The Global System for Mobile Communications, known as GSM, is the most widely used mobile phone standard at present. More than 6,543.8 billion people in more than 200 countries and regions around the world are using GSM mobile phones. The ubiquity of GSM standard makes it common for users to roam internationally after signing a "roaming agreement" between mobile phone operators. The biggest difference between GSM and previous standards is that its signaling and voice channels are digital, so GSM is regarded as the second generation (2G) mobile phone system. This shows that digital communication has been established in the system for a long time. GSM is an open standard currently developed by 3GPP.
20 15 years, many GSM network operators around the world have determined 20 17 years as the year to close the GSM network.
Chinese name: global mobile communication system MBTH: global system for mobile communications English abbreviation: GSM application: mobile phone development, development history, specific introduction, mobile communication technology, wireless interface, frequency configuration, GSM900MHz band, China GSM 900 frequency, DCS 1800MHz band, China DCS 1800 frequency, market situation, system structure, security level, technical features, intuitive features of GSM use, and its main technical features are as follows: Unit of measurement, development situation GSM is the most extensive, and more than 6,543.8 billion people in more than 200 countries and regions around the world are using GSM mobile phones. All users can roam freely between mobile phone operators who have signed roaming agreements. The biggest difference between GSM and previous standards is that its signaling and voice channels are digital, so GSM is regarded as the second generation (2G) mobile phone system. This shows that digital communication has been established in the system for a long time. GSM is an open standard currently developed by 3GPP. From the user's point of view, the main advantage of GSM is that users can choose between higher digital voice quality and low-cost short messages. The advantage of network operators is that they can customize their own equipment configuration according to different customers, because GSM0 as an open standard provides easier interoperability. In this way, the standard allows network operators to provide roaming services and users can use their mobile phones all over the world. As a developing standard, GSM is still backward compatible with the original GSM phone. For example, the message exchange capability is added to the release' 97 version of the standard, namely GPRS. In the Release'99 standard, high-speed data exchange is also introduced, mainly EDGE and UMTS standards. Development history Although GSM has been quite popular at present, the history of conceiving mobile phones began long before GSM. GSM group ("Groupe Spécial Mobile" (French) 1, 2, 3, 4) was founded in 1982. The name of GSM also comes from the name of this group, although it was later decided to replace its original intention with abbreviation. Initially, this group was managed by CEPT. The original technology of GSM system is defined in 1987. ETSI succeeded CEPT. 1990 the first GSM specification was completed, and the text of this specification is more than 6000 pages long. 199 1 started commercial operation in Radiolinja, Finland. 199 1 year, the first GSM system was opened in Europe, and the mobile operators designed and registered a trademark that met the market requirements, and renamed GSM as Global System for Mobile Communications (GSM). Although GSM is the second generation mobile communication technology standard originated in Europe, its original intention of research and development is to let the world use the same mobile phone network standard, so that users can travel around the world with one mobile phone. GSM is also the origin of the name "GSM", which is a famous mobile service brand in China. 1992 european committee for standardization unified standard adopts digital communication technology and unified network standard, which can ensure communication quality and develop more new services for users. The transmission speed of GSM mobile communication network is 9.6k/s, and the global number of GSM mobile users has exceeded 65.438+0 billion, covering 654.38+0/7 of the population. The proportion of GSM technology in the world digital mobile phone field has exceeded 70%. Because GSM is the second generation mobile communication technology compared with analog mobile communication technology, it is called 2G for short. Because of the openness of the GSM standard, the frequency utilization rate is higher than that of the analog network (about 1.8-2 times of that of the analog network), and it is rapidly popularized all over the world, becoming the dominant technology of the digital mobile communication (also known as the second generation) network. The difference between GSM mobile phone and "big brick" analog mobile phone lies in the addition of subscriber identity card (SIM card)-mobile station (mobile phone) without SIM card can't access the network. Once the GSM network recognizes the identity of users, it can provide various services. 1998, 3G cooperation project (3GPP) started. Initially, the goal of this project was to formulate detailed specifications for the next generation mobile communication network (3G). However, 3GPP has also accepted the work of maintaining and developing GSM specifications. ETSI is a member of 3GPP. 20 15 years, many GSM network operators around the world have determined 20 17 years as the year to close the GSM network. The reason for shutting down GSM and other 2G networks is to release radio frequency resources for building 4G and future 5G networks. The mobile communication technology GSM belongs to the second generation (2G) cellular mobile communication technology. Analog cellular technology is called the first generation mobile communication technology, and broadband CDMA technology is called the third generation mobile communication technology, namely 3G. The radio interface GSM is a cellular network, which means that the mobile phone should be connected to the nearest cell area that it can search. GSM networks work on several different radio frequencies. GSM network has four different cell sizes: mega cell, micro cell, picocell and umbrella cell. The coverage varies according to the environment. Giant cell can be regarded as the kind where the base station antenna is installed on the mast or the roof. Micro-cells are those whose antenna height is lower than the average building height and are generally used in urban areas. Micro-cell is a kind of small cell with a coverage of only tens of meters, which is mainly used indoors. Umbrella cell is used to cover the blind area of small cellular network and fill the signal blank area between cells. According to the antenna height, gain and propagation conditions, the radius of the honeycomb can range from more than 100 meters to dozens of kilometers. The actual longest distance GSM specification supports 35 kilometers. There is also a concept of expanding the hive, and the radius of the hive can be doubled or even more. GSM also supports indoor coverage, and the power of outdoor antenna can be distributed to indoor antenna distribution system through power distributor. This is a typical configuration scheme to meet the requirements of indoor high-density calls, which is very common in shopping centers and airports. But this is not necessary, because indoor coverage can also be achieved by wireless signals passing through buildings, but this can improve signal quality and reduce interference and echo. Frequency configuration GSM 900MHz band GSM 900MHz band duplex interval is 45MHz, effective bandwidth is 25MHz, 124 carrier frequencies, and each carrier frequency has 8 channels. GSM900: uplink (MHz) 890-915; Downlink (MHz) 935-960 (the first frequency band realized by GSM and the most widely used frequency band) GSM900E: uplink (MHz) 880-915; Downlink (MHz)925-960(900MHz extended band) China GSM900 using frequency ① China Mobile● Uplink band: 890-909 MHz ● Downlink band: 935-954 Mhz ② China Unicom ● Uplink band: 909-9 15 MHz ● Downlink band: 954-960 MHz DCS 6544 GSM 1800MHz band, duplex interval of 95MHz, effective bandwidth of 75MHz, 374 carrier frequencies, each with 8 channels. GSM 1800: uplink (MHz)1710-1785; Downlink (MHz) 1805- 1880 (applicable to the market with large demand for channel capacity, and its application scope is second only to 900M). China DCS 1800 frequency ① China Mobile ● Uplink band:171720mhz ● Downlink band:1805-1815mhz ② China Unicom. Market situation of 5438+0840- 1850 MHz By 2004, more than 10 billion people in the world used GSM mobile phones, accounting for 70% of the global mobile phone market. CDMA, the main competitor of GSM (mainly used in the United States and Canada), has a good prospect, but it has limitations. As the transition of 3G standard, CDMA has not shown all its functions. Also, because of the delay in the construction of W-CDMA network, at least in the high-density call market, GSM will gradually die out, but it will be a matter of time. The increase of GSM users between 1998 and 2000 is mainly due to the introduction of prepaid telephone service by mobile operators. It allows people who can't or don't want to sign a contract with an operator to own a mobile phone. Competition among European mobile operators is also fierce. Even without a long-term visa, people can buy a mobile phone from the operator at a very low price. System structure GSM system is mainly composed of four parts: mobile station (MS), mobile network subsystem (NSS), base station subsystem (BSS) and operation and maintenance center (OMC). Figure 1 GSM system structure The mobile station (MS) is the equipment used by users in the public GSM mobile communication network, and it is also the only equipment that users can directly contact in the whole GSM system. The types of mobile tables include not only hand-held tables, but also car-mounted tables and portable tables. With the development trend of GSM standard digital handheld station to miniaturization, lightweight and multifunction, the users of handheld stations will account for a large part of the whole users. Base Station Subsystem (BSS) Base Station Subsystem (BSS) is the most direct and basic component of GSM system. It is directly connected with the mobile station through the wireless interface, and is responsible for wireless transmission and reception and wireless resource management. On the other hand, the base station subsystem is connected with the Mobile Service Switching Center (MSC) in the network subsystem (NSS) to realize the communication connection between mobile users or between mobile users and fixed network users, and transmit system signals and user information. Of course, in order to manage the operation and maintenance of BSS, it is necessary to establish a communication line between BSS and OSS. Mobile Network Subsystem (NSS) The mobile network subsystem (NSS) mainly includes the switching function of GSM system and the database function required for user data, mobility management and security management. It plays a management role in the communication between GSM mobile users and between GSM mobile users and users of other communication networks. NSS is composed of a series of functional entities. The whole GSM system, that is, between functional entities of NSS and between NSS and BSS, communicates with each other through the No.7 signaling network conforming to CCITT signaling system protocol and GSM specification. Operation and Maintenance Center (OMC) Operation and Maintenance Center (OMC), also known as OSS or M2000, needs to complete many tasks, including mobile user management, mobile device management and network operation and maintenance. Security level GSM is designed to have a medium security level. System design uses * * * to enjoy key user authentication. Communication between users and base stations can be encrypted. The development of UMTS provides an option, namely USIM, which uses a longer authentication key to ensure better security and two-way authentication between the network and users. GSM only has network-to-user authentication. Although the security module provides confidentiality and authentication functions, the authentication ability is limited and can be forged. GSM uses a variety of secure encryption algorithms. A5/ 1 and A5/2 stream ciphers are used to ensure the confidentiality of voice over the air. A5/ 1 is a strong algorithm used in Europe, and A5/2 is a weak algorithm used in other countries. In these two algorithms, serious loopholes have been found. For example, a single ciphertext attack may interrupt A5/2 in real time. However, the system supports many different algorithms, so operators can switch to a stronger security level. Technical features The intuitive features of GSM in use: The GSM system has several important features: good anti-theft copying ability, large network capacity, rich mobile phone number resources, clear call, strong stability, not easy to be disturbed, sensitive information, few dead angles in call, low power consumption of mobile phones, and separation of machine and card. Its main technical features are as follows: 1. Spectrum efficiency. The system has high spectral efficiency because of the efficient modulator, channel coding, interleaving, equalization and speech coding technologies. 2. Capacity. Due to the increase of transmission bandwidth of each channel, the interference ratio of co-frequency multiplexing is reduced to 9dB, so the co-frequency multiplexing mode of GSM system can be reduced to 4/ 12 or 3/9 or even less (7/2 1 for analog system). Coupled with the introduction of half-rate speech coding and automatic service allocation to reduce the number of handovers, the capacity efficiency of GSM system (the number of channels per megahertz per cell) is 3 ~ 5 times higher than that of TACS system. 3. Voice quality. In view of the characteristics of digital transmission technology and the definitions of air interface and voice coding in GSM specification, the voice quality always reaches the same level above the threshold regardless of the wireless transmission quality. 4. Open interface. The open interface provided by GSM standard is not limited to air interface, but also includes interfaces between networks and between equipment entities in the network, such as A interface and Abis interface. 5. Safety. Through authentication, encryption and the use of TMSI numbers, the purpose of security is achieved. Authentication is used to verify users' network access rights. The air interface uses encryption, which is determined by the key of SIM card and network AUC. TMSI is a temporary identification number assigned to users by commercial networks to prevent people from tracking and exposing their geographical location. 6. interconnection with ISDN and PSTN. Interconnections with other networks usually use existing interfaces, such as ISUP or TUP. 7. roaming based on SIM card. Roaming is an important feature of mobile communication, which means that users can automatically enter another network from one network. GSM system can provide global roaming, and of course it also needs some protocols between network operators, such as billing. The unit of measurement GSM is the unit of measurement of PP products, and its name is "gram weight". Used to indicate the strength of PP woven products. The larger the value, the better the product quality. It is a comprehensive record of tear resistance, puncture resistance and tensile strength. G * * * = weight per square meter (gram)