Universal Mobile Telecommunications System
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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.
Contents |
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Due to the rapid nature of UMTS development in the market place, some information on this page may become quickly outdated.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.
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).
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 (wCDMA) network in the world went live in 2001 in Japan operated by DoCoMo.
3 is an upstart 3G network primarily owned by Hutchison Whampoa and its partners. Its partners vary depending on the country. It soon launched other UMTS networks worldwide that to-date (December 2004) include Australia, Austria, Denmark, Hong Kong, Israel, Italy, Portugal, Republic of Ireland, Sweden and the United Kingdom. Most major western European GSM operators plan to upgrade to UMTS in the future, since it is closely allied with the GSM 2G standard.
In December 2003, T-Mobile launched UMTS in Austria, with trials in the UK and Germany.
In February 2004, Vodafone had a wide-scale UMTS launch in several European markets, including, UK, Germany, Netherlands and Sweden. In Portugal, UMTS was launched just before the Euro 2004 begun.
The first UMTS network in Poland was launched in 2004 by Plus GSM, but the coverage is 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.
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.
Under a previous agreement with NTT DoCoMo, American AMPS/TDMA/GSM provider AT&T Wireless was required to build and market UMTS networks in four major United States cities by the end of 2004. At CTIA 2004, AT&T Wireless 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 July 2004, AT&T Wireless (now part of Cingular) has successfully launched UMTS service in Seattle (Washington), San Francisco (California), Detroit (Michigan), Phoenix (Arizona), San Diego (California) and Dallas (Texas).
Since merging with AT&T Wireless, Cingular has announced plans to begin deployment of UMTS along with HSDPA in 2005. Unlike the initial AT&T deployment of UMTS, Cingular's expanded (and eventually, nationwide) deployment of UMTS will run on both of their existing 1900 MHz and 850 MHz frequencies.
T-Mobile USA has stated they have no plans to deploy UMTS until 2007.
Because the US has not provided new spectrum for UMTS, it must share spectrum with the existing 1G and 2G systems. 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.
See #External links for a list of UMTS networks (live and under testing).
Technology
Note: Most of the underlying technological aspects of UMTS are common among all W-CDMA variants. Please see W-CDMA for more info. The followings are some technical information specific to UMTS, not shared by FOMA or other W-CDMA implementations.
Simply put, UMTS is the combination of the W-CDMA air interface (the protocol that defines over-the-air transmissions between UMTS mobile phones and towers), GSM's Mobile Application Part (MAP) core (the protocol that provides mobile functionality like to route calls to and from mobile subscriber), and the GSM family of speech codecs like AMR and EFR (the protocols which define how audio is digitized, compressed and encoded). Technically speaking, W-CDMA (as per the definition of IMT2000) is merely the air interface, while UMTS is the complete stack of communication protocols designated for 3G global mobile telecommunications and as a direct successor to GSM. However, W-CDMA is frequently used as a general, umbrella term to collectively refer to the family of 3G standards that uses W-CDMA as its air interface, that includes UMTS, 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, CDMA2000 uses one or more arbitrary 1.25 MHz channels of each direction of transmissions. UMTS is frequently criticized for its heavy bandwidth requirements.
The specific frequency bands originally defined by the UMTS standard are 1885-2025 MHz for uplink and 2110-2200 MHz for downlink. See #External links at the bottom of this page for a map of UMTS frequency allocation.
For existing GSM operators, it is a simple but costly migration path to UMTS: most of the rest of their infrastructures may remain the same, 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 as of this date, subscriber numbers of Vodafone Japan's UMTS network is still very low, and coverage of Japan is incomplete.
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 has committed to provide UMTS services in the United States by the end of 2004 strictly using the existing 1900 MHz spectrum allocated for 2G PCS services. 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 existing GSM operators take a wait-and-see approach to UMTS, due to the high cost of obtaining new frequency spectrums and equipment.
Most GSM operators in North America have accepted EDGE as a temporary 3G solution. AT&T Wireless launched EDGE nationwide in 2003, Cingular launched EDGE in limited markets and T-Mobile USA plans to provide EDGE nationwide. 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. 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.
See also
- W-CDMA: the technology on which UMTS is based
- CDMA2000: a competing 3G standard evolved from the CDMA standard (aka IS-95 or cdmaOne)
- Wi-Fi: a local area wireless technology that is complementary to UMTS, but undermines many of the early UMTS business models
- WiMAX: a newly emerging wide area wireless technology. Will be discussed in detail at a later stage.
- IMS IP Multimedia Subsystem
- PN Sequences
External links
- UMTS FAQ on UMTS World d
- Worldwide W-CDMA frequency allocations on UMTS World
- Worldwide UMTS Deployment on UMTS Forum
- 3G Japan FAQ
- UMTS TDD Alliance The Global UMTS TDD Alliance
- 3GToday.com
- Radio-Electronics.Com Free UMTS / WCDMA tutorial
