The standard and development of 3g

With the rapid development of communication service and the surge of traffic, the future mobile communication system should not only have large system capacity, but also can support the effective transmission of voice, data, image, multimedia and other services. The third generation mobile communication system combines high speed mobile access and internet-based protocol services to provide users with more economical and richer wireless communication services while increasing the wireless frequency utilization.

The third generation mobile communication systems are collectively referred to as IMT-2000 (3G) in the International Telecommunication Union (ITU) in 1985 to work on the 2000MHz band system. Compared with the first generation analog mobile communication and the second-generation digital mobile communication system, the third generation's main feature is that it can provide mobile multimedia service.

The third generation of mobile communications mainstream technical standards are three: IMT-2000 cdma-ds (IMT-2000 Direct spread-spectrum CDMA), that is, WCDMA, it can be in a bandwidth of up to 5MHz in the frequency of direct spread of the signal IMT-2000CDMA-MC (IMT-2000 Multicarrier CDMA), that is, CDMA2000, a technology proposed by the United States, It is a broadband system consisting of one or more 1.25MHz narrowband direct spread spectrum systems, and TD-SCDMA (Time Division Synchronous Code Division Multiple Access) is proposed by China and is a member of the CDMATDD standard. (Computer science)

1.WCDMA

The WCDMA (wideband CDMA) standard is established by 3GPP organization, its main characteristic is the wireless access network uses WCDMA technology, the core network divides into the circuit domain and the grouping domain, respectively supports the voice service and the data service, and proposes the Open service access (OSA) the concept.

WCDMA technical advantages mainly have the following: (1) Business flexibility. WCDMA allows each 5MHz carrier to handle mixed operations from 8kbWs to 2MBIT/S. In addition, both circuit switching service and packet switching service can be carried out on the same channel, and the real multimedia service is realized by using multiple circuits and packet switching connections on a single terminal. You can support business with different quality requirements, such as voice and packet data, and ensure high quality and perfect coverage. (2) High spectrum efficiency. WCDMA can efficiently use the radio spectrum. Since it uses single cell multiplexing, frequency planning is not required. The network capacity can be greatly improved by using the layered cell structure, adaptive antenna array and coherent demodulation (bidirectional) technology. (3) Capacity and wide coverage. WCDMA RF Transceiver can handle the voice users are typical narrowband transceiver 8 times times. Each RF carrier can handle 80 simultaneous voice calls or 50 simultaneous Internet data users. WCDMA capacity is almost twice times that of Narrowband CDMA. Greater bandwidth allows for lower receiver thresholds using coherent demodulation and fast power control in up/down links. (4) Each connection can provide a variety of business. WCDMA meets the real umts/imt-2000 requirements. Packet and circuit switching services can be freely blended within different bandwidth and can be provided to the same user at the same time. Each WCDMA terminal can simultaneously access up to 6 different businesses, which can be a combination of voice or fax, e-mail, and video data services. (5) Seamless gsm/umts access. The dual-mode terminal will provide seamless switching and roaming between the GSM network and the UMTS/IMT-2000 network, with as large a business image as possible between the two access systems. (6) The economy and simplicity of the terminal. The signal processing required by WCDMA mobile phones is about 1/10 of the composite TD/CDMA technology. Simpler, more economical terminals are prone to mass production, resulting in higher economies of scale, more competition, and greater choice for network operators and users.

2.cdma2000

CDMA2000 is one of the third generation mobile communication wireless transmission technologies stipulated by the International Telecommunication Union (ITU), which is derived from the narrow-band CDMA first digital standard, and can be upgraded directly from the original CDMA one structure to 3G, and the construction cost is low. According to the bandwidth used to differentiate, CDMA2000 can be divided into 1x systems and 3x systems. 1x system uses 1.25MHz bandwidth, the highest data service rate can reach 307kbit/s. After the 1x system, the internationally accepted development direction is 1x ev-do and 1x EV-DV system. The 1x ev-do system focuses on improving the performance of the data service and raising the user's maximum data service transfer rate to 2.4mbit/s. While the 1x EV-DV system increases the maximum rate of data service to 3.1mbit/s, it further improves the capacity of voice service.

Although CDMA2000 's supporters are not as much as WCDMA, CDMA2000 technology is the fastest-growing of the standards, and many 3G handsets have been pioneered.

The technical feature of CDMA2000 is that it has multiple channel bandwidth. The forward link supports both Multicarrier (MC) and Dsss (DS), and the reverse link only supports the direct spread mode. When using Multi-carrier mode, can support a variety of RF bandwidth, that is, RF bandwidth can be Nx1.25mhz (N=1, 3, 5, 9 or 12). Currently, the technology supports only the first two, namely 1.25MHz (cdma2000-1x) and 3.75MHz (cdma2000-3x). Other technical features include: the more efficient use of wireless resources, the realization of a CDMA one to CDMA2000 system smooth transition; Core network protocol can use IS-41, Gsm-map and IP backbone network standard; forward transmit diversity; Fast forward power control; use turbo code ; auxiliary pilot channel; flexible frame length; reverse link coherent demodulation.

3.td-scdma

TD-SCDMA (Time division-synchronous Code Division multiple Access) is one of the technical standards for the third generation mobile communication space interface, which is officially released by the ITU. It has the full support of CWTS and 3GPP, China's telecommunications industry in the last hundred years to the first complete communication technology standards, is a CDMA, TDMA, FDMA technology advantages in one, large system capacity, high spectrum utilization, anti-interference ability of the mobile communication technology, using smart antennas, joint detection, Relay switching, synchronous CDMA, software radio, low bit rate, multi-slot, variable spread spectrum system, adaptive power adjustment and other technologies.

The technical features of TD-SCDMA are as follows: (1) spectrum flexibility and the ability to support cellular networks is high. TD-SCDMA requires only 1.6MHz of minimum bandwidth. If the bandwidth is 5MHz, 3 carriers are supported, the cellular network can be formed in one area, the mobile service is supported, and the asymmetric data service can be provided by automatic credit card channel allocation (DCA) technology. (2) High spectrum utilization. TD-SCDMA provides high spectral utilization for symmetric voice service and asymmetric data services. That is, TD-SCDMA can support one more user when using the same band width. (3) Low cost of equipment. In the antenna base station, TD-SCDMA equipment cost is low, mainly because (a) the smart antenna composed of multiple antenna array, coherent transceiver and DSP algorithm has the advantages of reducing multiple access interference, increasing capacity and receiving sensitivity, reducing transmitting power and antenna base station cost, etc. (b) Each terminal uplink signal is fully synchronized at the base station Demodulator, namely uplink synchronization, its advantage is the CDMA code channel orthogonal, reduces the code channel interference, enhances the CDMA capacity, may simplify the base station hardware, reduces the antenna base station cost, (c) realizes the radio function by the DSP software, namely the software radio technology, Can realize the smart antenna and multiuser detection, such as baseband digital signal processing, so that the system can flexibly use new technology, and can reduce product development cycle and cost. (4) System compatibility. Since TD-SCDMA also satisfies the requirements of IUB, A, Gb, Iu and Iur, the base station subsystem of TD-SCDMA can not only be used as the expansion of 2G and 2.5G GSM base station, but also can be used as the base station subsystem in 3G Network, which can take into account the current needs and future development.

Comparison of 4.3 kinds of technical standards

In 3 kinds of technical standard, WCDMA spread spectrum code rate is 3.84mchip/s, carrier bandwidth is 5mhz;cdma2000 spread spectrum code rate is 1.2288mchip/s, carrier bandwidth is 1.25MHz. In addition, WCDMA base-station synchronization is optional, and CDMA2000 synchronization is required, so the Global Positioning System (GPS) is required. The above two points is the most important difference between WCDMA and CDMA2000. TD-SCDMA spread-spectrum code rate is 1.28mchip/s, carrier bandwidth is 1.6MHz, the base station must be synchronized, compared with the other two technologies, using smart antenna, joint detection, uplink synchronization and dynamic channel allocation, relay switching and other technologies, with a flexible spectrum use, high frequency spectrum utilization, Suitable for asymmetric data services.

In addition, both WCDMA and CDMA2000 adopt the FDD mode, only TD-SCDMA adopts the TDD mode. FDD mode is characterized by the separation of two symmetrical frequency channels, the system to receive and send, the use of frequency bands to separate reception and transmission channels, the use of packet switching technology, can break through the bottleneck of the second generation of development, to achieve high-speed data services, and to improve the spectrum utilization, increase system capacity. But FDD must use a pair of frequencies, that is, to provide a third generation of service within each 2x5mhz bandwidth. This method can make full use of the spectrum of the upper and lower lines while supporting the symmetric service, but the spectrum utilization is greatly reduced when the asymmetric packet switching (Internet) is working, and the TDD model has FDD incomparable advantage.

The main problems faced by 5.3G system

The main problems faced by the third generation mobile communication systems are as follows: (1) multipath fading. This problem exists in all mobile communication systems. Radio waves in the process of transmission will be refraction, reflection and scattering, resulting in a number of propagation paths. When the signals of different paths reach the receiver, the amplitude and phase fluctuation of the receiving signal are different because of the position, direction and polarization of the antenna, which causes a serious decline phenomenon. In order to guarantee the quality of communication, it is necessary to increase the signal power, which directly affects the capacity of the system. (2) Delay extension. The signals of different paths have different propagation delay, then the interference between pulses is obvious when it extends over 10% of the pulse width, which limits the data rate of mobile communication. (3) Multiple access interference. Because the 3G system uses the CDMA technology, namely uses the different spread spectrum code word to differentiate the user, this request each user's spread spectrum code to have the strong autocorrelation and the weak correlation. But in fact, the mutual interference between the users can not completely disappear, so the CDMA system is the interference restricted system, that is, from the community and neighboring community users of interference into the decision system capacity and performance of the main factors. Multi-access jamming is a kind of interference peculiar to 3G system. (4) Near and far effect. When each mobile station is transmitting signal with same power, the signal power of the near Mobile station received by the base station will be much larger than the signal power emitted by the remote mobile station. The near-far effect refers to the strong interference from the nearby high-power signal to the remote small power signal. It is also a kind of multiple access interference, but in 3G system this kind of multiple access interference is very outstanding. (5) Institutional issues. At present, the second generation system has been widely used, so, from the perspective of resource utilization, 3G system must be compatible with the predecessor system, and in the future smooth transition to the fourth generation of mobile communication systems, and even the highest goal of personal communications systems. But at present, the second generation system is various, the standard is endless, the system is various. Therefore, how to make the 3G system to play a role in the past, but also a prominent problem.

6.3G Development Status

In terms of technical standards, WCDMA, CDMA2000 and TD-SCDMA these 3 technical standards have not reached maturity, all need to carry out comprehensive and in-depth research and testing, and test, any one of the standards in a certain area, a certain field has its advantages and specificity, therefore, 3 standards will be integrated, To complement each other, so as to improve and develop, and constantly towards maturity.

The commercialization of the third generation of mobile communications is entering the implementation phase in the global context. The North American Spring PCS, Bell Mobility, Verizon Wireless, KDDI in Japan and KT in Korea claim to have realized the commercialization of cdma2000-1x. In October 2001, the Japanese DoCoMo first achieved the commercialization of WCDMA. The relevant survey data show that location-related information on Demand business, multimedia SMS service, mobile internet Browsing Service, mobile E-commerce, interactive entertainment business will be the most promising future mobile communications business.