Bridging the communication gap

18th March 2015

18 March 2015 - "For DMR systems, an efficient way to bridge the gaps in coverage is site-linking software, which works by allowing multiple independent Tier II DMR repeaters to talk to each other over an IP network..."

Published 18 March 2015

Upgrading your network can feel like a big step and is, naturally, something that you need to research carefully. As part of the DMR team, something that I often get asked is how far away radio users can be from each other and still be able to communicate. Of course, there is no simple answer to this question and radio performance depends on a combination of factors, such as:

  • terrain
  • height of the transmitting and receiving antennas
  • frequency band
  • atmospheric conditions
  • sensitivity of the receiver
  • effective radiated power of the transmitter

Most of these factors are out of our control: you can do little to change your location, for instance, or the topography of the land, but one thing you can control is the technology that you choose.

Users who migrate from analogue to digital radio, for example, often experience a significant improvement in useable range in areas that previously suffered from patchy coverage. This is because analogue signals become distorted as distance from the transmitter increases and signal strength decreases, while digital receivers use error correction to make audio quality more consistent throughout the coverage area. This increases a radio's useable range compared to equivalent analogue devices in the same environment.

However, there will always be circumstances where a little more assistance is needed: coverage might need to extend across multiple sites, and 'black spots' may be experienced on large campuses or even just within large buildings.

The traditional solution to this has been to put in complex distributed antenna systems for conventional radio networks, or extra cells for trunked radio networks like GSM and TETRA. For DMR systems, an efficient way to bridge the gaps in coverage is site-linking software, which works by allowing multiple independent Tier II DMR repeaters to talk to each other over an IP network, such as the internet or a corporate WAN.

When we were developing our own software, Site Link, which launches this month, we listened to feedback from our customers and our partners and tried to address the most common problems they encountered in achieving consistent coverage:

1) We've made it easy to install
Our partners told us they'd had difficulties setting up similar systems in the past, so we've come up with a flexible architecture that makes it easy to deploy new systems or to upgrade existing systems. Site Link uses traditional unicast IP rather than multicast, which can require complex configuration of intermediate routers and relies on the support of the network operator. DHCP and DNS support means that it will work even in an environment where static IP addresses can't be assigned.

2) It's flexible and resilient
We've used a timeslot allocation system, which means that voice transmitted on slot A on one site is not tied to using slot A on subsequent sites, and the fact that the system master is only used for registration, and not for traffic co-ordination, makes the system robust in the face of site failure.

3) It can provide coverage over a large number of sites
Some customers needed systems to support a small number of users located across vast areas. Site Link can support up to 32 linked sites, allowing you to talk effortlessly to colleagues on different frequency bands or at remote locations, country- or even worldwide.

4) It's free!
Site Link is part of our DMR software release R1.1, which also brings several other features, such as Tier II Dynamic which allows you to use the timeslots in your system more efficiently.

Stuart Longley

Stuart Longley
Stuart is a Product Manager, working on the DMR range, and is based in Cambridge, UK. In his spare time, he enjoys exploring the world (countries visited: 32) and is currently attempting to learn Chinese.