What are the digital intercom communication standards? Why use DMR?

By sdga:NiceRF Wireless Technology Co., Ltd

Many users have asked NiceRF Wireless about the technical standards of the digital intercom. This article will explain in detail one by one and tell you why you should adopt DMR. Special reminder: digital radio stations of different standards and different formats may not be compatible even if the equipment adopts the same modulation method. As one of the digital communication standards at home and abroad, DMR has certain advantages, so it is widely used in the fields of digital walkie-talkies and building community security systems.

At present, there are many digital communication standards at home and abroad. The mainstream dedicated digital radio technology standards include DMR, dPMR, P25, TETRA, PDT, etc. Amateur digital radio stations mostly adopt C4FM/CDMA, D-STAR, and other standards.


DMR (Digital Mobile Radio)

Digital Mobile Radio Standard

DMR is an open standard designed and formulated by ETSI to meet the needs of low-end professional and commercial users in European countries for mobile communications. The services supported by DMR include voice services and data services.

The DMR standard divides equipment into Class I, Class II, and Class III. Class I refers to DMR equipment that works in line-of-sight communication mode and is license-free. Class II refers to DMR equipment that works in direct mode or forwarding mode and has a personal license. Class III refers to the use of a central controller for communication control and personal Licensed DMR cluster system equipment. Professional walkie-talkies are used by professional departments for dispatching and commanding. They need to apply for frequency assignment, apply for a radio station license, and pay for frequency occupancy fees. They belong to Class II equipment in the DMR.

DMR channel spacing is 12.5kHz, 4FSK modulation is adopted, the transmission rate is 9.6 kbit/s, multiple access mode is dual time slot TDMA, each time slot is 30 ms, and the speech coding algorithm is not specified.


DPMR(digital Private Mobile Radio)

Digital Private Mobile Radio Standard

DMR is a digital radio standard published by ETSI (European Telecommunications Standards Institute). Solutions that achieve advanced functions through the use of low-cost, low-complexity technologies are suitable for commercial, professional, and public users. The dPMR standard includes two standards, low power, and high power. The low-power standard dPMR446 is a digital public walkie-talkie standard. It only allows handheld devices with a transmission power of no more than 0.5W. It can be used without a license within the specified frequency and has voice and data modes. The dPMR high-power standard is a digital professional walkie-talkie standard, which is suitable for dPMR equipment whose operating frequency is less than 1000MHz and requires a license. There are 3 working modes: Mode 1 is a point-to-point (direct) mode without a base station and other infrastructure support; Mode 2 is a forwarding mode, with one or more base stations used for forwarding or as a system gateway; Mode 3 is a controllable base station Access mode, wide-area multi-point, multi-channel, one or more base station equipment.

DPMR adopts 6.25kHz FDMA technology, 4FSK modulation method, data transmission rate is 4.8kbit/s, speech coding algorithm is not specified, it is recommended to use AMBE++, coding rate 3.6kbit/s.


TETRA (Terrestrial Trunked Radio)

Trunk radio standard on land

TETRA is a European digital communication standard, mainly targeted at government and public security, emergency communications, high-end commercial markets, etc. It adopts 4-slot technology, 25kHz channel spacing, π/4-DQPSK modulation, full-channel data transmission rate 36kbit/s, voice coding 7.2kbit/s, and rich business functions. It has been widely used in the field of government and public security in our country.


PDT (Police Digital Trunking)

Police Digital Trunking Standard

PDT is China's digital trunking communication standard, which is mainly targeted at professional user groups such as public safety, public utilities, industry, and commerce. It adopts TDMA (dual time slot) multiple access modes, 12.5kHz channel spacing, 4FSK modulation mode, and a data transmission rate of 9.6kbit/s. While satisfying basic services, it has added innovative functions such as simulcasting and dynamic frequency resource management, which have been adopted by Chinese public security departments.


Project25 digital intercom system

P25 is the abbreviation of Project25. It is developed and implemented by the American Association of International Public Safety Communications Officials (APCO), National Telecommunications Regulatory Association (NASTD), and Federal Government Users in cooperation with the Telecommunications Industry Association (TIA, a recognized standardization agency). It is mainly used in North America. market.

The evolution of the P25 standard is divided into two stages. The first stage is P25 Phase I, using FDMA technology, C4FM (4FSK) modulation, channel bandwidth 12.5kHz, data transmission rate 9.6kbit/s, digital-analog compatibility; the second stage is P25 Phase Ⅱ, adopts TDMA dual time slot technology, QPSK modulation, equivalent channel bandwidth 6.25 kHz, voice coding adopts IMBE4.4kbit/s, data uplink rate is 9.6kbit/s, and downlink rate is 12kbit/s.

P25 compatibility and portability are good. For example, the P25 digital radio in the first stage is compatible with analog radio. The P25 standard contains requirements for voice and data encryption capabilities. It adopts a large area design, a single station covers a large area, and the number of base stations in the network construction system is small, which is suitable for users with a wide coverage area and complex dispatching functions.

The upgraded version of P25 is P34, which uses OFDM access, QPSK/QAM16/64 modulation, and IMBE voice coding.


Why adopt DMR?

The end-to-end digital nature of DMR means that applications such as SMS, GPS, and telemetry can be easily added to radio equipment and systems.

The DMR standard also supports the dissemination of IP data to enable the development of simple standard applications.

The realization of twice the channel capacity of DMR also adds the key to data applications. Maintaining the existing voice service quality requires the ability to have additional data traffic.

DMR has the following characteristics: efficient use of spectrum resources, large-area networking mode, compatible with the advantages of analog routines. Its business functions are rich, extensible, and backward compatible. The system and terminal costs are lower, the network construction speed is faster, and the overall operation and maintenance costs are lower.

Digital walkie talkie module DMR818

The above are the 5 common digital intercom communication standards and the reasons for the adoption of DMR. The DMR818 digital walkie-talkie module developed by Shenzhen NiceRF Wireless is compatible with the common analog radios on the market, with the function of digital intercoms, and can be used with the same sound The encoder is Motorola compatible, and the details can be found on the official website.

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