GSM system has several important features: good anti-theft ability, large network capacity, rich mobile phone number resources, clear call, strong stability, sensitive information, few dead ends and low power consumption of mobile phones.
At present, the two main GSM standards in China are GSM900 and GSM 1800. Because the frequencies used are different, the applicable mobile phones are different. But at present, most mobile phones are basically dual-band mobile phones, which can be switched freely between these two frequency bands. In addition to GSM900 and GSM 1800, GSM 1900 has been added to the systems widely used in European countries, and the mobile phone is a tri-band mobile phone. With the further development of China's mobile phone market, there are also three-band mobile phones, that is, mobile phones that can switch freely in the three frequency bands of GSM 900 \ GSM1800 \ GSM1900, which truly realizes that a mobile phone can travel all over the world.
The early GSM900 developed earlier and was used more, while GSM 1800 developed later. In terms of physical characteristics, the former has low frequency spectrum, long wavelength and poor penetration, but the transmission distance is long, while the mobile phone has strong transmission power, large power consumption and short standby time; The latter has higher frequency spectrum, shorter wavelength and better penetration, but its transmission distance is short, its mobile phone transmission power is small and its standby time is correspondingly long.
Code Division Multiple Access (code division multiple access)
CDMA (Code Division Multiple Access) is translated into "Code Division Multiple Access Packet Data Transmission Technology", which is called the second and fifth generation mobile communication technologies. At present, the markets adopting this technology are mainly in the United States, Japan and South Korea. CDMA mobile phone is called "green mobile phone" because of its clear voice, low transmission power and strong confidentiality. The transmission power is only 1/60 of that of GSM mobile phone. More importantly, CDMA based on broadband technology makes video application possible in mobile communication.
The principle of CDMA technology is based on spread spectrum technology, that is, the information data to be transmitted with a certain signal bandwidth is modulated by a high-speed pseudo-random code with a bandwidth much larger than the signal bandwidth, so that the bandwidth of the original data signal is expanded and then transmitted by carrier modulation. The receiver uses the same pseudo-random code to correlate with the received bandwidth signal, and changes the broadband signal into the narrowband signal of the original information data, that is, despreading, thus realizing information communication.
The advantages of CDMA include:
The speech coding technology provided by CDMA can reduce the noise of the surrounding environment and make the call clearer.
CDMA adopts spread spectrum communication technology, so it can reduce the interference between mobile phones and increase the capacity of users. Moreover, the power of the mobile phone is relatively low, which can not only increase the use time, but also reduce the electromagnetic wave radiation and reduce the harm to people to a certain extent.
The bandwidth of CDMA can be greatly expanded, and images can also be transmitted.
As far as security performance is concerned, CDMA has a good authentication system, and because of its transmission characteristics, it greatly enhances the ability to prevent eavesdropping.
third generation
G stands for English 3rdGeneration, and stands for the third generation mobile communication technology. Mobile phones have experienced the first generation of analog mobile phones (1G) and the second generation of digital mobile phones (2G) such as GSM and TDMA. At present, 3G advocated by communication operators and terminal product manufacturers refers to a new generation of mobile communication system that combines wireless communication with multimedia communication such as the Internet. It can handle various media forms, such as images, voice and video streams, and provide various information services, including web browsing, teleconference and e-commerce. Provide strong support for the integration of mobile phones into multimedia elements.
The main targets of the third generation communication network are real-time video, high-speed multimedia and mobile Internet access services. The above services can be realized by using advanced air interface technology, core packet technology and efficient use of spectrum. Although high-speed data transmission capability is one of the key features of the third generation wireless network, its real advantage is to expand the capacity of high-quality voice services. At present, the expansion speed of high-quality voice service capacity supported by the second generation network can no longer meet the growth of customer demand. High data capacity can bring mobile users closer to the Internet. In addition to increasing technical complexity, network communication based on ATM or IP technology will greatly reduce the cost of voice and data services.
3G technical standards: As early as May 2000, the International Telecommunication Union (ITU) determined three mainstream 3G standards: W-CDMA, CDMA2000 and TD-SCDMA.
W-CDMA: WidebandCDMA, which means wideband code division multiple access, is a 3G technical specification developed from GSM network. Its supporters are mainly European manufacturers based on GSM system, including Ericsson, Nokia, Lucent, Nortel and NTT, and Fujitsu and Sharp in Japan. This system can be set up on the existing GSM network to facilitate the transition of system providers, and Asia, where GSM system is quite popular, will have a higher acceptance of this new technology. Therefore, W-CDMA has inherent market advantages. At present, there are many W-CDMA mobile phone products, but there is no perfect 3G network in China.
CDMA2000: It was put forward by Qualcomm North America Company of the United States, and Motorola, Lucent and Samsung of South Korea all participated. At present, South Korea is the leader of this standard. This standard originated from narrow-band CDMA2000 1X digital standard, which can be directly upgraded from the original CDMA2000 1X structure to CDMA20003X(3G) with low construction cost. But at present, only Japan, South Korea and North America use CDMA, and China Unicom has also applied this mode transition. CDMA2000 has fewer supporters than W-CDMA. However, the research and development technology of CDMA2000 is the fastest among the current standards, and many 3G mobile phones are ahead.
TD-SCDMA: The full name is TimeDivision-SynchronousCDMA, which is a 3G standard proposed by China Datang Telecom Company. The standard integrates international leading technologies such as intelligent wireless, synchronous CDMA and software radio. Due to the huge domestic market in China, the standard has attracted the attention of major telecom equipment manufacturers. More than half of the equipment manufacturers in the world have announced that they can support TD-SCDMA standard, which is a great opportunity for China's communication industry.
Because 3G commercialization needs a huge project, involving many complicated levels, it is impossible to connect from the current 2G to 3G at once, so 2.5G mobile phones came into being. At present, the commercial 2.5G mobile communication technology can be regarded as the connection technology from 2G to 3G, and technologies such as HSCSD, WAP, EDGE, Bluetoot and EPOC are all 2.5G technologies.