Digital two-way radio technologies such as the Digital Mobile Radio (DMR) standard offer a number of major benefits compared with analogue systems, including improved audio quality, greater functionality, stronger security and better channel efficiency. If you are still using analogue, it is certainly worth considering a switch to digital.
Before we look in more detail at the benefits digital radio provides it is worth noting that DMR is an open standard underpinned by an authoritative suite of specifications developed by the European Telecommunications Standards Institute (ETSI). In addition, the DMR Association has developed and oversees a process for conformance testing of products and for interoperability testing between vendors.
This means end users can confidently purchase DMR products and solutions from Hytera that work with other DMR handsets. The analogue and DMR dual mode function also assists users when migrating, allowing companies to operate mixed fleets of terminals. This provides the freedom to migrate to digital radio at a pace that suits your organisation. But once you’ve moved to digital radio, what advantages do you get?
The first immediate advantage is that you double your channel capacity and therefore the number of users your system can support. This is because DMR operates using two-slot Time Division Multiple Access (TDMA) technology, meaning you get two simultaneous and independent talk paths in the same 12.5 kHz width channel, as opposed to just a single talk path with analogue.
DMR retains the existing 12.5 kHz licensed channel commonly used by land mobile radio around the world, but divides it into two alternating timeslots where each timeslot acts as a separate talk path. Two simultaneous and independent calls can be supported with two radios talking to each other in one slot and another two in the second slot.
The channel maintains the same profile as the old analogue 12.5 kHz signal did, but in effect divides it into the equivalent of two 6.25 kHz wide channels – one for each talk path. This 6.25 kHz bandwidth equivalence therefore makes a much more efficient use of limited spectrum.
Easy migration to digital
DMR was designed to make the transition from analogue to digital easy. If you are an existing 12.5 kHz or 25 kHz analogue license holder, you can simply re-use that for DMR without having to apply for a new licence, as the channel profile remains the same, but as explained you get twice the channels.
This makes migration from analogue to digital a relatively simple process. It should also be noted that DMR can be introduced into existing 12.5 kHz licensed channels without creating any new interference issues.
As mentioned, Hytera hand portables and mobile terminals can operate in analogue, digital and mixed modes. However, users may need to retain existing licenses if they wish to maintain backwards compatibility with legacy analogue radios and systems while transitioning to digital.
Re-use of infrastructure equipment
DMR provides two communications channels with one repeater, one antenna and a duplexer. The existing single channel analogue equipment can be reused for the two-channel equivalent DMR system. No additional repeaters or combiners are needed. Migrating to digital therefore involves minimal investment in new infrastructure equipment.
More power, more battery life
Providing hand portable radios with a longer battery life has always been a challenge. However, the use of two-slot TDMA technology can increase a radio’s battery life by up to 40% compared with analogue terminals. This is because of the power saving way TDMA works.
A single call will only use one of the two available slots, so it only requires half of the radio transmitter’s capacity. The other half, which is not being used for a call remains idle. The transmit time is what really drains the battery, and therefore if one slot is idle, it is not consuming power and that is what helps save the battery life.
Many Hytera DMR products have a sleep mode and also offer other power management solutions, which will help to further conserve battery life. The relatively simple infrastructure required for TDMA solutions when compared with FDMA (Frequency Division Multiple Access) solutions means less energy is used by the overall system, as well as by the radio terminals.
One of the other major benefits of digital radio systems is their ability to support data applications such as text messaging, GPS location features, SCADA and telemetry applications. This ability to support data enhances the value of a digital radio system and provides a greater return on the investment being made.
TDMA two-slot technology is what enables this additional data capability, as one slot can carry voice traffic and the other data traffic at the same time. It is also possible in some higher tier terminals to temporarily combine both slots to either double the data rate to 9.6kbps or to enable full duplex, private calls like a normal telephone call.
The DMR Association has approved a protocol known as AIS or Application Interface Specification, which provides a standardised baseline for a console to interface with a DMR radio system. It makes it much easier and cheaper for third party equipment and applications to interface with DMR.
AIS means DMR end users have more choice and flexibility when it comes to applications. End users can develop solutions specific to their needs without having to develop proprietary interfaces to enable them to work with a DMR radio system.
A simple IP connection can be used to connect a dispatch console. The use of standard IT equipments means the console can be physically separate from the radio system, providing much greater flexibility.
Advanced control features
One other feature the DMR standard enables is the ability to use the second time slot for reverse-channel signalling. This allows information or instructions to be sent to the radio even though the first time slot is being used for a call. Instructions might include priority call control, emergency call pre-emption or to allow the operator of the radio system to take remote control of the terminal.
Better audio quality
A key benefit of DMR digital technology is improved audio quality. Unlike an analogue signal, which diminishes in clarity and usability as it nears the edge of the coverage area, digital signals remain clear to the furthest edges of the radio system’s range.
An analogue user will experience an increasing amount of white noise and more background noise at the coverage edge. DMR digital technology was specifically designed to overcome this, as the DMR Association explains.
“A great deal of effort was put into selecting Forward Error Correction (FEC) and Cyclic Redundancy Check (CRC) coders when developing the standard. With these coders receiving radios detect and automatically correct transmission errors by analysing bits to detect errors.
“The DMR standard specifies over 14 different coders to be used, each matched to different types of traffic. Through the use of coders and other techniques, digital processing is able to screen out noise and re-construct signals from degraded transmissions. Users can hear much more clearly — increasing the effective range of the radio solution and keeping users responsive to changing situations in the field.”
As can be seen, digital radio, and DMR in particular, has many benefits when compared with traditional analogue radio systems. Hytera has a wide portfolio of DMR solutions, radio terminals and accessories that are competitive with analogue products on price and also provide so much more in terms of functionality.
End users also benefit from a fully open standard, offering interoperability and choice to the customer. Hytera fully participates in the DMR Association interoperability testing procedures to enable end users to operate mixed fleets of terminals and infrastructure.
To download our free digital migration whitepaper, please click here.
21 March 2018