Digital mobile radio - empowering a continent

Emcom Wireless' Business Development Manager, Tony Sipho Sibanda, explains why digital mobile radio (DMR) has become vital in managing the challenges of maintaining a growing network of infrastructure at the continent's utilities.

As many countries in Africa – including South Africa – are facing a growing demand for power and water infrastructure, their utilities are also facing a growing need to better manage and understand their systems.

One of the major challenges in maintaining and managing a utility's infrastructure and resources – especially where electricity is concerned – is the extremely large areas that their communications systems have to cover.

Not only do they need to control their maintenance teams through voice communication, but they also have to be able to control their systems remotely, often via radio.

In the past, this was done via ordinary land mobile radio (LMR) by deploying separate networks for voice and data, and accepting the resulting duplication of infrastructure and operational costs. However, these networks often struggled to deliver the quality of service that is demanded for mission-critical voice and data services, and a system's resources were often locked out by either voice or data from the one service, to the detriment of the other service.

This is unacceptable for real-time mission-critical applications. With the introduction of trunked DMR Tier 3, however, we stand on the verge of revolutionising the way that utilities can manage their manpower while keeping a tight control over their infrastructure networks.

DMR Tier 3

DMR Tier 3 is an all-digital radio protocol that covers the licensed trunked mode of operation. The protocol's strength lies in its ability to deliver crucial voice and coded data signals (SCADA) over the same network at the same time, with each receiving its guaranteed quality of service. This capability allows us to completely rethink the use of wide area professional mobile radio (PMR) voice and data solutions, which deliver combined networks without the limitations of traditional LMR.
The catalyst for this "rethink" is the well-documented channel capacity doubling of DMR's two-slot time division multiple access (TDMA) technology.

TDMA is a channel access method for shared medium networks. It allows several users to share the same frequency channel by dividing the signal into different time slots. The users transmit in rapid succession, one after the other, each using its own time slot. This allows multiple stations to share the same transmission medium (like radio frequency channel) while using only a part of its channel capacity. When combined with the resource-management facilities of trunking, DMR Tier 3 offers a fresh perspective on combined voice and data networking.

It is all about trunking

A "trunked" radio system is a digitally controlled two-way radio system that allows the sharing of a relatively few radio frequency channels among a large group of users by forming "talk groups".
The trunked radio system makes use of the probability that not all the users in an organisation will use the radio at the same time. By assigning a channel to the talk group – and not an individual user – a control channel co-ordinates conversations between users, making effective use of idle time between conversations. This allows many unrelated conversations at the same time, effectively saving time on the specific channel.

The trunking capability of DMR Tier 3 therefore offers call management and network resource optimisation without any human intervention. The centralised configuration of users means operators can manage and monitor the network efficiently, supported by extensive status and capacity reporting.
This, in turn, provides invaluable network visibility, making it simpler to optimise the network by easily adding or moving capacity.

How does this make a difference for network providers and users?

Let's consider a distribution utility's wide area communication challenge – dependable, mission-critical voice and data communications across the entire network. Mobile field workers rely on voice-based, workgroup-centric dispatch services for a safe and efficient work environment under all conditions – from normal day-to-day operations to emergencies.

Over the same coverage area – at the same time – remote devices along distribution lines monitor and control the distribution grid. These devices provide line visibility and management to deliver the required grid reliability metrics. A SCADA control room application polls for, and responds to, remote event notifications from the remote devices. SCADA protocols used by remote devices (such as DNP3 or IEC 60870-5-10x) provide robust communication over narrow band PMR networks.

However, while SCADA messaging is typically only 50-300 bytes in size, message timeouts and latency will generate retries and alarm conditions in 10 seconds, should they be delayed or fail.

This is where trunked DMR's flexible, centrally managed time slot allocation becomes vital. One or more time slots can be permanently allocated to regular, time-critical, SCADA polling activities, with the remaining site resources available on demand for voice and other data traffic.

This effectively means you have two independent network services, deployed over common infrastructure, but realising the benefits of a single vendor, simpler return on interest, and a single network to design, deploy, maintain, harden and secure.

Using a trunked DMR Tier 3 network, an operator has a large variety of options to define the network's operation. This includes:

1. The ability to prioritise network resources for voice or SCADA traffic;
2. Reserving traffic channel resource allocations for voice or SCADA so that dynamic network loading does not impact the quality of service;
3. The linking of logical channels that can deliver higher data rates, especially if the resources are idle;
4. Call pre-emption and queuing based on call priority and network loading; and
5. Efficient support for SCADA signalling via the control channel for sites with low SCADA device counts, while still offering uninterrupted voice call support