Qualifying Aspects and Advantages of DMR System

12 Sep. 2016   Information

Qualifying Aspects of DMR system
In synthesis DMR digital simulcast system has the following feature:

• Doubling of communications on the same radio channel: maintaining the same ministerial concession for the use of the 12.5 KHz wide radio channel, DMR technology allows to double voice/data traffic. Twice the service with the same cost.
• Total reuse of existing infrastructure: the transition from analogical to digital DMR technology does not require any search for new and additional broadcasting sites to preserve the existing service coverage areas. Radio-electrical efficiency of the two technologies is substantially equivalent; it is indeed possible to improve communications at the field boundaries by equipping the stations with additional receivers to perform diversity reception. Furthermore, to not need new sites means that it is possible to reuse existing power supply systems, the same antennas and the same filters systems as the ones used for analogical stations.
• Dual mode operation: the network is automatically and real time able to discriminate, manage and process both analogical and digital signals on the same radio-mobile channel. Dual mode functionality allows to manage an equipments fleet made of both analogical and digital DMR transceiver and to support advanced services for data transmission, like GPS localization, AVL applications, SMS and files exchange…
• Flexible voice/data management in digital mode: radio resource is optimized because it is shared by voice services and data services; digital voice communications can be performed without any interruption of GPS positioning updating service and with the ability of alarms signalling transit (thanks to the presence of two timeslots).
• Audio band optimization: the full audio bandwidth is available to carry information about the signal to be broadcast on territory.
• Data transmission reliability: the reliability is guaranteed by strength of transmission protocol which provides a set of algorithms and techniques for the maximum guarantee of error free data delivery.
• Upgradability: thanks to advanced and quality modular technology, future introductions of technological innovations will make initial investments safe and will optimize maintenance operations which can be best programmable.
• Insensitivity to components aging: given that DMR base stations are fully digital, every parameter of both transmission and reception is analytically and automatically obtained during self-calibration process of the equipment. This implies a lower maintenance cost because modules do not require regular manual tuning.
• Fleet dynamic management: users can be singularly or by groups addressed.
• Automatic hand-over: mobile units can move inside the operative area preserving communication continuity during the transition between coverage areas of two different repeaters stations and keeping the same radio channel; the call is immediately and contextually delivered to targets, although covered by different repeaters.
• "Direct mode" functionality: for short distance calls, or outside network coverage, terminal equipments (portable and/or vehicular) can communicate with each other on a dedicated channel.
• Configuration flexibility, expandability and extension: complex network configurations can be realized which can fit the orography of the territory through installation of further base stations working on the same radio channel. Furthermore other broadcasting channels can be added to improve the radio traffic management.

DMR radio base station transceivers must comply with ETSI EN300-086 & EN300-113 regulations and with the one about Electromagnetic Compatibility and Safety, and they must have the following characteristics:

• Synchronization: all Radio Base Stations can be fully synchronized by the same network reference.
• Continuous voting: best network signal to be broadcast is performed real time.
• Self adaptive digital equalization: in case of analogical mode, the system can automatically and without any operator implements necessary procedures and techniques, performed by DSP, to equalize the links interconnecting repeaters stations, regardless of the used link type. Adaptive self-equalization can automatically and real-time practically correct any changes in transmission characteristics of carrier in use. In case of digital mode, the system can generate coherent and temporally aligned modulation signals.
• Reconfiguration in case of failure: in case of failure or interruption of connection between radio stations, the station can automatically switch into simple repeater to support local traffic.

Advantages of DMR System
ETSI standard and previous systems compatibility
DMR standard (ETSI TS 102 361 technical specification) is an open standard, defined in ETSI world by a working group made of main PMR equipment producers of the world. DMR standard building followed guide lines of PMR market requirements for digital flexible systems, able to give added value to the present analogical systems, but at the same time to guarantee a gradual migration between the two technologies, making investments and specific operative existing requirements safe.
To this aim HQT DMR repeater DR-9200 is designed with the double standard technology, it is able to work both in analogical and digital way, then supporting both classic PMR terminals and the new DMR ones, with every operating characteristic of each technology (“dual mode”):

• Voice communications with FM analogical modulation and selective calling based on traditional protocols;
• Voice communications and data transmission with 4FSK digital modulation, according to the DMR standard, with 9600 bps gross total speed.

Furthermore the selection of required working mode is fully automatic, this meaning that the repeater is able to autonomously detect if the incoming communication is analogical or digital and can consequently configure itself to work as a PMR or DMR respectively.

Two TDMA timeslots per 12.5 kHz wide channel
DMR digital protocol is based upon two TDMA (Time Division Multiple Access) managed timeslots on the same 12.5 KHz wide radio channel. This means that through the same radio channel broadcast by radio network, two digital communications can be established, and the radio channel capacity is doubled. The use of two timeslots allows also to exchange control signaling while radio communication is in progress, in order to manage, for example, the communication priority or to remote control the terminals functionality .

Greater efficiency of spectrum employment
By implementing two “virtual radio channels” on the same physical radio channel (a couple of frequency), DMR systems increase the efficiency of radio-electrical spectrum employment and they reduce the need for radio frequencies supporting the same traffic amount.

Greater efficiency of battery
Due to the TDMA management of DMR protocol, terminals transceivers consume less power, because their transmission is active for the 50% of time compared to conventional terminals. This happens because the terminal only transmits during one of the two protocol timeslots, while the other timeslot is available for another radio communication or for control signaling transit.

Increased data transmission capacity
Digital modulation requested by DMR standard (4FSK) allows an increased data transmission capacity compared with analogical traditional systems. In fact the system supports data transmission speed up to 9.6 Kb/s over the 12.5 KHz wide radio channel. It is possible then to implement data services with added value between terminals and the operative central, like for example radio traffic management and messages, localization through GPS (Global Positioning System) management, telemetry, with performances greatly better then what analogical systems can offer.

Greater audio quality of communications
Digital modulation employment allows you to get a greater audio quality of digital radio communications in comparison with analogical ones, thanks to the implementation of digital techniques of information coding and error correction. While the audio quality guaranteed by analogical modulation is directly proportional to the received field strength (that is, the weaker the received signal, the poorer the communication audio quality), digital technology allows to obtain the same high audio quality practically all over the coverage area.

Lower costs for licenses and equipments
Digital radio systems based on TDMA (Time-Division Multiple-Access) technology, realize two virtual channels inside the same physical licensed 12.5 KHz wide channel. This means to double traffic capacity, at constant license price, because the physical channel are virtually doubled.

Clearer voice communication over a wider coverage
When signal intensity decreases because of the distance, digital technique of error correction is able to transfer voice and data information without errors or any loss over bigger areas. To increase disturbances immunity and to maximize the coverage area, it is needed however to minimize the “fading” effect due to signal multiple paths, which in digital communication systems is the main cause for rapid degradation of reception quality with decreasing the intensity of received field. To overcome this problem, the space diversity reception technology can be used: the integration of a double coherent receiver, connected to two different antennas immunizes from fading effect because it is statistically not probable to have two contemporary nulls of field on two different antennas, as a consequence of multiple signal paths.

Noise suppression
While signal intensity decreases, analogical signals suffer from distortions producing similar to discharges noise. In contrast, digital receivers simply reject everything can be seen as error and this allows a better listening by users.