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Development of Mobile Communications

The modern mobile communication has experienced two generations and evolved into the third generation (3G). The first generation is the analog cellular mobile communication network in the time period from the middle of 1970s to the middle of 1980s. 

The most important breakthrough in this period is the concept of cellular networks put forward by the Bell Labs in the 1970s, as compared to the former mobile communication systems. The cellular network system is based on cells to implement frequency reuse and thus greatly enhances the system capacity. The typical examples of the first generation mobile communication systems are the AMPS (Advanced Mobile Phone System) and the later enhanced TACS (Total Access Communication System) of USA. The main feature of the first generation mobile communication systems is that they use the frequency reuse technology, adopt analog modulation for voice signals and provide an analog subscriber channel every other 30 kHz/25 kHz. However, their defects are also obvious
Low utilization of the frequency spectrum
Limited types of services
No high-speed data services
Poor confidentiality and high vulnerability to interception and number embezzlement
High equipment cost
Large volume and big weight

To solve these fundamental technical defects of the analog systems, the digital mobile communication technologies emerged and the second generation mobile communication systems represented by GSM and IS-95 came into being in the middle of 1980s. The typical examples of the second generation cellular mobile communication systems are the DAMPS (Digital Advanced Mobile Phone System) of USA, the IS-95 and the European GSM system. The GSM (Global System for Mobile Communications) is originated from Europe. Designed as the TDMA standard for mobile digital cellular communications, it supports the 64 kbps data rate and can interconnect with the ISDN. It uses the 900 MHz band while the DCS1800 system uses the 1800 MHz band. The GSM system uses the FDD and TDMA modes and each carrier supports eight channels with the signal bandwidth of 200 kHz. The DAMPS is also called the IS-54 (North America Digital Cellular System). Using the 800 MHz bandwidth, it is the earlier of the two North America digital cellular standards and specifies the use of the TDMA mode. The IS-95 standard is another digital cellular standard of North America. Using the 800 MHz or 1900 MHz band, it specifies the use of the CDMA (Code Division Multiple Access) mode and has already become the first choice among the technologies of American PCS (Personal Communication System) networks.

Since the 2G mobile communication systems focus on the transmission of voice and low-speed data services, the 2.5G mobile communication systems emerged in 1996 to address the medium-rate data transmission needs. These systems include GPRS ( General Packet Radio Service ) and IS-95B. The CDMA system has a very large capacity that is equivalent to ten or even twenty times that of the analog systems. It also has good compatibility with the analog systems. Currently some countries and regions such as USA, Korea and Hong Kong have put the CDMA system into operation to provide services for subscribers. As the narrowband CDMA technologies come into maturity at a time later than the GSM technologies, their application far lags behind the GSM ones and currently they have only found large-scale commercial applications in North America, Korea and China. The major services of mobile communications are currently still voice services and low-speed data services. With the development of networks, data and multimedia communications have also witnessed rapid development; therefore, the target of the 3G mobile communication is to implement broadband multimedia communication.

The 3G mobile communication systems are a kind of communication system that can provide multiple kinds of high quality multimedia services and implement global seamless coverage and global roaming. They are compatible with the fixed networks and can implement any kind of communication at any time and any place with portable terminals. The major systems include WCDMA, cdma2000 and TD-SCDMA

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