Think Public Safety

The Power of Power – Maintaining Critical Communications Author: Richard Martin

Created Jun 19 2014, 5:00 AM by Paul Jeffs

A Mission Critical Communications system needs Amps. It seems a very obvious thing to say but without electrical power the base stations supporting systems such as TETRA will not work. Most of these base stations rely on traditional mains power, and there are times when this can fail. Very often this is for a short time, and this can be (and should be) planned for with battery back-up.

But what happens with an extended period of loss of mains power? This happens with surprising regularity and can be triggered by natural events such as storms, ice, or earthquakes. Even more worrying is the threat of cyber terrorism, and this is known to be a major threat to both public safety and industrial organisations. In such situations the need for and load on public safety and utility organisations becomes much greater. With each hour and then day the systems that all of us as citizens rely upon will degrade, our homes will not be heated, the transport system will run out of fuel and our shops will run out of food. Public safety, health services, and utilities must communicate to identify dangerous situations, prioritise their efforts, allocate people, locate and deploy resources.

So how can a mission critical system continue to operate over several days without mains power? There are several solutions, each of which have advantages and drawbacks, and a combination may be the optimum.

Diesel or LPG powered generators. Automatic starting generators have many advantages are relatively low cost. There are practicalities to consider. Fuel levels need to be monitored so that it can be replenished when necessary. In addition fuel is valuable, and becomes even more precious in an extended power outage. The same is true of the generator itself and so security of the site is essential. The generator must be reliable in start-up and so may need to be regularly tested. In very low temperatures the reliability of start-up may become an issue.

One TETRA operator has selected Fuel Cells as the means of providing backup power for protracted mains power loss. The decision was based on several factors. Some of the base stations are deployed on buildings and noise is a factor, Fuel cells run very quietly. Reliable start up in low temperatures is another factor, again fuel cells provide reliable start up. The unit comprises a hydrogen store, fuel cell, and BTS in one secure cabinet. Fuel cells will need to be provided with cylinders of very pure hydrogen, and this and the cost of the fuel cell is a consideration. Nevertheless the deployment has performed well in service for the last 3 years.

Solar power can also be an auxiliary source of power. A solar system could significantly reduce the fuel needed by a generator or fuel cell, but may not be cost effective in all locations and climates.

These solutions can be considered in designing a system for extended power for critical base stations in the TETRA or Critical Communications network. This design will need to take into account many local factors such as climate, base station locations, frequency and length of back-up duration, management and control mechanisms. Motorola has the skills and experience in working with customers to specify, design, install and support such a vital enhancement to the communications system.

Take a look at my recent presentation for Critical Communications Europe to get the full view of ‘Powering TETRA’ including case studies and recommendations.