Editing UMTS (section)

=== 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.