Mining Contract: Advanced Software Radio Techniques for Improved Range and Reliability of Digital Through-the-Earth Communication Systems

Contract Status & Impact

This contract is complete. To receive a copy of the final report, send a request to mining@cdc.gov.

The Mine Improvement and New Emergency Response Act (MINER Act) of 2006 calls for mines to have emergency response plans that “provide for post accident communication between underground and surface personnel via a wireless two-way medium.” Mines have installed systems that are significantly better than what was available in 2006; however, they all depend on infrastructure that to some degree includes copper wire or fiber links and a line of sight between that infrastructure and the worker. Unlike traditional communication methods using higher frequency radio systems, through-the earth (TTE) radio systems based on very low frequency (VLF) communication using electromagnetic induction allow underground workers to communicate without having “line of sight” or a physically wired or fiber connection, other than the antenna. The use of frequencies in the 0.3 to 9 kHz range allows TTE radio systems to penetrate strata that would typically block traditional radio signals.

TTE radio systems can support voice, text messaging, and data in either duplex or half-duplex (push-to talk) configurations. The current state of the technology supports voice communication up to a maximum of approximately 1,000 feet and text or data in excess of 1,000 feet. The operational range of TTE radio systems is limited by the external or environmental magnetic noise, which in many instances is man-made, originating from electrical machinery and power lines. This makes it difficult to test the emergency link or use it for operational purposes.

The Office of Mine Safety and Health Research (OMSHR) contracted with Vital Alert Communication, Inc., for the development of an Advanced Software Radio (ASR) prototype system designed to demonstrate improved link performance and range in the presence of electrical noise, compared to the TTE radio systems developed to date. The prototype hardware is based on the Vital Alert Communication C1000-IS and CanaryGo products. The C1000-IS is designed to be intrinsically safe in compliance with the requirements of 30 CFR Part 23 and MSHA ACRI2001. The CanaryGo is used above ground. In this project, the ASR performance was evaluated against the radio used in the standard versions of these products.

In the final phase of this research, the ASR was taken out of the laboratory and tested in two different mines in order to characterize its performance in realistic operating environments. The in-mine tests showed the improvement to be in the 10 to 15 dB range, thus verifying the laboratory tests. Based on the evidence of these results, the Inter-Harmonic Modulation (IHM) technique—a multi-carrier modulation technique created by Vital Alert specifically for TTE communications—has been shown to be capable of providing a significant and demonstrable improvement in the quality and reliability of TTE communications in the presence of Power Line Noise (PLN) in the coal mine environment. Further improvement should be possible, and Vital Alert therefore plans to continue the development of IHM to the point where it can be introduced into commercial products.