Читать книгу Spatial Multidimensional Cooperative Transmission Theories And Key Technologies - Lin Bai - Страница 14

The concept of the third-generation mobile communication system was proposed by the ITU in 1985 and it was named the future public land mobile telecommunications system (FPLMTS). In 1996, it was renamed the international mobile telecommunications 2000 (IMT-2000) system, which worked in the 2000-MHz band and could provide a data transmission rate of up to 2000 kbit/s. The purpose of 3G is to achieve a unified standard for cellular mobile communication and establish a globally popular seamless roaming system. Meanwhile, it can support high-quality multimedia services and enhance network capacity and multiple-user management capabilities. Therefore, IMT-2000s requirements for 3G technology are as follows: (1) high data transmission rate including the minimum rate of satellite link 9.6 kbit/s, indoor environment at least 2 Mbit/s, outdoor walking and vehicle environment at least 384 kbit/s and 144 kbit/s, respectively, (2) transmission rate allocation on demand, (3) uplink and downlink adapting to the needs of asymmetric services, (4) simple cell structure and easy-to-manage channel structure, (5) flexible frequency and radio resource management, system configuration, and service facilities, and (6) the combination of wireless network and wired network, trying to achieve the same transmission quality as that of the wired network.

On October 19, 2007, the ITU officially approved the IEEE 802.16-based worldwide interoperability for microwave access (WiMax) to become the 3G standard. WCDMA and cdma2000 have been commercialized on a global scale, and China also began commercialization based on TD-SCDMA 3G system in 2008. However, 3G has its limitations which are as follows: (1) Using CDMA it is difficult to achieve high communication rate due to multi-user interference, (2) due to the limitation of the air interface to the core network, the dynamic range of service rates provided by 3G is not large enough to meet various service types, (3) the frequency resources allocated to 3G have become saturated, (4) the voice switching architecture adopted by 3G still inherits 2G circuit switching rather than pure IP, and (5) the applications of streaming media are not satisfactory. Therefore, more advanced technologies are needed to further improve the quality of mobile services.