Universal Mobile Telecommunications System (UMTS) nyaéta téknologi telepon sélulér generasi-katilu (3G).  Kiwari, bentuk UMTS anu pangilaharna, nu ngagunakeun W-CDMA salaku dadasar air interfacena, distandardisasi ku 3GPP, hiji forum standardisasi Éropah, pikeun nohonan standar IMT-2000 pikeun sistem radio sélulér 3G anu dikaluarkeun ku ITU.

Pikeun ngabédakeun UMTS ti téknologi jaringan sainganana, UMTS kadang dipasarkeun sabagé 3GSM, anu nyirikeun yén UMTS mangrupa gabungan tina sifat téknologi 3G jeung standar GSM.

Bubuka 
Artikel ieu medar téknologi, bisnis, kaguna katut aspék-aspék lianna ngeunaan UMTS, anu ngagunakeun air interface W-CDMA jeung  infrastruktur GSM.

Ciri/Kaistiméwaan 
UMTS, ku cara ngagunakeun W-CDMA, ngarojong laju transfer data sagancang 14,0 Mbit/s dina téori (lamun maké HSDPA), sanajan ayeuna para pamaké ieu teknologi bisa ngaharepkeun laju transfer nepi ka 384 kbit/s pikeun héndsét R99, sarta 3.6 Mbit/s pikeun héndsét HSDPA dina konéksi downlink. Laju transfer ieu masih jauh leuwih gancang manan hiji GSM error-corrected circuit switched data channel anu ngan 9,6 kbit/s atawa sababaraha channel anu ngan 9.6 kbit/s dina HSCSD (14.4 kbit/s pikeun CDMAOne). Laju transfer data ieu ogé leuwih gancang manan para pasaing téknologi jaringan lianna saperti CDMA2000, PHS atawa WLAN anu nawarkeun aksés ka World Wide Web dina alat télékomunikasi mobil.

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 théoretical 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 modérn coding schemes.  With EDGE the actual packet data rates can réach 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 7.2 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 vidéo calls is not very high.

Other possible uses for UMTS include the downloading of music and vidéo content, as well as live TV.

Deployment 
 See also: List of Deployed UMTS networks

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 éach 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 instéad, as the 1900 MHz band was alréady utilized. Additionally, in some countries UMTS operators use the 850 MHz and 1900 MHz bands (independently, méaning uplink and downlink are within the same band), notably in the US by AT&T Mobility. Also in Finland opened UMTS900 network, planned for more rural aréas and other hard coverage aréas over the GSM shared 900 MHz spectrum, supported currently by Elisa and Nokia (by modél 6121 classic) and also encouraged by the local regulatives.

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 béarer 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). Some software installs itself from the modem, so that in some cases 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 and UMTS data cards sold in Europe, the United States, much of Asia, and South Africa, are UMTS/GSM dual-mode devices, hence they are backwards compatible with regular GSM networks. If a UMTS customer travels to an aréa 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 méant 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 aréas 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 AT&T Mobility 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 AWS frequencies, but has been delayed by a lack of spectrum availability.  Because of the frequencies used, éarly modéls of UMTS phones designated for the US will likely not be operable overséas and vice versa; other standards, notably GSM, have faced similar problems, an issue déalt 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 alréady 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 yéars down the road - in any event they put some Européan telecom operators close to bankruptcy (most notably KPN). Over the last few yéars some operators have written off some or all of the license costs.

The UMTS spectrum allocated in Europe is alréady 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 Européan 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.

AT&T Mobility 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 gréater coverage compared to equivalent 1700/1900/2100Mhz networks, and is best suited to regional aréas where gréater 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 maké it éasier 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 éach 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 éasier, quicker, and considerably chéaper 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 countries, such as the United States and Japan, have allocated spectrum differently from the ITU Recommendations, so that the spectrum bands most commonly used for UMTS (UMTS-2100) have not been available.  In those countries, alternative bands are used, preventing the interoperability of existing UMTS-2100 equipment, and requiring the design and manufacture of different equipment for the use in these markets. As is the case with GSM today, this presumably will méan that standard UMTS equipment will not work in those markets, and some will work only in them, while some more-expensive equipment may be available that works in all markets. It also diminishes the economy of scale and benefit to users and network providers from the network effect that would have existed if these countries and the ITU had been able to agree on universally-applicable frequencies.

In the éarly days of UMTS there were issues with rollout:
 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;
 for fully fledged UMTS incorporating Video on Demand féatures, one base station needs to be set up every 1–1.5 km (0.62–0.93 mi). While this is economically féasible in urban aréas, it is inféasible in less populated suburban and rural aréas;
 in Ireland, Severe issues were encountered by users of 3G mobile broadband data modems on the rollout of their mobile broadband. It is not compatible with SMTP email programs and it is not possible to  “pop” your hotmail to Microsoft Outlook. It is also not possible to receive automatic Software Updates on Apple computers as the internet connection “times out”.

Some of these issues may still be ongoing; for instance, Apple, Inc. cited UMTS power consumption as the réason that the iPhone only supports EDGE.

See also 
 3G
 3GPP: the body that manages the UMTS standard.
 3GPP Long Term Evolution, the 3GPP project to evolve UMTS towards 4G capabilities.
 GAN/UMA: A standard for running GSM and UMTS over wireless LANs.
 Opportunity Driven Multiple Access, ODMA: a UMTS TDD mode communications relaying protocol
 HSDPA, HSUPA: updates to the W-CDMA air interface.
 PDCP
 Subscriber Identity Module
 UMTS-TDD: a variant of UMTS largely used to provide wireless Internet service.
 UMTS frequency bands
 W-CDMA: the primary air interface standard used by UMTS.
 W-CDMA 2100

Other, non-UMTS, 3G and 4G standards:
 CDMA2000: evolved from the cmdaOne (also known as IS-95, or "CDMA") standard, managed by the 3GPP2
 FOMA
 TD-SCDMA
 WiMAX: a newly emerging wide aréa wireless technology.

UMTS is an evolution of the GSM mobile phone standard.
 GSM
 GPRS
 EDGE
 ETSI

Other useful information
 Mobile modem
 Spectral efficiency comparison table
 Code Division Multiple Access (CDMA)
 Common pilot channel or CPICH, a simple synchronisation channel in WCDMA.
 Multiple-input multiple-output (MIMO) is the major issue of multiple antenna research.
 Wi-Fi: a local aréa wireless technology that is complementary to UMTS.
 Mobile Internet access worldwide lists mobile (mainly UMTS/HSDPA) Internet access solutions worldwide.
 List of device bandwidths

Literature 
 Martin Sauter: Communication Systems for the Mobile Information Society, John Wiley, September 2006, ISBN 0-470-02676-6

References

Tumbu luar 
 GSM/UMTS market statistics from the 'Global mobile suppliers association' 
 3GPP Specifications Numbering Scheme
 3GPP document listing all UMTS Technical Standards for Reléase 6 and éarlier 
 Vocabulary for 3GPP Specifications, up to Release 8
 UMTS FAQ on UMTS World d
 Worldwide W-CDMA frequency allocations on UMTS World
 UMTS TDD Alliance The Global UMTS TDD Alliance
 3GToday.com 
 3GSM World Congress

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