Sentra DMR Land Mobile Radio System

Digital Mobile Radio (DMR) is an international standard for two-way radios that allows equipment developed by different manufacturers to operate together on the same network.

DMR aims to provide an affordable, low-complexity digital standard to replace analog radio. It was created by the European Telecommunications Standards Institute (ETSI) in 2005 to address primarily commercial market use-cases, whereas Tetra or more expensive P25 LMR solutions are targeted at public safety and other use-cases.

Nybsys offers a full-set of DMR products as part of its DMR portfolio. This includes professional high-end and mid-end portable radios, professional mobile radios and base-station repeaters.

The Nybsys unique offer is an integrated Private LTE and DMR system where DMR radios and regular mobile devices can interoperate on Push-to-Talk (PTT) channels while advanced voice-video communications take place on participating mobile clients. Nybsys Sentra PTT and 4G/5G solutions integrated with DMR offers significant coverage extension and operating cost reduction for a DMR network.

Sentra DMR Mobile & Portable Radios and base-station repeaters

DMR Radio System Overview

The DMR standard was adopted when vendors and users of radio systems recognized that the existing analog trunking standards required updates with modern techniques to provide:
DMR is a complete set of standards which cover voice, data services, and conformance testing. The ETSI DMR Standard defines three different tiers on
DMR equipment works in Direct Mode (unit-to-unit) on public frequencies. Tier 1 DMR devices are best for individuals, recreation, small retail, or other situations that do not require wide area coverage.
This Tier is aimed to be a direct replacement for the analog conventional radio system. These DMR systems operate under individual licenses working in Direct Mode (unit-to-unit) or using a Base Station (BS) for repeating. It has a degree of wide-area coverage and is targeted at users “who need spectral efficiency, advanced voice features and integrated IP data services in licensed bands for high-power communications.”
DMR trunking systems operate under individual licenses with a controller function that automatically regulates the communications. It also supports packet data services in a variety of formats, including support for IPv4 and IPv6. It is ideal for organizations looking to migrate from MPT-1327/EADS/LTR (logic trunked radio) systems or who want the full benefits of managed trunking, voice and data solution.

DMR Benefits

DMR offers several benefits to users, technicians, managers, and the rest of your organization.

Open Standard

DMR is not proprietary to a single manufacturer. This means that competition is possible between manufacturers, not only when a new system is purchased, but over the lifetime of the system. So, if you need to purchase new subscriber units there will always be multiple options and competitive pricing.
DMR interoperability process (IOP) provides for testing of radios to ensure compatibility between manufacturers and offer choices to end users.

Data applications

Not only is DMR capable of transmitting voice, but the end-to-end digital nature of DMR enables data applications such as text messaging, GPS, SCADA, job ticketing and telemetry. As the DMR standard also supports the transmission of IP data over the air, this allows for the easy development of standard applications. In fact, one of the key drivers for users switching to digital is the ability to add business-enhancing data services and applications to radio systems.The radio systems can then be easily integrated into many line-of business applications such as CAD (Computer Aided Dispatch) and work order management.

Advanced control features

The DMR standard allows for the ability to use the second TDMA time slot for reverse-channel signaling. This means instructions in the form of signals can be sent to the radio on the second time slot channel while the first channel is in a call. This capability can be used for priority call control, remote control of the transmitting radio or emergency call pre-emption and gives precise control and flexibility to the operator of a radio system. In addition, DMR offers a higher level of control over the system requisites including called ID, features, priorities, design and operation, allowing custom configuration of the system for a specific environment. FDMA systems cannot deliver similar functionality because they are limited to one path only per spectrum channel.

Better Coverage

DMR offers relatively better coverage, whether across a multisite or single operation. With more range as compared to the analog counterparts, the DMRs are capable of delivering clear communication even in the low signal strength areas.

Superior Audio Performance

DMR technology provides better noise rejection and preserves voice quality over a greater range than analog, especially at the farthest edges of transmission range. An analog signal will gradually weaken and become harder to use as the distance from the site is increased. The user will experience increased amounts of ‘hiss and crackle’ until finally the received audio is completely lost in the noise. A digital signal, however, will remain clear to the edge of coverage. DMR systems use a device called the AMBE+2™ vocoder to convert voice information into digital data. During the digitization process, the background audio noise like sirens, engines, wind etc. typically present in analog systems, is reduced. One of the problems encountered in analogue radios was the relaying of every sound. But, DMRs completely eliminate this problem and deliver crisper & lucid audio with significantly less background noise, distortion or static.

Doubling Of Capacity in Existing Licensed Channels

Using a TDMA access method, DMR enables a single 12.5 kHz channel to support two simultaneous and independent calls, doubling capacity. Because existing licensed channels are used, there is an easier migration from analog to digital.

Longer battery life

One of the biggest challenges with portable devices has always been battery life. Due to greater power efficiency, DMR portables have longer battery life than regular analog portables. With two-slot TDMA, since a call uses only one of the two time slots, it requires only half of the transmitter’s capacity as the transmitter is idle half of the time.

Lighter Devices

Most analog radio devices used to be heavy weight and bulky. But, as the technology is advancing, every discomfort in such conventional devices is being eliminated. DMRs are much lighter in weight and are compact in size. In industries, such as security and hospitality, the discreetness and size of radio hold the utmost significance. Ultra-light and ultra-thin DMRs provide a bigger set of benefits to the user and ensure convenient operation.

DMR Radio System Architecture

DMR Tier II provides wide area coverage with the addition of Repeaters. DMR Direct Mode Operation (DMO) allows radio users within range of each other to communicate directly radio to radio without going through any network. In Tier II, with Repeater-Mode Operation the coverage can be extended.
DMR Radio System Architecture

Repeaters are also needed when signals between radios connecting directly to each other are hampered by obstructions in the line-of-sightbetween them such as trees, buildings, and hills.

A DMR repeater added to the system allows radios to send their communications via a central point which repeats the message to the rest of the system. By installing a repeater high up (often on top of a building) the calls to the repeater are less affected by the obstructions. It also allows radios located far away from the repeater in opposite directions to communicate with each other, effectively increasing the range of the system.

Repeater stations can be connected together by either retransmitting received signals (parroting) or by sending received signals to other repeaters on the system via other methods (internet, unidirectional transmitter, etc). With these methods, the range of the system is only limited by the amount of infrastructure you install.

Diagram: Sentra DMR network architecture

A full DMR network architecture including repeaters is shown below

Use case for integrated DMR-LTE

While DMR systems might effectively support business-critical voice and low-bandwidth data applications, they fail to provide the high-speed data performance necessary to support multimedia applications. The 3GPP 4G Long Term Evolution (LTE) and subsequent 5G standards offer a solution to the need for wide-area broadband networks.

LTE offers real-time access to an array of high-bandwidth applications that simply cannot be supported over narrowband wireless technologies like DMR. These applications include, but are not limited to:

  • High-speed Internet access to network systems and other systems/services available over the public Internet, for things like email and text messaging;

  • VPN access for remotely accessing authorized sites and networks (e.g., the Incident Command System (ICS), and databases/report management systems);

  • Status/information Short Message Service (SMS) and Multimedia Messaging Service (MMS) messaging;
  • IP-based voice communications (including interoperability with legacy and new LMR infrastructure through the use of appropriate gateways) with things like push-to-talk services, biometrics, and telemedicine;

  • Automatic vehicle location;

  • Digital imaging;

  • Streaming video (e.g., remote monitoring, surveillance at an incident, and high-resolution two-way video conferencing); and

  • Full-duplex calling to any telephone device on the Public Switched Telephone Network (PSTN) with functionality comparable to that delivered with today’s cell phones.
Converged devices with P25 LMR, Wifi, LTE, Bluetooth & GPS

By providing access to these types of applications, the LTE overlay further improves communication and collaboration between different public safety agencies and first responders, increasing their response time and efficiency in the field, and improving public safety and security. And, because LTE/5G uses standardized protocols and interfaces, users beyond the range of their home public safety network now have the ability to maintain a connection using a local public safety 700 MHz network or a commercial wireless network.

With Nybsys innovative integration, LTE/5G benefits DMR users two ways: First, DMR radios can continue PTT and other services bridged across vast distances via Nybsys IP-multi-site option. Sentra DMR repeaters communicate with each other over IP to extend the reach.

And second, they can participate in PTT sessions with mobile phone Sentra PTT App users located anywhere. They can choose to use the Sentra PTT App themselves when they are remote. On their mobile phones, other than Sentra PTT, they can take advantage of all of above applications.

DMR with Nybsys Sentra Core for integrated PTT

Nybsys bridges together a DMR network with cellular and wifi networks via LMR and AES Gateways. Nybsys Sentra core-based solution can be used to bridge other types of LMR traffic, such as P25 and Tetra as well, to DMR.

Nybsys LMR gateways can connect P25, DMR, TETRA, VHF/UHF radios to interoperate with neighboring or remote systems. An AES gateway allows Tier III DMR integration. The gateways pave the way to extend DMR coverage and communicate with the Sentra Dispatch and the command infrastructure. This unified communication structure defines a faster and more secure communication method for multiple radio equipment manufacturers without having to buy a single vendor solution.

Diagram: Nybsys Sentra PTT with DMR LMR Interoperability

Integrated DMR Network architecture with Nybsys LTE

For DMR users, Nybsys offers a way to leverage the same functionality that consumer 4G/5G customers enjoy, including greater economies of scale (e.g., a lower cost/bit). A private LTE/5G-based network can be offered in addition to the DMR network to deliver both low-latency PTT and bandwidth-optimized advanced multimedia capabilities.

Nybsys Sentra DMR Product Offerings


Voice Calls

Data Operations

Supplementary service

Device Information:

EP8100 Portable Radio

Portable Radio

EP8000 Portable Radio

Portable Radio

EM8100 Mobile Radio

Mobile Radio

EP5500 Portable Radio

Portable Radio

EP5800 Portable Radio

Portable Radio

EP5000 Portable Radio

Portable Radio

Multi-feature Repeater

Professional High-end DMR System

Professional High-end

Professional Mid-end

Professional Mid-end DMR
Base-station Repeater DMR

Base-station Repeater

Base-station Repeater

Base-station Repeater ER9006

A DMR radio system is a proven technology solution for cost-effective land-mobile-redio communications. NybSys is the only vendor providing a complete communication ecosystem that includes DMR, P25, tactical LTE, PTT App, and a unified web-based Dispatch system. Get in touch with us and get a free demonstration of our solutions.

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