A lot of financial resources for building of an infrastructure by means of base stations and antenna towers were often required to invest for necessity of radio communication coverage in the case of the classical radio networks by little and major users. Public cellular networks have a certain specifications, which support team works of subscribers, but with certain restrictions. This absence is mostly sensitive in work of some organizations like Police, Customs Service, emergency teams [27], [28].
The solution of these problems lies in private radio trunking networks, which are able to use the same network for several organizations with preserving of secrecy and guarding of data and voice transfer. These networks provide an access to radio channel without great investment because they are able to join one or more systems and to invest to necessary mobile and portable terminals.
Standard for analog private radio networks in Europe represents the group of standards MPT 1317. This group consists of four standards, from which the best known is MPT 1327 one. TETRA (Trans–European Trunked Radio) is the first European opened digital radiotelephony standard defined by ETSI in 1995 [32]. The same way, as public mobile networks were progressively substituted by GSM network in a mobile radiotelephony, digital networks based on new standard will substitute today’s analog terrestrial mobile private networks. TETRA network architecture is in following Figure.
Among basic services of the network belongs the distribution of information for specific group or for each network user (analogy to paging networks). The other services include: e-mails, fax and SMS messages, transfer of data files, and safe access to databases or transport of information from GPS system.
From technological aspect, TETRA consists of two base standards:
TETRA V + D is a radio trunking network standard for voice and data transfer. TETRA PDO is special version of packet transfer in radio channel, permitting of high effective using of limited radio spectrum. TETRA PDO can realize quite high transfer rates (36 kbps), and with superior methods of compression, system can transfer video sequences (for example: police can send signal of video record from the place of accident to police station, where it can be analyzed). System TETRAPOL, like TETRA is a digital private communication network, but it works on different multiple access method (TETRA – FDMA/TDMA, TETRAPOL – FDMA). Standards are not compatible.