New GSM technologies for security personnel. GSM history.

Data transmission via traffic channels (speed up to 9600 bit/s) or short message services (short data arrays up to 1120 bits long) in combination with satellite radio navigation equipment makes it possible to build systems for tracking especially important cargo, dispatching systems for special vehicles, car security systems and systems for searching for stolen cars.

However, new technologies for high-speed data transmission via GSM channels allow security services to implement fundamentally new opportunities.

The GPRS radio interface packet transmission technology(General Packet Radio Service) presented at the recent Svyaz-Expocomm 2000 exhibition by Mobile TeleSystems (MTS)), which is expected to be implemented in Moscow this year, will significantly increase the speed of data transfer.

The company «VimpelCom» is also planning to deploy the GPRS infrastructure. It has signed an agreement with Nokia to supply elements of the GSM infrastructure for the Beeline GSM cellular network deployed in Moscow.

The main tasks of GPRS are to provide mobile Internet access services, support for intranets, and other IP applications.

GPRS implementation requires the installation or overlay on the GSM network infrastructure of new elements that enable data packet switching.

The basic architecture of the GSM network with GPRS functions is shown in Fig. 1.

BTS (Base Transceiver Station) — base transceiver station;
BSC (Base Station Controller ) — base station controller;
MSC(Mobile Switching Centre) — mobile service switching centre;
SGSN(Serving GPRS Support Node) — GPRS service node;
GGSN(Gateway GPRS Support Node) — GPRS gateway node;
PCU(Packet Controller Unit) — packet controller;
OMC-G(Operating & Maintenance-GPRS) — GPRS service centre

Fig. 1. Basic GPRS architecture

As is known, the GSM standard uses time-division multiple access (TDMA).

The structure of the digital information flow is built on the basis of so-called TDMA frames, each of which consists of 8 time positions (slots). In each of the time slots, information from its channel is transmitted: speech or data.

In the GSM network with GPRS, time slots are combined to increase the transmission speed. From 1 to 7 slots are allocated for data transmission, theoretically – 8.

In GPRS mode, a slot can be formed using four error-correcting coding schemes (CS-1 … CS-4), which differ in the transmission and coding speed, as well as the level of error protection.

The lower the coding speed, the higher the level of error protection (Table 1).

Table 1.

Thus, when using all 8 time slots and the highest coding rate (without error protection), the data transfer rate in GPRS mode can be 21.4 x 8 = 171.2 kbps.

However, in practice, one can expect data transfer rates of up to 100 kbps, which, nevertheless, exceeds the capabilities of existing GSM networks by an order of magnitude.

A further increase in data transfer rates can be achieved using EDGE (Enhanced Data Rates for GSM) technology. The essence of this technology is the use of 8-position phase shift keying 8PSK in the radio channel instead of GMSK modulation.

Due to this, it is possible to transmit 3 information bits per symbol, i.e. a threefold increase in the transmission speed. The use of EDGE provides a data transmission speed on the radio interface of up to 384 kbit/s.

It should be noted that such high data transmission speeds cannot be achieved in conventional and trunking systems existing in Russia.

Even in the promising pan-European standard of trunking radio communication TETRA, where the maximum data transfer rate is achieved in comparison with other standards, it cannot exceed 28.8 kbit/s. In addition, the existing territorial coverage of cellular communication after the implementation of the considered technologies will allow information to be transmitted over significant distances, which are also unlikely to be achievable in professional radio communication networks.

Increasing the data transfer rate in cellular networks makes it possible for a mobile subscriber to receive large amounts of data in a relatively short time.

Along with access to open information systems (Internet access, etc.), security service employees will be able to organize quick receipt of information from their own specialized databases (identify the owner of a car, obtain an installation on a surveillance object, etc.).

It becomes possible to quickly transmit images via radio channels. The information speed in GSM networks with the introduction of new technologies does not yet allow the transmission of video information in real time, but the rapid transmission of photographs is absolutely real.

Law enforcement agencies and security services have an accessible communication channel for transmitting photographs from the scene.

For example, technical means of transmitting data using GPRS technology can be included in the composition of mobile robotic complexes used during special events. (See Batanov A.F., Gritsynin S.N., Murkin S.V. “Robotic systems for supporting special operations”, “Special equipment”, No. 6, 1999).

Thus, , when carrying out work to defuse explosive devices, in difficult situations, an image of an explosive device can be quickly transmitted to a monitor by a group of experts who are not directly at the scene of the event, in order to make a decision on defusing methods.

High-speed data transmission technologies via GSM channels can in principle be used in video surveillance systems, when the control post must be set up at a fairly large distance from the object being monitored. In this case, naturally, not a continuous video image will be transmitted, but fixed video frames with a certain periodicity.

Dedicated networks

Mobile operators are trying in every way to increase the number of subscribers to their networks.

One of the possible directions for expanding the circle of cellular users is penetration into the corporate communications market, namely, the construction of virtual dedicated networks within the general GSM network.

Such technology, in particular, is offered by Siemens, which actively cooperates with the Mobile TeleSystems company”.

Virtual network technology allows implementing closed corporate communication networks designed for a single group of subscribers who mainly interact only with each other, although they can contact subscribers of the general network if necessary.

Dedicated networks will have their own tariffs, access priorities, and the ability to use short numbers will be implemented, which will increase the efficiency of communication.

The introduction of this service in the MTS OJSC network can be expected during this year.

It is no secret that for many heads of security services, whose employees use cellular radiotelephones, the problem is the large number of personal conversations that are not related to the performance of official duties, for which, nevertheless, one has to pay. Therefore, an attractive factor in using virtual network technology for the management of security services is the ability to eliminate non-official conversations of their employees by programming radiotelephones only for communication between subscribers of their network.

Invasion of the professional radio communications market

However, virtual networks are only the first stage of the expansion of cellular systems into the corporate and professional radio communications market. They do not allow solving the main task for professional systems – organizing group radio communications.

Therefore, with the development of cellular networks, technologies adapted to the tasks of professional mobile radio communications could not help but appear, which make communication in a group possible.

One such technology was proposed by Ericsson, which recently presented its new development, called GSM Pro. It allows GSM network operators to provide group radio communication services.

GSM Pro technology involves the use of standard GSM network equipment (switches, base stations, base station controllers), supplemented by three main tools: a special GSM Pro server, a control panel, and special radio terminals that allow you to use all the advantages of GSM Pro technology. The structure of the GSM Pro network is shown in Fig. 2.

BTS – Base Transceiver Station (base transceiver station)
BSC – Base Station Controller (base station controller)
MSC– Mobile Switching Centre (mobile service switching centre)

 

Fig. 2. GSM Pro network structure

As can be seen from the figure, the main addition to the network infrastructure is the GSM Pro server, which is connected to the GSM switch via the E1 interface. The exchange of signaling information between the MCS switching centre and the GSM Pro server is carried out in accordance with the OKS No. 7 protocol.

Dispatch consoles can be connected directly to the server. With the help of such a console, the dispatcher or head of the security service gets the opportunity to promptly manage the actions of their employees performing a task in a large area included in the GSM network communication zone.

The GSM Pro dispatch console is implemented on a standard personal computer, i.e. the dispatch console software can be installed on any PC.

Special radio terminals allow subscribers to work in the mode of a regular telephone, only as professional radio stations with group communication or in a combined mode.

The operating mode is determined by the SIM card used. Ericsson produces special terminals of the R250s Pro brand, equipped with a push-to-talk (PTT) key, a high-power speaker, and also having a durable dust- and moisture-proof case.

GSM Pro technology allows you to group not only GSM network subscribers, but also any other networks, in particular, subscribers of the public switched telephone network (PSTN).

The number of group members cannot exceed 16 subscribers, and the number of groups to which a subscriber has access rights is no more than 25.

Groups in the GSM network are identified using telephone numbers. Information about groups is recorded in the SIM cards of radio terminals and is also stored on the GSM Pro server.

Group radio communication in GSM Pro networks is less efficient than conventional and trunking systems. The time it takes to establish a group connection in GSM Pro is between 2 and 5 seconds. However, this only applies to the initial moment of establishing a connection, i.e. to the initialization of a call.

After establishing a group connection, the GSM Pro server maintains active connections of all subscribers in the group, so any member of the group can transmit information immediately without a pause after pressing the PTT key.

GSM Pro network subscribers can use basic group radio services, which include group, broadcast and emergency calls, as well as additional services, including automatic connection of “late subscribers”, reconnection to a call, dynamic regrouping, call duration limitation and other functions.

In addition, GSM Pro subscribers retain the ability to use a full range of standard GSM network services.

Thus, using GSM Pro networks, security service employees can receive the group radio communication they are accustomed to (though somewhat less efficient) over a very large area in combination with a high level of cellular service.

Not only wider, but also deeper

The expansion of the GSM standard cellular system's communication zone has now also affected underground subway vestibules.

In Moscow, a trial communications subnet is already operating at the stations of the Tagansky transfer hub. By the end of the year, Mobile TeleSystems plans to equip most metro stations inside the ring line with communications.

OJSC MTS also plans to solve the problem of providing communications during train travel inside tunnels by using distributed radiating cables, but this is a more distant prospect.

To ensure communication in the metro, dedicated base stations are used, connected to a network of antennas located in such a way that at any point in the underground vestibule, passage, or escalator, a sufficient level of signal reception from the base station is ensured.

The emergence of communication with subscribers at metro stations, where until now there were no methods of transmitting messages using radio equipment, can expand the operational capabilities of security service employees.

For example, when conducting external surveillance or tracking an object, it becomes possible to transmit information to subscribers located on the surface.

Cost

A sophisticated reader who also uses cellular services may notice that all the described services not only provide new opportunities, but also, to a certain extent, hit the subscribers' pockets.

This is indeed so.

However, each user has the right to make their own economic calculations, allowing them to draw a conclusion about the justification of the necessary costs for using promising GSM cellular communication technologies.

One ​​can only note the general long-term trend of decreasing communication service tariffs. The unprecedented growth in the number of subscribers in 1999 was associated, first of all, with a significant reduction in tariffs by the main cellular operators.

It is clear that this process is not endless, but competition in the cellular communications market is constantly intensifying, and this contributes to lower prices.

In mid-May of this year, the licensing commission of the Ministry of Communications decided to issue another (third) license for the provision of mobile communications services in the GSM 900/1800 standard in Moscow and the region.

Sonic Duo, a joint venture of the Finnish company Sonera Corp and JSC Central Telegraph, intends to invest about $300 million in the development of the network and the organization of the production of radio telephones in Russia and attract up to 160 thousand clients by 2003.

The emergence of a new GSM operator will undoubtedly intensify competition and, in the future, will contribute to lower tariffs.

Let's hope that the promising GSM cellular services will be affordable for most of our readers.

The article was published in 2003 and now it is possible to follow the entire path of GSM technology development 20 years later.