We now live in a digitised world, whatever we do or wherever we go, we expect to be constantly connected via the internet for instant communication, high bandwidth communication systems are accessed through Wi-Fi or our country LTE providers. But what we take for granted above ground is not always available for workers in mines and tunnels underground.

So What About Mines & Tunnels?

In a modern underground operation, whether this is an operational mine, or a tunnel construction project, there is an every increasing drive towards increased productivity, and more importantly zero harm for personnel working underground. A modern high bandwidth communication system, if planned and deployed correctly, is a very useful platform for helping with productivity and workers safety – providing service such as VoIP, personnel and asset location tracking, telemetry information from mobile plant, gas detection monitoring, pump monitoring and control.

Many mining and tunnelling projects are starting to take advantage of high bandwidth systems, with Wi-Fi systems being installed underground, sometimes alongside existing leaky feeder infrastructure.

Wi-Fi Propagation Underground

Over the previous three months, our engineers at MTI Tech Ltd have been testing Wi-Fi underground, to understand the effect on the underground environment on the propagation of the RF signals. With the very kind help of industry associates, we have been fortunate to test at four underground sites in the UK.

Each test site was very different, the caverns and tunnels ranged from 2m up to 5m, and the minerals/materials that the tunnels were constructed of a range of different materials, some man-made and some natural.

Mining Communication Products

Mining Antennas

During the testing, MTI Tech used Poynting antenna products – the uni-directional HELI-21 underground antenna, and the bi-directional HELI-22 antenna.  The antennas used were specially chosen as these antennas were designed specially for mining and tunnelling projects, and are of circular polarisation. These antennas are best suited to mining and other types of harsh RF environments. In some cases where conventional antennas are used, the RF propagation is quite limited and diminishes rapidly down the tunnel.

Mining Wireless Access Points (AP)

We tested on both 2.4GHz and 5GHz using the MTI Wireless Switch and the Rajant ES1 Wireless Mesh Node.  The main difference between the two products is that the Rajant device is a mesh network, this product does not require a fibre connection at every node.

Mining Radios

To check the voice coverage underground, we were kindly loaned some radios from Icom UK, along with the relevant controller. The Icom IP radio handsets were of lower RF power than the Wireless AP’s, so this was taken into account when calculating the RF budgets and distances between each AP.

Wi-Fi Test Results

The test results obtained during the extensive were very encouraging. With the larger caverns and a good line of sight, a distance of approximately 600m from each wireless AP was achieved, in affect this would mean potential spacing of each AP at around 1Km. RSSI levels of -62dBm were achieved at 400m away from each AP and -68Bm at approx. 590m distance.

Not surprising, where no line of sight was available, the distances achieved was much reduced.

Within the underground environment, where the tunnel was relatively smooth, but we did not have line of sight, we did achieve some good distances – in excess of 300m from the AP’s. The tunnel seemed to act as a waveguide for the RF signal.

For further information please contact MTI Tech Ltd.