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First of all, there are two most commonly used systems in the world, namely GSM and CDMA. China Mobile is a company specializing in GSM, and China Unicom is mainly engaged in CDMA. In addition, they run GSM concurrently, so compared with mobile, GSM is not mature, and the business is not as much as mobile, but they seem to do well in CDMA. GSM and CDMA use different working principles and need professional knowledge. In short, their two systems are the most mature in the world. The former adopts continuous wave and the latter adopts pulse wave. Therefore, GSM will have an impact on some digital devices, but it does not mean that the radiation is greater than CDMA, but it is actually the same.

GPRS is a wireless general packet technology based on GSM network. At present, only Mobile does this business in China, which is an upgrade of the second generation communication technology. So people call GPRS the second generation communication technology. Now there is 3G, which is an upgrade of the second generation. The main advantages of GPRS are mobility, convenience, speed and security. As long as there is a signal, you can connect to the network through GPRS (if the mobile phone supports it, you can also connect to the Internet), which is charged according to the flow, so it has nothing to do with the time. Mainly used for surfing the Internet and downloading programs on mobile phones. At present, GSM is frequently used in most parts of the world because it is very mature.

CDMA was originally developed by the United States for military use, and later used for civilian use. It is characterized by good confidentiality, anti-interference, good call quality and high transmission efficiency, and can transmit multiple signals at the same time. CDMA is used in Korea.

In addition, CDMA is the abbreviation of code division multiple access, which translates to code division multiple access. This is a technology used to realize channel sharing in modern communication technology.

The so-called channel can be a specific frequency region of electromagnetic signal, called frequency band; It can also be a specific time period of the signal, called a frame. The so-called channel sharing means that multiple users use the same channel at the same time and ensure that they do not interfere with each other. Channel sharing can improve the utilization rate of channel resources.

There are many different technologies that can be used to realize channel enjoyment. The channel frequency band is divided into several narrow disjoint frequency bands (called subbands), and each subband is assigned to a user (called an address). This technology is called "frequency division multiple access" technology, which is FDMA (frequency division multiple access/address) in English. This is the basic technology of analog carrier communication, microwave communication and satellite communication, and it is also the basic technology of the first generation of analog mobile communication. Similarly, a channel frame can be divided into several non-overlapping time slots, and each time slot can be assigned to a user as a dedicated address. This is time division multiple access (TDMA). This is the basic technology of digital data communication and the second generation mobile communication. If each user's address is neither a designated signal subband nor a time slot, but a set of orthogonal coding structures (codes) of signals, then these user signals can also be transmitted on the same channel at the same time without interfering with each other. This technology is called "code division multiple access", which is CDMA.

Theory and practice have proved that compared with FDMA and TD-MA, CDMA has higher channel resource utilization rate under the same channel conditions, so it has become the basic mode of the third generation mobile communication channel.

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First, the development history of GSM digital mobile communication

Historical background of 1. 1 GSM system

GSM digital mobile communication system is designed by standardization committee composed of major European telecom operators and manufacturers, and it is developed on the basis of cellular system.

The concept and theory of cellular system were put forward by Bell Laboratories in 1960s, but its complex control system, especially the control of mobile station, did not provide the technical basis for the realization of cellular mobile communication until 1970s with the maturity of semiconductor technology, the development of large-scale integrated circuit devices and microprocessor technology and the wide application of surface mount technology. Until 1979, the United States opened the first AMPS (Advanced mobile telephone service) analog cellular system in Chicago, while Northern Europe also opened the NMT (Nordic Mobile Phone) system in Sweden in September of 198 1 year, and then Europe successively opened the TACS system in Britain and the C-450 system in Germany.

The emergence of cellular mobile communication can be said to be a revolution in mobile communication. Its frequency reuse greatly improves the frequency utilization rate and increases the system capacity. Intelligent network has realized the functions of switching and roaming, and expanded the service scope of customers. However, the above simulation system has four main disadvantages:

There is no common interface between 1. systems;

2. It is difficult to carry out data bearing services;

3. The spectrum utilization rate is low, which can't meet the demand of large capacity;

4. Poor security, easy to be eavesdropped and easy to become a "fake machine". Especially in Europe, there is no common interface between systems, so it is impossible to roam with each other, which has caused great inconvenience to customers.

GSM digital mobile communication system originated in Europe. As early as 1982, several analog cellular mobile systems have been running in Europe, such as NMT (Nordic Mobile Phone) in many Nordic countries and TACS (Total Access Communication System) in Britain, and other western European countries also provide mobile services. At that time, these systems were all domestic and could not be used abroad. In order to facilitate the unified use of mobile phones in Europe, a public system is needed. 1982, Nordic countries submitted a proposal to CEPT (European University of Posts and Telecommunications Administration), requesting to formulate a public * * European telecommunications service specification in 900MHz band. At this conference, the "Group SpecialMobile" was established under the Technical Committee of the European Telecommunications Standards Institute (ETSI) to formulate relevant standards and proposals.

65438-0986 In Paris, the team conducted field experiments on eight suggestion systems proposed by European countries and companies after a lot of research and experiments.

1987 in may, GSM member countries reached an agreement on adopting narrowband TDMA, RPE-LTP speech coding excited by regular pulses and GMSK modulation of Gaussian filter minimum shift keying. In the same year, the operators and managers of Europe 17 countries signed a Memorandum of Understanding (MoU) and reached an agreement to fulfill the specifications. At the same time, the MoU organization was established and devoted to the development of GSM standards.

The specification of GSM900 was completed in 1990, and about 130 comprehensive proposals were produced. Different suggestions are grouped into a set of 12 series.

The first system was launched in Europe on 199 1. At the same time, Mou Organization designed and registered the market trademark for the system, and renamed GSM as "Globa 1 Mobile Communication System". Since then, mobile communication has entered the second generation digital mobile communication system. In the same year, the mobile task force also completed the formulation of the public * * * European telecom service specification in 1800MHz band, named DCSI800 system. The system has the same basic functional characteristics as GSM900, so this specification only accounts for a small part of GSM recommendation. Only the differences between GSM900 and DCSI800 are described, and most of them are universal. Both systems can be called GSM systems.

1992 most European GSM operators have started commercial services. By May, 1994, there were 50 GSM networks in operation all over the world. /kloc-in June of 0/0, the total number of customers has exceeded 4 million, and international roaming customers make more than 5 million calls every month, with an average increase of over 50%.

1993 the first DCSI800 system in Europe was put into production. Up to 1994, six operators have adopted the system.

1.2 GSM system technical specification

In the technical specification of GSM system, only the functions and interfaces are specified in detail, but the hardware is not specified. The purpose of this is to minimize the restrictions on designers and enable operators to purchase equipment from different manufacturers.

The technical specification of GSM system is divided into 12 chapters:

Overview of 0 1 series

02 business aspects

03 network aspect

04 MS-BS interface and protocol

Physical layer on wireless path

06 speech coding specification

Terminal adapter for 07 milliseconds

08 base station-mobile switching center interface

09 network interconnection

10 business interchange

1 1 equipment and model approval specification

12 operation and maintenance

These series of specifications were compiled by different working groups and expert groups established by ETSI. The first edition of the first-stage standard was completed in the spring of 1988 to support the bidding activities at that time. It was revised several times later. After 1990, except for the fax specification, there are few other changes, which are basically frozen at the end of 1992. The second phase standard basically completed the main part by the end of 1993, and was frozen by the end of 1994. In order to improve the performance of the system, the definition of the second-stage standard was reconsidered from 1994, and then it was incorporated into the second-stage standard, and it was announced that there would be a third-stage standard. In fact, due to the proposal of the third generation mobile communication system, the third-stage standard has been suspended.

In order to ensure the existing and future services in GSM network, compatibility requirements must be considered when formulating standards.

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GPRS- General Packet Radio Service is a wireless packet switching technology based on GSM system, which provides end-to-end and wide-area wireless IP connection. Generally speaking, GPRS is a high-speed data processing technology, and the method is to transmit data to users in the form of "packets". Although GPRS is a transitional technology from the existing GSM network to the third generation mobile communication, it has obvious advantages in many aspects. At present, Hong Kong, as the first area to conduct GPRS field test, has achieved good results.

Because of the use of "grouping" technology, users can avoid the pain of disconnection when surfing the internet (the situation is probably similar to using the download software NetAnts). In addition, the method of accessing the Internet using GPRS is different from WAP. Using WAP to surf the Internet is like surfing the Internet at home. After surfing the Internet, you can't use the telephone line at the same time, but GPRS is superior. You can download data and talk at the same time. Technically speaking, GSM will continue to be used for voice transmission (that is, call), while GPRS can be used for data transmission. In this way, the application of mobile phones will be promoted to a higher level. Moreover, the development of GPRS technology is also very "economical", because it can only be developed according to the existing GSM network. GPRS is widely used, including sending and receiving e-mails through mobile phones and surfing the Internet.

At present, the slogan of mobile Internet access is "always online" and "IP in hand". After using GPRS, data can be sent and received in groups, which means that users are always online and charged according to the flow, which quickly reduces the service cost. For the WAP tariff policy of China Mobile/China Unicom, which is still difficult to produce at present, if the CSD (circuit switched data, commonly known as dial-up data) bearer is changed to GPRS, it means that dozens of people will bear the original cost.

The biggest advantage of GPRS is that the data transmission speed is not as fast as WAP. At present, the transmission speed of GSM mobile communication network is 9.6kbytes per second, and the transmission speed of GPRS mobile phone has reached 9.6Kbps when it was launched at the beginning of this year, and now it has reached 1 15Kbps (twice the ideal speed of the commonly used 56Kmodem).