Editing UMTS (section)

== Air interfaces ==
[[File:UMTS structures.svg|thumb|400px|UMTS network architecture]]
[[File:UMTS.jpg|thumb|300px|UMTS network architecture]]
UMTS combines three different terrestrial [[air interface]]s, [[Global System for Mobile Communications|GSM]]'s [[Mobile Application Part]] (MAP) core, and the GSM family of [[speech codec]]s.

The air interfaces are called UMTS Terrestrial Radio Access (UTRA).<ref name="glossary01">{{cite web |url=http://www.3gnewsroom.com/html/glossary/u.shtml |title=3G Glossary{{Snd}} UTRA | website=3GNewsroom.com |date=2003-11-29 |archive-url=https://web.archive.org/web/20110406074310/http://www.3gnewsroom.com/html/glossary/u.shtml |archive-date=2011-04-06}}</ref> All air interface options are part of [[ITU]]'s [[IMT-2000]]. In the currently most popular variant for cellular mobile telephones, W-CDMA (IMT Direct Spread) is used. It is also called "Uu interface", as it links User Equipment to the UMTS Terrestrial Radio Access Network.

Please note that the terms [[W-CDMA]], [[TD-CDMA]] and [[TD-SCDMA]] are misleading. While they suggest covering just a [[channel access method]] (namely a variant of [[CDMA]]), they are actually the common names for the whole air interface standards.<ref name="ituover">{{cite web|url=http://www.itu.int/dms_pub/itu-d/opb/stg/D-STG-SG02.18-1-2006-PDF-E.pdf|author=ITU-D Study Group 2|title=Guidelines on the smooth transition of existing mobile networks to IMT-2000 for developing countries (GST); Report on Question 18/2|access-date=2009-06-15|pages=4, 25–28}}</ref>

=== W-CDMA (UTRA-FDD) ===
W-CDMA (WCDMA; Wideband [[Code-Division Multiple Access]]), along with UMTS-FDD, UTRA-FDD, or IMT-2000 CDMA Direct Spread is an air interface standard found in [[3G]] [[mobile telecommunications]] networks. It supports conventional cellular voice, text and [[Multimedia Messaging Service|MMS]] services, but can also carry data at high speeds, allowing mobile operators to deliver higher bandwidth applications including streaming and broadband Internet access.<ref>{{cite web|url=http://www.gsma.com/aboutus/gsm-technology/3gwcdma |title=What is 3G/WCDMA? |work=About Us |publisher=GSMA.com |access-date=2014-06-24 |url-status=dead |archive-url=https://web.archive.org/web/20140625040221/http://www.gsma.com/aboutus/gsm-technology/3gwcdma |archive-date=2014-06-25}}</ref>

W-CDMA uses the [[DS-CDMA]] channel access method with a pair of 5&nbsp;MHz wide channels. In contrast, the competing [[CDMA2000]] system uses one or more available 1.25&nbsp;MHz channels for each direction of communication. W-CDMA systems are widely criticized for their large spectrum usage, which delayed deployment in countries that acted relatively slowly in allocating new frequencies specifically for 3G services (such as the United States).

The specific [[Band (radio)|frequency bands]] originally defined by the UMTS standard are 1885–2025&nbsp;MHz for the mobile-to-base (uplink) and 2110–2200&nbsp;MHz for the base-to-mobile (downlink). In the US, 1710–1755&nbsp;MHz and 2110–2155&nbsp;MHz are used instead, as the 1900&nbsp;MHz band was already used.<ref>{{cite web |website=[[Federal Communications Commission]] |url=http://wireless.fcc.gov/services/aws/data/awsbandplan.pdf |title=Advanced Wireless Services (AWS) Band Plan |archive-url=https://web.archive.org/web/20100705121710/http://wireless.fcc.gov/services/aws/data/awsbandplan.pdf |archive-date=2010-07-05 |url-status=dead}}</ref> While UMTS2100 is the most widely deployed UMTS band, some countries' UMTS operators use the 850&nbsp;MHz (900&nbsp;MHz in Europe) and/or 1900&nbsp;MHz bands (independently, meaning uplink and downlink are within the same band), notably in the US by [[AT&T Mobility]], New Zealand by [[Telecom New Zealand]] on the [[XT Mobile Network]] and in Australia by [[Telstra]] on the [[Next G]] network. Some carriers such as [[T-Mobile US|T-Mobile]] use band numbers to identify the UMTS frequencies. For example, Band I (2100&nbsp;MHz), Band IV (1700/2100&nbsp;MHz), and Band V (850&nbsp;MHz).

UMTS-FDD is an acronym for Universal Mobile Telecommunications System (UMTS){{Snd}} [[frequency-division duplex]]ing (FDD) and a [[3GPP]] [[standardized]] version of UMTS networks that makes use of frequency-division duplexing for [[duplex (telecommunications)|duplex]]ing over an UMTS Terrestrial Radio Access ([[UTRA]]) air interface.<ref name="ts25.201">{{cite web |url=http://www.3gpp.org/DynaReport/25201.htm |title=TS 25.201 |access-date=2009-02-23 |author=3GPP}}</ref>

W-CDMA is the basis of Japan's [[NTT DoCoMo]]'s [[Freedom of Mobile Multimedia Access|FOMA]] service and the most-commonly used member of the Universal Mobile Telecommunications System (UMTS) family and sometimes used as a synonym for UMTS.<ref>3GPP notes that "there currently existed many different names for the same system (eg FOMA, W-CDMA, UMTS, etc)"; {{cite web|title=Draft summary minutes, decisions and actions from 3GPP Organizational Partners Meeting#6, Tokyo, 9 October 2001|author=[[3GPP]]|url=http://www.3gpp.org/ftp/op/OP_07/DOCS/pdf/OP6_13r1.pdf|pages=7}}</ref> It uses the DS-CDMA channel access method and the FDD duplexing method to achieve higher speeds and support more users compared to most previously used [[time-division multiple access]] (TDMA) and [[time-division duplex]] (TDD) schemes.

While not an evolutionary upgrade on the airside, it uses the same [[core network]] as the [[2G]] GSM networks deployed worldwide, allowing [[dual-mode mobile]] operation along with GSM/[[Enhanced Data Rates for GSM Evolution|EDGE]]; a feature it shares with other members of the UMTS family.

==== Development ====
In the late 1990s, W-CDMA was developed by NTT DoCoMo as the air interface for their 3G network [[FOMA]]. Later NTT DoCoMo submitted the specification to the [[International Telecommunication Union]] (ITU) as a candidate for the international 3G standard known as IMT-2000. The ITU eventually accepted W-CDMA as part of the IMT-2000 family of 3G standards, as an alternative to CDMA2000, EDGE, and the short range [[DECT]] system. Later, W-CDMA was selected as an air interface for [[UMTS frequency bands|UMTS]].

As NTT DoCoMo did not wait for the finalisation of the 3G Release 99 specification, their network was initially incompatible with UMTS.<ref>{{citation|author=Hsiao-Hwa Chen|title=The Next Generation CDMA Technologies|publisher=John Wiley and Sons|year=2007|isbn=978-0-470-02294-8|pages=105–106}}</ref> However, this has been resolved by NTT DoCoMo updating their network.

Code-Division Multiple Access communication networks have been developed by a number of companies over the years, but development of cell-phone networks based on CDMA (prior to W-CDMA) was dominated by [[Qualcomm]], the first company to succeed in developing a practical and cost-effective CDMA implementation for consumer cell phones and its early [[cdmaOne|IS-95]] air interface standard has evolved into the current CDMA2000 (IS-856/IS-2000) standard. Qualcomm created an experimental wideband CDMA system called CDMA2000 3x which unified the W-CDMA ([[3rd Generation Partnership Project|3GPP]]) and CDMA2000 ([[3rd Generation Partnership Project 2|3GPP2]]) network technologies into a single design for a worldwide standard air interface. Compatibility with CDMA2000 would have beneficially enabled roaming on existing networks beyond Japan, since Qualcomm CDMA2000 networks are widely deployed, especially in the Americas, with coverage in 58 countries {{as of|2006|lc=on}}. However, divergent requirements resulted in the W-CDMA standard being retained and deployed globally. W-CDMA has then become the dominant technology with 457 commercial networks in 178 countries as of April 2012.<ref>{{cite web|url=http://www.gsacom.com/downloads/pdf/HSPA_operator_commitments_160412.php4|title=GSM Association HSPA Market update April 2012}}</ref> Several CDMA2000 operators have even converted their networks to W-CDMA for international roaming compatibility and smooth upgrade path to [[LTE (telecommunication)|LTE]].

Despite incompatibility with existing air-interface standards, late introduction and the high upgrade cost of deploying an all-new transmitter technology, W-CDMA has become the dominant standard.

==== Rationale for W-CDMA ====
W-CDMA transmits on a pair of 5&nbsp;MHz-wide radio channels, while CDMA2000 transmits on one or several pairs of 1.25&nbsp;MHz radio channels. Though W-CDMA does use a [[direct-sequence spread spectrum|direct-sequence]] CDMA transmission technique like CDMA2000, W-CDMA is not simply a wideband version of CDMA2000 and differs in many aspects from CDMA2000. From an engineering point of view, W-CDMA provides a different balance of trade-offs between cost, capacity, performance, and density{{citation needed|date=November 2011}}; it also promises to achieve a benefit of reduced cost for video phone handsets. W-CDMA may also be better suited for deployment in the very dense cities of Europe and Asia. However, hurdles remain, and [[cross-licensing]] of [[patent]]s between Qualcomm and W-CDMA vendors has not eliminated possible patent issues due to the features of W-CDMA which remain covered by Qualcomm patents.<ref>{{cite web|url=https://www.infoworld.com/article/2205181/qualcomm-says-it-doesn-t-need-nokia-patents-2.html|title=Qualcomm says it doesn't need Nokia patents}}</ref>

W-CDMA has been developed into a complete set of specifications, a detailed protocol that defines how a mobile phone communicates with the tower, how signals are modulated, how datagrams are structured, and system interfaces are specified allowing free competition on technology elements.

==== Deployment ====
The world's first commercial W-CDMA service, FOMA, was launched by NTT DoCoMo in [[Japan]] in 2001.

Elsewhere, W-CDMA deployments are usually marketed under the UMTS brand.

W-CDMA has also been adapted for use in satellite communications on the U.S. [[Mobile User Objective System]] using geosynchronous satellites in place of cell towers.

[[J-Phone]] Japan (once [[Vodafone]] and now [[SoftBank Mobile]]) soon followed by launching their own W-CDMA based service, originally branded "Vodafone Global Standard" and claiming UMTS compatibility. The name of the service was changed to "Vodafone 3G" (now "SoftBank 3G") in December 2004.

Beginning in 2003, [[Hutchison Whampoa]] gradually launched their upstart UMTS networks.
 
Most countries have, since the ITU approved of the 3G mobile service, either "auctioned" the radio frequencies to the company willing to pay the most, or conducted a "beauty contest"{{snd}} asking the various companies to present what they intend to commit to if awarded the licences. This strategy has been criticised for aiming to drain the cash of operators to the brink of bankruptcy in order to honour their bids or proposals. Most of them have a time constraint for the rollout of the service{{snd}} where a certain "coverage" must be achieved within a given date or the licence will be revoked.

Vodafone launched several UMTS networks in Europe in February 2004. [[MobileOne]] of [[Singapore]] commercially launched its 3G (W-CDMA) services in February 2005. [[New Zealand]] in August 2005 and [[Australia]] in October 2005.

[[AT&T Mobility]] utilized a UMTS network, with HSPA+, from 2005 until its shutdown in February 2022.

Rogers in [[Canada]] March 2007 has launched HSDPA in the Toronto Golden Horseshoe district on W-CDMA at 850/1900&nbsp;MHz and plan the launch the service commercial in the top 25 cities October, 2007.

[[TeliaSonera]] opened W-CDMA service in [[Finland]] October 13, 2004, with speeds up to 384&nbsp;kbit/s. Availability only in main cities. Pricing is approx. €2/MB.{{Citation needed|date=January 2009}}

[[SK Telecom]] and [[KTF]], two largest mobile phone service providers in [[South Korea]], have each started offering W-CDMA service in December 2003. Due to poor coverage and lack of choice in handhelds, the W-CDMA service has barely made a dent in the Korean market which was dominated by CDMA2000. By October 2006 both companies are covering more than 90 cities while [[SK Telecom]] has announced that it will provide nationwide coverage for its WCDMA network in order for it to offer SBSM (Single Band Single Mode) handsets by the first half of 2007. [[KT Freecel]] will thus cut funding to its CDMA2000 network development to the minimum.

In [[Norway]], [[Telenor]] introduced W-CDMA in major cities by the end of 2004, while their competitor, [[NetCom (Norway)|NetCom]], followed suit a few months later. Both operators have 98% national coverage on EDGE, but Telenor has parallel WLAN roaming networks on GSM, where the UMTS service is competing with this. For this reason Telenor is dropping support of their WLAN service in Austria (2006).

[[Maxis Communications]] and [[Celcom]], two mobile phone service providers in [[Malaysia]], started offering W-CDMA services in 2005.

In [[Sweden]], [[Telia Company|Telia]] introduced W-CDMA in March 2004.

=== UTRA-TDD ===
UMTS-TDD, an acronym for Universal Mobile Telecommunications System (UMTS){{Snd}} time-division duplexing (TDD), is a 3GPP standardized version of UMTS networks that use UTRA-TDD.<ref name="ts25.201"/> UTRA-TDD is a UTRA that uses [[time-division duplex]]ing for duplexing.<ref name="ts25.201"/> While a full implementation of UMTS, it is mainly used to provide Internet access in circumstances similar to those where [[WiMAX]] might be used.{{Citation needed|date=March 2009}} UMTS-TDD is not directly compatible with UMTS-FDD: a device designed to use one standard cannot, unless specifically designed to, work on the other, because of the difference in air interface technologies and frequencies used.{{Citation needed|date=March 2009}} It is more formally as IMT-2000 CDMA-TDD or IMT 2000 Time-Division (IMT-TD).<ref name="Forkel">{{cite conference |title=Performance Comparison Between UTRA-TDD High Chip Rate And Low Chip Rate Operation |last1=Forkel |first1=I. |first2=Xin |last2=Jin |conference=The 13th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications |year=2002 |doi=10.1109/PIMRC.2002.1046515 |location=Pavilhao Altantico, Lisboa, Portugal |citeseerx = 10.1.1.11.3672}}</ref><ref name="whatistdscdma" />

The two UMTS air interfaces (UTRAs) for UMTS-TDD are TD-CDMA and TD-SCDMA. Both air interfaces use a combination of two channel access methods, [[code-division multiple access]] (CDMA) and time-division multiple access (TDMA): the frequency band is divided into time slots (TDMA), which are further divided into channels using CDMA spreading codes. These air interfaces are classified as TDD, because time slots can be allocated to either uplink or downlink traffic.

==== TD-CDMA (UTRA-TDD 3.84 Mcps High Chip Rate (HCR)) ====
[[TD-CDMA]], an acronym for Time-Division-[[code-division multiple access|Code-Division Multiple Access]], is a channel-access method based on using [[spread spectrum|spread-spectrum]] multiple-access (CDMA) across multiple time slots ([[time-division multiplexing|TDMA]]). TD-CDMA is the channel access method for UTRA-TDD HCR, which is an acronym for UMTS Terrestrial Radio Access-Time Division Duplex High Chip Rate.<ref name="Forkel"/>

UMTS-TDD's air interfaces that use the TD-CDMA channel access technique are standardized as UTRA-TDD HCR, which uses increments of 5&nbsp;[[MHz]] of spectrum, each slice divided into 10&nbsp;ms frames containing fifteen time slots (1500 per second).<ref name="Forkel"/> The time slots (TS) are allocated in fixed percentage for downlink and uplink. TD-CDMA is used to multiplex streams from or to multiple transceivers. Unlike W-CDMA, it does not need separate frequency bands for up- and downstream, allowing deployment in tight [[frequency band]]s.<ref>{{cite web|title=UMTS World TD-CDMA information|url=http://www.umtsworld.com/technology/tdcdma.htm|publisher=umtsworld.com|access-date=2008-02-28}}</ref>

TD-CDMA is a part of IMT-2000, defined as IMT-TD Time-Division (IMT CDMA TDD), and is one of the three UMTS air interfaces (UTRAs), as standardized by the 3GPP in UTRA-TDD HCR. UTRA-TDD HCR is closely related to W-CDMA, and provides the same types of channels where possible. UMTS's HSDPA/HSUPA enhancements are also implemented under TD-CDMA.<ref>{{cite web|title=IPWireless Ships First Commercial 3GPP Chipset with Full HSDPA Implementation|url=http://www.ipwireless.com/news/press_020805.html|publisher=ipwireless.com|access-date=2008-02-28 |archive-url = https://web.archive.org/web/20070927010536/http://www.ipwireless.com/news/press_020805.html <!-- Bot retrieved archive --> |archive-date = 2007-09-27}}</ref>

In the United States, the technology has been used for public safety and government use in the [[New York City]] and a few other areas.{{needs update|date=October 2023}}<ref>{{cite web|url=http://www.fiercewireless.com/tech/ipwireless-introduces-td-cdma-network-a-box-targeting-rural-operators-public-safety|title=IPWireless introduces TD-CDMA Network in a Box targeting rural operators, public safety |website=Fiercewireless |date=2 May 2010 }}</ref> In Japan, IPMobile planned to provide TD-CDMA service in year 2006, but it was delayed, changed to TD-SCDMA, and bankrupt before the service officially started.

==== TD-SCDMA (UTRA-TDD 1.28 Mcps Low Chip Rate (LCR)) ====
[[TD-SCDMA|Time-Division Synchronous Code-Division Multiple Access]] (TD-SCDMA) or UTRA TDD 1.28 [[Cycle per second|Mcps]] low chip rate (UTRA-TDD LCR)<ref name="whatistdscdma">{{cite web|url=http://www.tdscdma-forum.org/en/pdfword/200511817463050335.pdf|archive-url=https://web.archive.org/web/20140330050828/http://www.tdscdma-forum.org/en/pdfword/200511817463050335.pdf|archive-date=2014-03-30|title=TD-SCDMA Whitepaper: the Solution for TDD bands|author=Siemens|publisher=TD Forum|access-date=2009-06-15|date=2004-06-10|pages=6–9}}</ref><ref name="ituover"/> is an air interface<ref name="whatistdscdma"/> found in UMTS mobile telecommunications networks in China as an alternative to W-CDMA.

TD-SCDMA uses the TDMA channel access method combined with an adaptive [[synchronous CDMA]] component<ref name="whatistdscdma"/> on 1.6&nbsp;MHz slices of spectrum, allowing deployment in even tighter frequency bands than TD-CDMA. It is standardized by the 3GPP and also referred to as "UTRA-TDD LCR". However, the main incentive for development of this Chinese-developed standard was avoiding or reducing the license fees that have to be paid to non-Chinese patent owners. Unlike the other air interfaces, TD-SCDMA was not part of UMTS from the beginning but has been added in Release 4 of the specification.

Like TD-CDMA, TD-SCDMA is known as IMT CDMA TDD within IMT-2000.

The term "TD-SCDMA" is misleading. While it suggests covering only a channel access method, it is actually the common name for the whole air interface specification.<ref name="ituover"/>

TD-SCDMA / UMTS-TDD (LCR) networks are incompatible with W-CDMA / UMTS-FDD and TD-CDMA / UMTS-TDD (HCR) networks.

===== Objectives =====
TD-SCDMA was developed in the People's Republic of China by the Chinese Academy of Telecommunications Technology (CATT), [[Datang Telecom]] and [[Siemens]] in an attempt to avoid dependence on Western technology. This is likely primarily for practical reasons, since other 3G formats require the payment of patent fees to a large number of Western patent holders.

TD-SCDMA proponents also claim it is better suited for densely populated areas.<ref name="whatistdscdma"/> Further, it is supposed to cover all usage scenarios, whereas W-CDMA is optimised for symmetric traffic and macro cells, while TD-CDMA is best used in low mobility scenarios within micro or pico cells.<ref name="whatistdscdma"/>

TD-SCDMA is based on spread-spectrum technology which makes it unlikely that it will be able to completely escape the payment of license fees to western patent holders. The launch of a national TD-SCDMA network was initially projected by 2005<ref>{{cite web |url=https://archive.eetasia.com/www.eetasia.com/ART_8800451183_499488_NT_f43f85da.HTM?from=ART_Next |title=3G in China still held up |first=Mike |last=Clendenin |date=30 January 2007 |website=[[EE Times]]|archive-url=https://web.archive.org/web/20230421193717/https://archive.eetasia.com/www.eetasia.com/ART_8800451183_499488_NT_f43f85da.HTM?from=ART_Next |archive-date=21 April 2023 |url-status=dead}}</ref> but only reached large scale commercial trials with 60,000 users across eight cities in 2008.<ref>{{cite web |url=http://www.cellular-news.com/story/30163.php |title=China Mobile to Test TD-SCDMA on 60,000 Phones From April 1 |website=Cellular News |archive-url=https://web.archive.org/web/20080628212138/http://www.cellular-news.com/story/30163.php |archive-date=2008-06-28 |url-status=dead}}</ref>

On January 7, 2009, China granted a TD-SCDMA 3G licence to [[China Mobile]].<ref>{{cite web |url=https://www.reuters.com/article/oukin-uk-telecoms-china-idUKTRE5061KP20090107 |title=China issues 3G licences to main carriers |first=Michael |last=Wei |date=January 7, 2009 |website=Reuters}}</ref>

On September 21, 2009, China Mobile officially announced that it had 1,327,000 TD-SCDMA subscribers as of the end of August, 2009.

TD-SCDMA is not commonly used outside of China.<ref>{{cite web |url=https://www.electronics-notes.com/articles/connectivity/3g-umts/td-scdma.php |title=What is 3G TD-SCDMA |website=Electronics Notes}}</ref>

===== Technical highlights =====
TD-SCDMA uses TDD, in contrast to the FDD scheme used by [[W-CDMA]]. By dynamically adjusting the number of timeslots used for downlink and [[uplink]], the system can more easily accommodate asymmetric traffic with different data rate requirements on downlink and uplink than FDD schemes. Since it does not require paired spectrum for downlink and uplink, spectrum allocation flexibility is also increased. Using the same carrier frequency for uplink and downlink also means that the channel condition is the same on both directions, and the [[base station]] can deduce the downlink channel information from uplink channel estimates, which is helpful to the application of [[beamforming]] techniques.

TD-SCDMA also uses TDMA in addition to the CDMA used in WCDMA. This reduces the number of users in each timeslot, which reduces the implementation complexity of [[multiuser detection]] and beamforming schemes, but the non-continuous transmission also reduces [[coverage (telecommunication)|coverage]] (because of the higher peak power needed), mobility (because of lower [[power control]] frequency) and complicates [[radio resource management]] algorithms.

The "S" in TD-SCDMA stands for "synchronous", which means that uplink signals are synchronized at the base station receiver, achieved by continuous timing adjustments. This reduces the [[Interference (communication)|interference]] between users of the same timeslot using different codes by improving the [[Orthogonality#Telecommunications|orthogonality]] between the codes, therefore increasing system capacity, at the cost of some hardware complexity in achieving uplink synchronization.

===== History =====
On January 20, 2006, [[Ministry of Information Industry]] of the People's Republic of China formally announced that TD-SCDMA is the country's standard of 3G mobile telecommunication. On February 15, 2006, a timeline for deployment of the network in China was announced, stating pre-commercial trials would take place starting after completion of a number of test networks in select cities. These trials ran from March to October, 2006, but the results were apparently unsatisfactory. In early 2007, the Chinese government instructed the dominant cellular carrier, China Mobile, to build commercial trial networks in eight cities, and the two fixed-line carriers, [[China Telecom]] and [[China Netcom]], to build one each in two other cities. Construction of these trial networks was scheduled to finish during the fourth quarter of 2007, but delays meant that construction was not complete until early 2008.

The standard has been adopted by 3GPP since Rel-4, known as "UTRA TDD 1.28&nbsp;Mcps Option".<ref name="whatistdscdma" />

On March 28, 2008, China Mobile Group announced TD-SCDMA "commercial trials" for 60,000 test users in eight cities from April 1, 2008. Networks using other 3G standards (WCDMA and CDMA2000 EV/DO) had still not been launched in China, as these were delayed until TD-SCDMA was ready for commercial launch.

In January 2009, the [[Ministry of Industry and Information Technology of the People's Republic of China|Ministry of Industry and Information Technology]] (MIIT) in China took the unusual step of assigning licences for 3 different third-generation mobile phone standards to three carriers in a long-awaited step that is expected to prompt $41 billion in spending on new equipment. The Chinese-developed standard, TD-SCDMA, was assigned to China Mobile, the world's biggest phone carrier by subscribers. That appeared to be an effort to make sure the new system has the financial and technical backing to succeed. Licences for two existing 3G standards, W-CDMA and [[Evolution-Data Optimized|CDMA2000 1xEV-DO]], were assigned to [[China Unicom]] and China Telecom, respectively. Third-generation, or 3G, technology supports Web surfing, wireless video and other services and the start of service is expected to spur new revenue growth.

The technical split by MIIT has hampered the performance of China Mobile in the 3G market, with users and China Mobile engineers alike pointing to the lack of suitable handsets to use on the network.<ref>{{cite news |last1=Lau |first1=Justine |title=China Mobile trails on 3G technology |url=https://www.ft.com/content/f25fb1a6-7461-11dd-bc91-0000779fd18c |archive-url=https://ghostarchive.org/archive/20221210/https://www.ft.com/content/f25fb1a6-7461-11dd-bc91-0000779fd18c |archive-date=2022-12-10 |url-access=subscription |url-status=live |work=Financial Times |date=August 28, 2008}}{{subscription required}}</ref> Deployment of base stations has also been slow, resulting in lack of improvement of service for users.<ref>{{cite web |title=China's 3G Network Deployment Update{{Snd}} IHS Technology |url=https://technology.ihs.com/393444/chinas-3g-network-deployment-update |website=IHS Market: Technology |access-date=9 August 2019 |archive-date=9 August 2019 |archive-url=https://web.archive.org/web/20190809132931/https://technology.ihs.com/393444/chinas-3g-network-deployment-update |url-status=dead }}</ref> The network connection itself has consistently been slower than that from the other two carriers, leading to a sharp decline in market share. By 2011 China Mobile has already moved its focus onto TD-LTE.<ref>{{cite web |title=China Mobile Not Serious About TD-SCDMA, Betting Big on TD-LTE |url=https://technode.com/2011/05/09/china-mobile-not-serious-td-scdma-bet-big-ontd-lte/ |website=TechNode |date=9 May 2011}}</ref><ref name="CM TD-SCDMA CN 2"/> Gradual closures of TD-SCDMA stations started in 2016.<ref>{{cite web |date=2016|title=Closing of China Mobile 3G Base Stations Signifies End of China's Self-owned Standard |url=http://en.people.cn/n3/2016/0316/c90000-9030605.html |website=People's Daily Online }}</ref><ref name="CM TD-SCDMA CN 1"/>

===== Frequency bands & Deployments =====
{{further|UMTS frequency bands}}
The following is a list of [[mobile telephony|mobile telecommunications]] networks using third-generation TD-SCDMA / UMTS-TDD (LCR) technology.

{|class="wikitable sortable"
|-
! Operator
! Country
! Frequency<br />(MHz)
! Band
! Launch date
! class="sortable" | Notes
|-
| China Mobile
| {{flag|China}}
| 2100
| A+<br /><small>(Band 34)</small>
| {{dts|Jan 2009}}
| (↓↑) 2010–2025&nbsp;MHz<br />{{fontcolour|red|Network is being phased out and is to be shutdown by 2025.}}<br /><ref name="CM TD-SCDMA Launch CN">{{cite web |url=http://www.spreadtrum.com/en/news/press-releases/pr2008-03-28 |title=China Mobile Announces Commercial Deployment of TD-SCDMA Technology |publisher=Spreadtrum Communications, Inc. |date=2008-03-28 |access-date=2014-07-17 |archive-date=2014-07-25 |archive-url=https://web.archive.org/web/20140725141648/http://www.spreadtrum.com/en/news/press-releases/pr2008-03-28 |url-status=dead}}</ref><ref name="CM TD-SCDMA CN 1">{{cite web|url=http://english.caixin.com/2014-12-15/100762382.html |title=China Mobile's Dead End on the 3G Highway |publisher=CaixinOnline |date=2014-12-15 |access-date=2016-12-17}}</ref><ref name="CM TD-SCDMA CN 2">{{cite web|url=http://english.caixin.com/2016-03-14/100920062.html |title=China Mobile Said to Begin Closing Its 3G Base Stations |publisher=CaixinOnline |date=2016-03-14 |access-date=2016-12-17}}</ref>
|-
| {{fontcolour|grey|China Mobile}}
| {{flag|China}}
| {{fontcolour|grey|1900}}
| {{fontcolour|grey|A−<br /><small>(Band 33)</small>}}
| {{fontcolour|grey|{{dts|Jan 2009}} - {{dts|Dec 2013}}}}
| {{fontcolour|grey|(↓↑) 1900–1920&nbsp;MHz (Subset of Band 39)<br />Network upgraded to TDD-LTE (B39) via RRU Software Update.<br /><ref name="CM TD-SCDMA Launch CN"/><ref name="CM TD-SCDMA CN 1" /><ref name="CM TD-SCDMA CN 2" /><ref name="CM TD-SCDMA CN 3">{{cite web|url=https://www.gsma.com/solutions-and-impact/technologies/internet-of-things/wp-content/uploads/2013/03/Presentation-5-Madame-Hunag-China-Mobile.pdf |title=Implementing LTE FDD/TDD Convergence Network in the age of Mobile Inter net |publisher=China Mobile |date=2013-06-01 |access-date=2024-08-31}}</ref>}}
|-
| {{fontcolour|grey|''none''}}
| {{flag|China}}
| {{fontcolour|grey|1900}}
| {{fontcolour|grey|F<br /><small>(Band 39)</small>}}
| {{fontcolour|grey|''N/A''}}
| {{fontcolour|grey|(↓↑) 1880–1920&nbsp;MHz<br />No deployments, later used for TD-LTE instead.<br />Upper half previously used by [[Personal Handy-phone System|Xiaolingtong (PHS)]]}}
|-
| {{fontcolour|grey|China Mobile}}
| {{flag|China}}
| {{fontcolour|grey|2300}}
| {{fontcolour|grey|E<br /><small>(Band 40)</small>}}
| {{fontcolour|grey|{{dts|Jan 2009}} - {{dts|Dec 2013}}}}
| {{fontcolour|grey|(↓↑) 2300–2400&nbsp;MHz<br />Network upgraded to TDD-LTE (B40) via RRU Software Update.<br /><ref name="CM TD-SCDMA Launch CN"/><ref name="CM TD-SCDMA CN 1" /><ref name="CM TD-SCDMA CN 2" /><ref name="CM TD-SCDMA CN 3" />}}
|}

==== Unlicensed UMTS-TDD ====
In Europe, [[European Conference of Postal and Telecommunications Administrations|CEPT]] allocated the 2010–2020&nbsp;MHz range for a variant of UMTS-TDD designed for unlicensed, self-provided use.<ref>{{cite web|title=ERC/DEC/(99)25 EU Recommendation on UMTS TDD|url=http://www.ero.dk/documentation/docs/doc98/official/pdf/DEC9925E.PDF|publisher=ero.dk|access-date=2008-02-28}}</ref> Some telecom groups and jurisdictions have proposed withdrawing this service in favour of licensed UMTS-TDD,<ref>{{cite web|title=Award_of_available_spectrum:_2500-2690_MHz,_2010-2025_MHz_and_2290-2300_MHz|url=http://www.ofcom.org.uk/consult/condocs/2ghzawards/2ghzawards.pdf|publisher=ofcom.org.uk|access-date=2008-02-28 |archive-url = https://web.archive.org/web/20070930030814/http://www.ofcom.org.uk/consult/condocs/2ghzawards/2ghzawards.pdf |archive-date = 2007-09-30 |url-status=dead}}</ref> due to lack of demand, and lack of development of a UMTS TDD air interface technology suitable for deployment in this band.

==== Comparison with UMTS-FDD ====
Ordinary UMTS uses UTRA-FDD as an air interface and is known as [[UMTS-FDD]]. UMTS-FDD uses W-CDMA for multiple access and [[frequency-division duplex]] for duplexing, meaning that the up-link and down-link transmit on different frequencies. UMTS is usually transmitted on frequencies assigned for [[1G]], [[2G]], or 3G mobile telephone service in the countries of operation.

UMTS-TDD uses time-division duplexing, allowing the up-link and down-link to share the same spectrum. This allows the operator to more flexibly divide the usage of available spectrum according to traffic patterns. For ordinary phone service, you would expect the up-link and down-link to carry approximately equal amounts of data (because every phone call needs a voice transmission in either direction), but Internet-oriented traffic is more frequently one-way. For example, when browsing a website, the user will send commands, which are short, to the server, but the server will send whole files, that are generally larger than those commands, in response.

UMTS-TDD tends to be allocated frequency intended for mobile/wireless Internet services rather than used on existing cellular frequencies. This is, in part, because TDD duplexing is not normally allowed on [[Mobile phone|cellular]], [[Personal Communications Service|PCS]]/PCN, and 3G frequencies. TDD technologies open up the usage of left-over unpaired spectrum.

Europe-wide, several bands are provided either specifically for UMTS-TDD or for similar technologies. These are 1900&nbsp;MHz and 1920&nbsp;MHz and between 2010&nbsp;MHz and 2025&nbsp;MHz. In several countries the 2500{{En dash}}2690&nbsp;MHz band (also known as MMDS in the USA) have been used for UMTS-TDD deployments. Additionally, spectrum around the 3.5&nbsp;GHz range has been allocated in some countries, notably Britain, in a technology-neutral environment. In the Czech Republic UTMS-TDD is also used in a frequency range around 872&nbsp;MHz.<ref>{{cite web|title=T-Mobile launches UMTS TDD network in the Czech Republic|url=http://www.geekzone.co.nz/content.asp?contentid=4693|date=21 June 2005}}</ref>

==== Deployment ====
UMTS-TDD has been deployed for public and/or private networks in at least nineteen countries around the world, with live systems in, amongst other countries, Australia, Czech Republic, France, Germany, Japan, New Zealand, Botswana, South Africa, the UK, and the USA.

Deployments in the US thus far have been limited. It has been selected for a public safety support network used by emergency responders in New York,<ref>{{cite web|title=Northrop Grumman Wins $500 Million New York City Broadband Mobile Wireless Contract|url=http://www.ipwireless.com/news/press_091206.html|publisher=ipwireless.com|access-date=2008-02-28|archive-date=2007-11-24|archive-url=https://web.archive.org/web/20071124072118/http://www.ipwireless.com/news/press_091206.html|url-status=dead}}</ref> but outside of some experimental systems, notably one from [[Nextel]], thus far the WiMAX standard appears to have gained greater traction as a general mobile Internet access system.

==== Competing standards ====
A variety of Internet-access systems exist which provide broadband speed access to the net. These include WiMAX and [[HIPERMAN]]. UMTS-TDD has the advantages of being able to use an operator's existing UMTS/GSM infrastructure, should it have one, and that it includes UMTS modes optimized for circuit switching should, for example, the operator want to offer telephone service. UMTS-TDD's performance is also more consistent. However, UMTS-TDD deployers often have regulatory problems with taking advantage of some of the services UMTS compatibility provides. For example, the UMTS-TDD spectrum in the UK cannot be used to provide telephone service, though the regulator [[OFCOM]] is discussing the possibility of allowing it at some point in the future. Few operators considering UMTS-TDD have existing UMTS/GSM infrastructure.

Additionally, the WiMAX and HIPERMAN systems provide significantly larger bandwidths when the mobile station is near the tower.

Like most mobile Internet access systems, many users who might otherwise choose UMTS-TDD will find their needs covered by the ad hoc collection of unconnected Wi-Fi access points at many restaurants and transportation hubs, and/or by Internet access already provided by their mobile phone operator. By comparison, UMTS-TDD (and systems like WiMAX) offers mobile, and more consistent, access than the former, and generally faster access than the latter.