Development of TD-SCDMA in China

On 20th January, 2006, Ministry of Information Industry of the PRC formally announced that TD-SCDMA is the country's standard of 3G mobile telecommunication. On 15th February, 2006, a plan for deployment of TD-SCDMA in China was announced, some experiments would start after establishing some networks in those selected cities. These trials continued from March to October, 2006, but the results were apparently unsatisfactory. In early 2007, the largest mobile communication carrier in China, China Mobile built commercial trial networks in eight cities, and the two fixed-line carriers, China Telecom and China Netcom built one each in two other cities. It required that construction of these trial networks should be finished during the fourth quarter of 2007, but there were some delays.

On 28th March, 2008, China Mobile Group announced that TD-SCDMA will begin to use for 60,000 test users in eight selected cities from 1th April. Other 3G standards like WCDMA AND CDMA2000 will be delayed to implement until TD-SCDMA is success.

On 7th January, 2009 three main carriers: China Mobile Ltd., China Unicom Ltd. and China Telecom Corp. obtained the third-generation mobile phone licenses. They went to an agreement of long term plan to develop the standard and they would $41 billion in spending on new equipment.

In 2008, TD performed very well during the 29th Beijing Olympic Games, and gained the success of trial commercial service in Chinese 10 big cities. The standards for TD-LTE, the TD-SCDMA technology migration, have been almost fixed and the product development work is under its way. After gained TD license in Jan 2009, China Mobile issued timetable for TD network construction and subscriber development plan. TD is entering a new commercial history era.

The development of 3G standard took a lot of money and time because China's government wanted to develop its own technology to compete with two global 3G standards.The Chinese-developed standard, TD-SCDMA appeared to be an effort to make sure the new system has the financial and technical backing to succeed.

Advantages of TD-SCDMA Technology

Advantages of TD-SCDMA Technology can be listed as follows:

Flexible use of spectrum
Both WCDMA and cdma2000 belong to FDD system, requiring pair uplink and downlink frequency and protective space of de jure width, causing difficulty in frequency planning. For nationwide networking under FDD, it requires at least 15MHz*2 for both uplink and downlink, or 30M frequency. Under TD-SCDMA, the bandwidth of single carrier is only 1.6MHz. Besides, TDD requires no symmetrical band and can be placed anywhere. 20 MHz frequency is enough for building a nationwide network, with no less capacity than 30M FDD network.

Higher spectrum availability
WCDMA has 5MHz*2, or 10MHz bandwidth in each carrier to support about 60 path voice ( co-frequency and multi station networking), while TD-SCDMA can bear 6 carriers within 10 MHz bandwidth, with each supporting 20 paths voice simultaneously (co-frequency and multi-station networking), that is, supporting 120 voice within 10 MHz bandwidth. The spectrum efficiency of TD-SCDMA is double the level of WCDMA.

Especially good for data service
Under TDD, transmission of uplink and downlink data is decided by controlling the transmitting time length for uplink and downlink. The time length for transmitting and receiving can be flexibly controlled and altered. This feature is a special advantage for future efficient transmission of asymmetrical services such as mobile Internet and multi-media video on demand. Among Internet services, searching takes a quite large proportion but the amount of transmitting and receiving information is in obvious asymmetry as it processes little uplink data from terminal to base station but huge downlink data from base station to terminal. According to related estimation by ITU, by 2010, the proportion of uplink data and downlink data will reach 1 to 5. Only TDD can meet the requirement of efficient transmission of asymmetrical services by reducing uplink transmitting time and lengthen downlink receiving time through self-adaptive time slot adjustment. Such strength weak breathing effect, good for network planning and optimization . Due to its complex frequency features, services and its combination, complicated air environment and diversified premises, 3G system faces tremendous challenge in its network planning and optimization. CDMA system is a interference restricted system rather than resource restricted system, and its interference and coverage counteract against each other. Therefore, CDMA system has strong breathing effect, which is bad to network planning and optimization. Compared with FDD system, TD-SCDMA is a technology that can better avoid breathing effect, which greatly simplifying network planning and optimization. It can quickly respond to changes of user requirements for services and improve the overall network operation and efficiency.

Information security
So far, China’s telecommunications industry is still highly reliant on other countries. In certain areas, there are huge potential security hazards. For TD-SCDMA, as a 3G standard with our independent IPR, China owns the intellectual property rights of its core algorithm and can provide highest level encryption from base band algorithm to application layer, meeting confidential requirement for civil use, military network and governance. The dynamic beam forming of smart antenna boasts very strong tracking, anti-tracking and monitoring functions.

Reference
http://en.wikipedia.org/wiki/TD-SCDMA
TD-SCDMA Technology Strength http://www.tdscdma-forum.org/en/

Introduction of TD-SCDMA

TD-SCDMA （Time Division Synchronous Code Division Multiple Access）is a 3G wireless telecommunications standard raised by China Wireless Telecommunications Standard Group (CWTS) and developed by China Academy of Telecommunication Technology (CATT) and Siemens. TD-SCDMA is a kind of combination technology of three basic transmission modes, FDMA, TDMA and CDMA, featuring with large system capacity, high use rate of spectrum and strong anti-interference capability. The basement of TD-SCDMA is the network of GSM-MAP .

Comparing with the existed technology, TD-SCDMA technology has many advantages. As TD-SCDMA is a combination technology, it adopts advanced technology such as time division duplex, smart antenna, joint detection, baton handover, uplink synchronization and dynamic channel allocation (DCA).

Time Division Duplex：Time Division Duplex is a fundamental differentiator between TD-SCDMA and FDD. TD-SCDMA system, under TDD mode, enables uplink and downlink transmission in the same carrier, rather than symmetrical uplink and downlink spectrum as required by FDD. Apart from great improvement of the spectrum availability by fully leveraging spectrum resources, TDD mode also boasts the strength of flexible adjustment of uplink and downlink conversion point based on different service type, thus providing best service capacity and spectrum availability.

Smart Antenna: Smart Antenna system consists of a set of antenna array, its connected receiver and advanced digital signal processing algorithm, On the transmit side, the smart antenna produces phase difference on the antenna array based on the received signals, withdraws terminal location information, and effectively produces multiple beam forming, with each beam directing towards a specific terminal and moving with it automatically, thus reducing co-channel interference and improving downlink capacity. The space beam forming results in great deduction of the total RF transmission power with the cell coverage unchanged. It helps improve the space electro-magnetic environment on the one hand and reduce the cost of wireless base stations on the other. On the receiving side, the smart antenna, through space selection diversity, can greatly improve the receiving sensitivity and reduce co-channel interference of users in different locations. As a result, it can effectively consolidate multi-path component, offset multi-path fading and improve uplink capacity.

Joint Detection: Joint detection technology is an inhibitor to multi-user interference, a major technology for eliminating and reducing multi-user interference. It process all user signals as useful signals, thus fully utilizing information from user signal such as the spread code, amplitude, time setting and delay, greatly reduce multi-path and multi-access interference. Combining with smart antenna technology, the joint detection technology can achieve better desired results.

Baton Handover: Baton handover is one of the core technologies of TD-SCDMA mobile communications system. It is a new handover approach between hard handover and soft handover. The principle is to obtain information of transmission time and power in the uplink channel in advance by using uplink pre-sync technology during the handover measurement period, thus reduce handover time, improve success rate and reduce drop rate. The whole process is like a baton match in the field sports, so it is vividly granted a name of baton handover. Compared with hard handover and soft handover, baton handover boasts advantages of less handover time, requiring only one wireless link during the whole handover process, less wireless resources as compared with soft handover, higher success rate as compared with hard handover as the uplink and downlink handover run separately, and enabling harmless handover etc.

Uplink Synchronization: Uplink Synchronization refers to full synchronization of signals transmitted by various terminals at the uplink channel at the base station demodulator. This is enabled through software and physical layer design. It enables complete orthogonality of all path in orthogonal spread spectrum code during dispreading, thus producing no multi-access interference. It overcomes the bottleneck of asynchronous CDMA technology for interferences arising from non-orthogonal path due to different arriving time of signals transmitted by each mobile terminal to base stations, thus improving the TD-SCDMA system capacity and spectrum availability. It can also simplify hardware circuit and reduce cost. Dynamic Channel Allocation: Dynamic channel allocation technology adopted by TD-SCDMA enables flexible wireless allocation in time domain, space domain and code domain. This technology enables better avoidance of interference and minimum channel reuse distance of TD-SCDMA system, thus efficiently utilizing the limited wireless resources and improving the system capacity. In addition, dynamic channel allocation in time domain enables flexible allocation of time slot resources, dynamic adjustment of the number of uplink and downlink time slots, so as to support symmetrical and asymmetrical services flexibly.