DMR (Digital Mobile Radio)
Digital Mobile Radio (DMR) is a digital radio standard harmonized and published in 2005 by ETSI (European Telecommunications Standards Institute) with the task of defining the new generation of equipment intended to be used by PMR (Professional Mobile Radio) users. DMR protocol covers several modes:
– Tier I is intended for direct connection of two stations using general authorization (unlicensed spectrum)
– Tier II is intended for direct connection of two stations or for using base stations as repeaters in licensed frequency band
– Tier III is intended for professional use and accesses the central logic system that automatically manages communications, and is realized in the licensed frequency band
Today, commercially, the emphasis is placed on the licensed Tier II and Tier III.
The standard is designed to operate within two channel bands:
1) 12.5 kHz that is today globally used in licensed networks
2) 6.25 kHz that shall have to be used in the future to ensure frequency efficiency.
The primary goal, and the first entry parameter, in creating the DMR standard was to specify a simple digital system at an acceptable price. The second entry parameter was the request for the new standard to be intended for simultaneous transmission of voice and data traffic. This request is realized by converting the audio signal into digital format, compressing it and sending it, specifically marked, into the digital transmission channel, and sending it together with data. DMR as standard provides the possibility of simultaneous voice and data communication, and is completely adjustable to buyers and their needs.
TETRA (Terrestrial Trunked Radio)
TETRA is an open standard issued by ETSI (ETSI Standard EN 300 392). The goal of TETRA standard was to define a number of interfaces to enable different manufacturers to develop infrastructure and terminals that are fully compatible with each other.
The stations can operate in two modes TD (Time Division) and FDD (Frequency Division Duplex).
The TETRA system is built as a professional (trunking) mobile network. The principal advantages of the trunking system are more users per RF channel as compared to the conventional radio channel, realized by automatic and dynamic assigning of a low number of channels to a larger number of users. The key element of the trunking system is the control unit (trunking controller) that assigns resources (channels) of the terminal unit via one or more control channels. Control channels serve for signalization between the control unit and all the terminals in the network. The control channel is always active; even if the network disappears, base stations have the control channel constantly up.