DMR Digital Mobile Radio Frequently Asked Questions by TAIT Communications
Does the DMR standard support encryption? The DMR standard is currently being updated to include DES and AES encryption, as well as RC4. This work is carried out by the DMR Association
Q. How does DMR coverage compare with analog?
The coverage of a DMR network is comparable to the coverage of a narrowband analog network. In many instances, the actual coverage of the DMR network is perceived to be better as the voice quality stays the same throughout the whole service area.
Q. Can you combine voice and data on one channel?
DMR supports both voice and data services and on a trunked network, channels can be dynamically allocated to the service that is required. With DMR, priority levels will ensure that traffic with the highest priority will get through.
Q. I have heard DMR suffers from ‘near/far’ issues, multipath and that the maximum coverage is 75km. Is this true?
The maximum coverage of TDMA systems is indeed influenced by ‘near/far’ issues. Almost all DMR vendors, including Tait, provide 0.5ppm frequency accuracy in the terminals so the theoretical limit will then be 150km. There are many other factors that impact on the coverage but the fact is that there are multiple DMR systems deployed with coverage of up to 100km.
Q. Is the DMR standard finalized?
The DMR standard was first released in 2006. It is a live standard and is continuously enhanced to meet new market demands. The standard enhancements are being carried out by the DMR Association and where appropriate are fed back into the formal ETSI standard.
Q. What is the maximum DMR network size?
A Tait DMR network can support a maximum of 20 nodes and a maximum of 2,000 logical channels or 200 sites.
Q. Does the DMR standard support encryption?
The DMR standard is currently being updated to include DES and AES encryption, as well as RC4. This work is carried out by the DMR Association.
Q. Can DMR support GPS/AVL for large fleets?
The DMR standard supports AVL in the form of Short Data Messages (SDM). In a trunked network SDMs are transmitted over the control channel. To increase capacity, multiple control channels can be used or the messages can be transmitted using a traffic channel. This allows the support of a large number of GPS updates.
Q. What is the easiest way to migrate from analog to DMR?
There are various ways of migrating from analog to DMR. One method is deploying multi-mode terminals and changing over site equipment once all terminals on the site can support DMR. Tait terminals support three modes of operation; DMR, MPT and analog FM.?Alternatively, gateways can be deployed between DMR and analog technologies to provide a staged migration. These gateways can be deployed at the node site of the network or at the dispatch end. Various other scenarios are possible and for details please refer to the ‘Upgrading to Trunked DMR‘ white paper.
Q. Is there a certification plan to ensure DMR equipment from different manufacturers will interoperate?
The DMR Association has set up an Interoperability Process (IOP) that will certify terminals of one DMR vendor on networks of another DMR vendor. The IOP process has been well documented in the Association and tests that are carried out are verified by the Technical Working Group of the Association. When all is deemed in order, an IOP certificate is issued. Current valid IOP certificates can be found on the DMR Association website.
Tait DMR has IOP certification with other vendors of DMR Tier 3 equipment.
Q. Does the DMR standard include an interface for dispatchers and applications?
The DMR Association is defining the Application Interface Standard (AIS). This provides the interface for dispatchers, voice recorders and other third party equipment that can be linked to a radio network. It will also provide an interface for IP data applications. A draft of this standard is now available.
Q. When will location services be available?
The Tait DMR Tier 3 solution supports location services using the Short Data Messaging Service on the control channel. This increases the utilization of the control channel while it does not impact on traffic channel availability for voice calls. The interface to the AVL application will be based on the LIP standard, which will eventually be added to the DMR standard. The standard will be documented to allow integration with third-party applications. Clevest location services applications are supported.
Q. Why would an MPT customer upgrade to Trunked DMR?
DMR offers a number of significant advantages over MPT trunked solutions, some are listed below.
• Improved spectral efficiency compared with MPT. 6.25kHz equivalent using DMR.
• Easy upgrade from analogue MPT
• Advanced control features
• Superior audio quality
• More data capabilities - Short data service and Packet data service
• Higher reliability
Q. Why would a customer choose DMR Tier 3 over Tier 2?
• Tier 2 is a conventional offering only
• Trunking offers greater frequency utilisation
• Trunking offers terminal authentication
• Trunking provides talk group options
Source: TAIT Communications
