equipment, and requiring the design and manufacture of different equipment for use in these markets. As is the case with GSM today, this presumably will mean that some UMTS equipment will work only in some markets, and some will work only in others, and some more-expensive equipment may be available that works in all markets. It also diminishes the economy of scale and benefit to users from the network effect that would have existed if these few countries had harmonized their regulations with the others.