The growing need of mobile users to use the Internet from mobile devices is the main impetus for the emergence of networks, generation 2.5G, which became the transition between 2G and 3G. 2.5G networks use the same mobile communication standards as 2G networks, but support for packet data transmission technologies – GPRS (General Packet Radio Service), EDGE (Enhanced Data rates for GSM Evolution – increased transmission speed for GSM development) in GSM networks. The use of packet data transmission made it possible to increase the speed of information exchange when working with the Internet from mobile devices up to 384 kbps, instead of 9.6 kbps for 2G networks.
The HSCSD (High Speed Circuit Switched Data) system is the simplest upgrade of the GSM system designed for data transmission. The essence of this technology was to allocate not one, but several (theoretically up to eight) time slots to one subscriber. Thus, the maximum speed increased to 115.2 kbps. HSCSD provided a speed sufficient to access the Internet, however, during data transmission, data packets are separated by indefinite intervals, so the use of this technology is extremely wasteful. The fact is that HSCSD networks, like classical GSM networks, are based on circuit switching technology, in which a duplex channel is assigned to the subscriber for the entire duration of the communication session. Due to pauses in transmission, the channel resource was wasted irrationally.
The further evolution of the GSM system was the GPRS technology. Its implementation contributed to a more efficient use of the channel resource and the creation of a comfortable environment when working with the Internet. The GPRS system is designed as a packet data transmission system with a theoretical maximum transmission rate of about 170 kbit / s. The GPRS system is an extension of GSM networks with the provision of data services on the existing infrastructure, while the core network is expanding by overlaying new components and interfaces dedicated to packet transmission.
Progress did not stand still and, to increase the speed of data transmission, a new system was invented – EDGE. It provided for the introduction of a new modulation scheme. As a result, a speed of 384 kbps became achievable. EDGE has been introduced in GSM networks since 2003 by Cingular (now AT&T) in the United States.
GPRS and EDGE technologies have different names in different sources. They have already outgrown the second generation, but have not yet reached the third. GPRS was often called 2.5G, EDGE – 2.75G.
The main digital standards of second generation cellular communication systems:
D-AMPS (Digital AMPS – digital AMPS; 800 MHz and 1900 MHz bands);
CDMA (bands 800 and 1900 MHz);
JDC (Japanese Digital Cellular).
Third generation mobile communications (3G)
The further development of mobile networks was the transition to the third generation (3G). 3G is a standard for mobile digital communications, which under the abbreviation IMT-2000 (International Mobile Telecommunications 2000) unites five standards – W-CDMA, CDMA2000, TD-CDMA / TD-SCDMA, DECT (Digital Enhanced Cordless Telecommunication – advanced digital wireless communication technology). Of the listed 3G components, only the first three represent full-fledged third-generation cellular communication standards. DECT is a standard for wireless telephony for home or office use, which, within the framework of third generation mobile technologies, can only be used to organize hot spots (hotspots) to these networks.
With global satellite coverage, 3G networks must provide an exchange rate of at least 64 kbps. The basis of all third generation standards is code division multiple access protocols. This network access technology is not fundamentally new. The first work on this topic was published in the USSR back in 1935 by D.V. Agave.
Technically, code division networks operate as follows – each user is assigned a specific numeric code, which is distributed over the entire frequency band allocated for the network. In this case, there is no time division of signals, and the subscribers use the entire channel width. In this case, of course, the signals of the subscribers are superimposed on each other, but thanks to the numeric code they can be easily differentiated. As mentioned above, this technology has been known for a long time, but until the mid-80s of the last century it was classified and was used exclusively by the military and special services. After the removal of the secrecy labels, its active use began in civilian communication systems.