TD-SCDMA
Encyclopedia
Time Division Synchronous Code Division Multiple Access
(TD-SCDMA) or UTRA/UMTS-TDD 1.28 Mcps Low Chip Rate (LCR), is an air interface
found in UMTS mobile telecommunications networks in China as an alternative to W-CDMA
. Together with TD-CDMA
, it is also known as UMTS-TDD or IMT 2000 Time-Division (IMT-TD).
The term "TD-SCDMA" is misleading. While it suggests covering only a channel access method based on CDMA, it is actually the common name for the whole air interface specification.
TD-SCDMA uses the S-CDMA channel access method
across multiple time slots.
by the Chinese Academy of Telecommunications Technology (CATT), Datang Telecom, and Siemens AG
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. 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.
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 but only reached large scale commercial trials with 60,000 users across eight cities in 2008.
On January 7, 2009, China granted a TD-SCDMA 3G licence to China Mobile
.
On September 21, 2009, China Mobile officially announced that it had 1,327,000 TD-SCDMA subscribers as of the end of August, 2009.
While TD is primarily a China-only system, it may well be exported to developing countries. It is likely to be replaced with a newer TD-LTE system over the next 5 years.
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 1.28Mcps Option".
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) have 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 (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 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.
. 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
(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
between users of the same timeslot using different codes by improving the orthogonality between the codes, therefore increasing system capacity, at the cost of some hardware complexity in achieving uplink synchronization.
Code division multiple access
Code division multiple access is a channel access method used by various radio communication technologies. It should not be confused with the mobile phone standards called cdmaOne, CDMA2000 and WCDMA , which are often referred to as simply CDMA, and use CDMA as an underlying channel access...
(TD-SCDMA) or UTRA/UMTS-TDD 1.28 Mcps Low Chip Rate (LCR), is an air interface
Air interface
In mobile or wireless communication, the air interface is the radio-based communication link between the mobile station and the active base station...
found in UMTS mobile telecommunications networks in China as an alternative to W-CDMA
W-CDMA
W-CDMA , UMTS-FDD, UTRA-FDD, or IMT-2000 CDMA Direct Spread is an air interface standard found in 3G mobile telecommunications networks. It is the basis of Japan's NTT DoCoMo's FOMA service and the most-commonly used member of the UMTS family and sometimes used as a synonym for UMTS...
. Together with TD-CDMA
TD-CDMA
TD-CDMA, an acronym for Time-division - CDMA, is a channel access method based on using spread spectrum across multiple time slots. It is shown that a mixture of TDMA and CDMA provides better quality of service for multimedia communications in terms of data throughput and voice/video...
, it is also known as UMTS-TDD or IMT 2000 Time-Division (IMT-TD).
The term "TD-SCDMA" is misleading. While it suggests covering only a channel access method based on CDMA, it is actually the common name for the whole air interface specification.
TD-SCDMA uses the S-CDMA channel access method
Channel access method
In telecommunications and computer networks, a channel access method or multiple access method allows several terminals connected to the same multi-point transmission medium to transmit over it and to share its capacity...
across multiple time slots.
Objectives
TD-SCDMA is being developed in the People's Republic of ChinaPeople's Republic of China
China , officially the People's Republic of China , is the most populous country in the world, with over 1.3 billion citizens. Located in East Asia, the country covers approximately 9.6 million square kilometres...
by the Chinese Academy of Telecommunications Technology (CATT), Datang Telecom, and Siemens AG
Siemens AG
Siemens AG is a German multinational conglomerate company headquartered in Munich, Germany. It is the largest Europe-based electronics and electrical engineering company....
in an attempt to avoid dependence on Western technology. This is likely primarily for practical reasons, since other 3G
3G
3G or 3rd generation mobile telecommunications is a generation of standards for mobile phones and mobile telecommunication services fulfilling the International Mobile Telecommunications-2000 specifications by the International Telecommunication Union...
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. 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.
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 but only reached large scale commercial trials with 60,000 users across eight cities in 2008.
On January 7, 2009, China granted a TD-SCDMA 3G licence to China Mobile
China Mobile
China Mobile Limited is a Chinese state-owned telecommunication company that provides mobile voice and multimedia services through its nationwide mobile telecommunications network, the largest of its kind in the world...
.
On September 21, 2009, China Mobile officially announced that it had 1,327,000 TD-SCDMA subscribers as of the end of August, 2009.
While TD is primarily a China-only system, it may well be exported to developing countries. It is likely to be replaced with a newer TD-LTE system over the next 5 years.
Deployment and usage
On January 20, 2006, Ministry of Information Industry of the People's Republic of ChinaPeople's Republic of China
China , officially the People's Republic of China , is the most populous country in the world, with over 1.3 billion citizens. Located in East Asia, the country covers approximately 9.6 million square kilometres...
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
China Mobile
China Mobile Limited is a Chinese state-owned telecommunication company that provides mobile voice and multimedia services through its nationwide mobile telecommunications network, the largest of its kind in the world...
, to build commercial trial networks in eight cities, and the two fixed-line carriers, China Telecom
China Telecom
China Telecom Corp. Ltd. is a Chinese state-owned telecommunication company. It is the largest fixed line service and 3rd largest mobile telecommunication provider in the People's Republic of China.-Sectors:...
and China Netcom
China Netcom
China Netcom, full name China Netcom Group Corporation Limited , abbreviated CNC, was a former telecommunication service provider in People's Republic of China...
, 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
3GPP
The 3rd Generation Partnership Project is a collaboration between groups of telecommunications associations, known as the Organizational Partners...
since Rel-4, known as "UTRA TDD 1.28Mcps Option".
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) have 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 (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
W-CDMA
W-CDMA , UMTS-FDD, UTRA-FDD, or IMT-2000 CDMA Direct Spread is an air interface standard found in 3G mobile telecommunications networks. It is the basis of Japan's NTT DoCoMo's FOMA service and the most-commonly used member of the UMTS family and sometimes used as a synonym for UMTS...
and CDMA2000 1xEV-DO
Evolution-Data Optimized
Evolution-Data Optimized or Evolution-Data only is a telecommunications standard for the wireless transmission of data through radio signals, typically for broadband Internet access...
, 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.
Technical highlights
TD-SCDMA uses TDD, in contrast to the FDD scheme used by W-CDMAW-CDMA
W-CDMA , UMTS-FDD, UTRA-FDD, or IMT-2000 CDMA Direct Spread is an air interface standard found in 3G mobile telecommunications networks. It is the basis of Japan's NTT DoCoMo's FOMA service and the most-commonly used member of the UMTS family and sometimes used as a synonym for UMTS...
. By dynamically adjusting the number of timeslots used for downlink and uplink
Uplink
A telecommunications link is generally one of several types of information transmission paths such as those provided by communication satellites to connect two points on earth.-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
Base station
The term base station can be used in the context of land surveying and wireless communications.- Land surveying :In the context of external land surveying, a base station is a GPS receiver at an accurately-known fixed location which is used to derive correction information for nearby portable GPS...
can deduce the downlink channel information from uplink channel estimates, which is helpful to the application of beamforming
Beamforming
Beamforming is a signal processing technique used in sensor arrays for directional signal transmission or reception. This is achieved by combining elements in the array in a way where signals at particular angles experience constructive interference and while others experience destructive...
techniques.
TD-SCDMA also uses TDMA
Time division multiple access
Time division multiple access is a channel access method for shared medium networks. It allows several users to share the same frequency channel by dividing the signal into different time slots. The users transmit in rapid succession, one after the other, each using its own time slot. This...
in addition to the CDMA
Code division multiple access
Code division multiple access is a channel access method used by various radio communication technologies. It should not be confused with the mobile phone standards called cdmaOne, CDMA2000 and WCDMA , which are often referred to as simply CDMA, and use CDMA as an underlying channel access...
used in WCDMA. This reduces the number of users in each timeslot, which reduces the implementation complexity of multiuser detection
Multiuser detection
Multiuser detection is one of the receiver design technology for detecting desired signal from interference and noise. Traditionally single-user receiver is known suffering from the so-called near-far problem, where a near-by or strong signal source may block the signal receiption of far-away or...
and beamforming
Beamforming
Beamforming is a signal processing technique used in sensor arrays for directional signal transmission or reception. This is achieved by combining elements in the array in a way where signals at particular angles experience constructive interference and while others experience destructive...
schemes, but the non-continuous transmission also reduces coverage
Coverage (telecommunication)
In telecommunications, the coverage of a radio station is the geographic area where the station can communicate. Broadcasters and telecommunications companies frequently produce coverage maps to indicate to users the station's intended service area. Coverage depends on several factors, such as...
(because of the higher peak power needed), mobility (because of lower power control
Power control
Power control, broadly speaking, is the intelligent selection of transmit power in a communication system to achieve good performance within the system. The notion of "good performance" can depend on context and may include optimizing metrics such as link data rate, network capacity, geographic...
frequency) and complicates radio resource management
Radio resource management
Radio resource management is the system level control of co-channel interference and other radio transmission characteristics in wireless communication systems, for example cellular networks, wireless networks and broadcasting systems...
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
Interference (communication)
In communications and electronics, especially in telecommunications, interference is anything which alters, modifies, or disrupts a signal as it travels along a channel between a source and a receiver. The term typically refers to the addition of unwanted signals to a useful signal...
between users of the same timeslot using different codes by improving the orthogonality between the codes, therefore increasing system capacity, at the cost of some hardware complexity in achieving uplink synchronization.
See also
- W-CDMAW-CDMAW-CDMA , UMTS-FDD, UTRA-FDD, or IMT-2000 CDMA Direct Spread is an air interface standard found in 3G mobile telecommunications networks. It is the basis of Japan's NTT DoCoMo's FOMA service and the most-commonly used member of the UMTS family and sometimes used as a synonym for UMTS...
- TD-CDMATD-CDMATD-CDMA, an acronym for Time-division - CDMA, is a channel access method based on using spread spectrum across multiple time slots. It is shown that a mixture of TDMA and CDMA provides better quality of service for multimedia communications in terms of data throughput and voice/video...
- Dynamic TDMA
- Telecommunications industry in ChinaTelecommunications industry in ChinaThe telecommunications industry in China is dominated by three state-run businesses: China Telecom, China Unicom and China Mobile. The three companies were formed by a recent revolution and restructuring launched in May 2008, directed by Ministry of Information Industry , Nationals Development and...
- Communications in China
- Standardization in China
Documentation
- TS 25.201 Physical Layer - General Description - Describes basic differences between FDD and TDD.
- TS 25.221 Physical channels and mapping of transport channels onto physical channels (TDD)
- TS 25.222 Multiplexing and channel coding (TDD)
- TS 25.223 Spreading and modulation (TDD)
- TS 25.224 Physical layer procedures (TDD)
- TS 25.225 Physical layer - Measurements (TDD)
External links
- TD-SCDMA Forum
- TD-SCDMA Industry Alliance
- China will not interfere in 3G standard selection
- China will provide 3G Service in cities where Olympic Games 2008 are held