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Safety and health in mines research advisory board
Annual review 2006


Mine communications

Enhancing the performance of mine communication and warning systems

Practical work on this RFCS project, RFC-CR-03003 was completed by the end of the year.  It is concerned with achieving improvements in the performance of speech communication systems and auditory alarm and warning systems across a wide range of underground and surface mining applications, together with appraising the application potential for power line communications in mining.  Progress by MRSL during 2006 against the three objectives was:

Improving communication system speech intelligibility.  A review of the feasibility of using Active Noise Control (ANC) systems identified that current potential is limited, but that future application may be possible as technology develops.  Several other techniques for enhancing communication system performance were investigated. These included the concept of “waveshape compression” which permits a significant increase in the audibility of speech in noisy environments. Noise filtering algorithms to filter speech from noise were also appraised, but these offered marginal benefit in the test environment. Several advances on the microphone types employed in underground communications systems were also identified. Each technique was appraised by practical assessment of speech intelligibility in a representative underground gallery environment.

Improving the effectiveness of mine alarms and alerts.  An analytical model and design software were developed to assess the audibility and likely effectiveness of auditory alarms and alerts within a wide range of mining and other industrial environments.  Several psycho-acoustic issues were appraised. These included an investigation of masking phenomena, associated audibility threshold criteria and the sound localisation capabilities of various alarm types. The influence of operating in a reverberant tunnel environment was also assessed. The model was used to evaluate specialised industrial hearing protector designs with increased speech intelligibility over conventional designs.

Power network communication components and their application.  Research results from surface gallery tests showed that the range of currently available high speed (85Mbps theoretical) broadband PLC (Broadband Power Line) technologies is quite limited, and that data throughput falls off rapidly with transmission distance. The decision to install ring fibre optic backbone communication schemes in UK mines is therefore vindicated. The technology was however shown to be useful for short distance applications, such as face machine to gate-end communications. Narrow band power line guided communications using the mine power distribution network to support long distance communications was also shown to be feasible. This could satisfy some low data rate monitoring and control, and emergency applications.

Researching the applications of innovative open wireless technologies

This RFCS Project, CT-2005-00003, has just passed its half way mark.  UK partners are MRSL and RMT. The main target of this research is to innovate mining operations through the widespread introduction of wireless technologies, including smart open wireless sensor networks, wireless digital voice communications and wireless position tracking systems.  MRSL’s work during 2006 has been primarily associated with five topics.

Underground Propagation Studies: Extensive tests were carried out to qualify underground propagation behaviour in underground mines and tunnel environments. The tests were undertaken in different underground environments using classical tunnel attenuation measurements and field mapping techniques, with CW ‘pure’ transmission at 2.3GHz and 5.8GHz.  This work also included assessing field measurements and coverage around representative items of mining equipment and fixed plant. Further tests were carried out at DSKs MÜZ test mine facility using a range of wireless technology equipment, evaluating the overall performance in terms of throughput versus range.

Wireless Technology Options: This research element involved assessment of which types of wireless sensor topology and technology might form the basis of future research and distributed sensor prototype system development. Based on work to date, IEEE 802.15.4/Zigbee technology is still proposed as the development platform for future low data rate sensing, monitoring and control applications. However it is recognised that additional technology types will be needed to address high data bandwidth applications.

Development Platform Selection and Evaluation: Extensive work was carried out on the selection and appraisal of technology platforms suitable for the underground low power wireless sensor network applications identified within this project, e.g. smart sensor networks and active zonal position tracking systems. The characteristics of employing wireless technology for RFID-type navigation and tracking was further considered, examining specific technologies and techniques.  The use of LR-WPAN technology to provide active tracking as an alternative to conventional RFID was investigated. A proposed method of achieving tracking or ‘Zonal Locational Information’ was identified using EmberNet mesh networking LR-WPAN technology, using a beaconing technique.

Robust Antenna Operational Characteristics: Investigations were made regarding the technology options available for compact, microstrip antennas, since any practical application of (embedded) wireless sensing will need to present a small physical envelope, with minimum mechanical vulnerability.

Alternative Power Supplies: A review of alternative power supply technologies was carried out in regard to achieving ‘true’ wireless performance beyond conventional battery supply. The aim of this type of technology is to eliminate the need for external power supply cables and investigate means of power scavenging from other energy sources as a means of either replacing or at least extending battery supplies.

RMT’s work under this Project is to develop, to commercial exploitation, a new version of the m-Comm mines rescue communications system which incorporates a local wireless voice and data link between units worn by the rescue team members and the m‑Comm life line / information transmission system.

RMT’s main finding from initial theoretical studies and laboratory testing was that the system had to have a technology that would overcome multi-path problems, would be low power and operate in the GHz range.  The ideal technology was identified as ultra wide band (UWB) or pulse radio. Unfortunately commercial products based on the UWB technology are not yet readily available. The first fully mass produced single chip UWB will reportedly be marketed in mid-2007.  This will be too late for this project to purchase and integrate into the m-Comm wireless solution. 

The pragmatic solution for m-Comm has been to use a readily available Bluetooth single chip audio configured wireless module.  This wireless technology, based on the CSR range of Bluetooth Class 2 chips and fully FCC, CE and IC compliant, has been found to be remarkably effective in maintaining communications within confined spaces.  The Bluetooth, 1.1 compliant (2.4 GHz), products do require software configuration to fully effect the requirements of the m-Comm link.  Not only must it have a voice link, but it has also to have a data link to forward the press‑to‑talk function to the forward hub within the m-Comm handset.  Most of the software programming of the ‘stack’ or embedded program has been successfully completed.

The interference resistance of the Bluetooth operating system is impressive but not totally fool-proof. It has proved difficult to create blocking interference between two Bluetooth devices but a high powered 2.4GHz device could swamp or overpower the receiver input circuit when placed within less than 10 cm. Encouragingly, the WiFi and Zigbee devices tested for interference with the Bluetooth (Class 2) unit did not cause loss of transmission over a 10m set distance in an open laboratory environment.

The interface specification has been formulated and consideration was given to having a more general interface between the wireless/radio section in order to facilitate upgrades in future and possible incorporation of a future UWB chip.  Circuit designs for; an automatic squelch control modification to both base and handheld units; the wireless interface for the handheld unit; and intrinsic safety considerations have been finalised and critical sections tested.  PCB design work is underway and fully populated units are on schedule for testing in 2007.

There has also been considerable work on choosing the most suitable earpiece and microphone configuration for the system.

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Updated 2009-05-22