The work presented in this thesis has investigated the feasibility, characteristics and potential
applications of low power wireless networking technology, particularly aimed at improving
underground mine safety. Following an initial review, wireless technology was identified as
having many desirable attributes as a modern underground data transmission medium. Wireless
systems are mobile, flexible, and easily scalable. Installation time can be reduced and there is
scope for rapid deployment of wireless sensor networks following an emergency incident such
as a mine explosion or roof rock fall. Low power mesh technology, relating to the Zigbee and
IEEE 802.15.4 LR-WPAN (low-rate wireless personal area network) standards, has been of
particular interest within this research project. The new breed of LR-WPAN technology is
specifically designed for low power, low data rate wireless sensor applications. The mesh
networking characteristics of the technology significantly increase network robustness and
resilience. The self-healing, self-organising, multiple pathway redundancy, and highly scalable
attributes of mesh networks are particularly advantageous for underground, or confined space,
high-integrity safety and emergency applications. The study and potential use of this type of
technology in an underground mine is a novel aspect of this thesis.
The initial feasibility and review examined the current and future trends of modern underground
data transmission systems, with particular focus on mine safety. The findings following the
review determined the ideal requirements of an underground data transmission in terms of
robustness, integrity, interoperability, survivability and flexibility; with wireless mesh
networking meeting many of these requirements.
This research has investigated underground wireless propagation characteristics at UHF and
microwave frequencies in tunnels. This has involved examining electromagnetic (EM)
waveguide theory, in particular the lossy dielectric tunnel waveguide model e.g. (Emslie et al.,
1975 and Delogne, 1982). Extensive tests have been carried out in three different underground
locations (railway tunnel, hard rock mine, coal mine test facility) using continuous wave (CW),
or ‘pure’ transmission at 2.3GHz and 5.8GHz, along with a range of throughput performance
tests using various wireless technologies: IEEE 802.11b, 802.11g, SuperG, SuperG (plus
BeamFlex antennas), 802.11pre-n. 802.11draft-n, and Bluetooth. The results of these practical
tests have been compared with the lossy dielectric tunnel waveguide model showing good
agreement that tunnels will in fact enhance the EM propagation through the waveguide effect.
Building on previous research during the last 30 years into high frequency underground radio
transmission, this work presents a novel investigation into the performance of modern
underground wireless technologies operating in underground mines and tunnels.
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The feasibility and performance of low power wireless mesh networking technology, relating to
Zigbee/IEEE 802.15.4, operating in various underground and confined space environments has
been investigated through a series of practical tests in different locations including: a hard rock
test mine, a coal mine and a fire training centre (confined space built infrastructure). The results
of these tests are presented discussing the significant benefits in employing ‘mesh’ topologies in
mines and tunnels. Following this, key applications were identified for potential development.
Distributed smart sensor network e.g. environmental monitoring, machine diagnostics or remote
telemetry, applications were developed to a proof-of-concept stage. A remote 3D surveying
telemetry application was also developed in conjunction with the ‘RSV’ (remote surveying
vehicle) project at CSM. Vital signs monitoring of personnel has also been examined, with tests
carried out in conjunction with the London Fire Service. ‘Zonal location information’ was
another key application identified using underground mesh wireless networks to provide active
tracking of personnel and vehicles as a lower cost alternative to RFID. Careful consideration has
also been given to potential future work, ranging from ‘mine friendly’ antennas, to a ‘hybrid
Zigbee’, such as, optimised routing algorithms, and improved physical RF performance,
specifically for high-integrity underground safety and emergency applications. Both the tests
carried out and key safety applications investigated have been a novel contribution of this thesis.
In summary, this thesis has contributed to furthering the knowledge within the field of
subsurface electromagnetic wave propagation at UHF and microwave frequencies. Key
characteristics and requirements of an underground critical safety data transmission system have
been identified. Novel aspects of this work involved investigating the application of new
wireless mesh technology for underground environments, and investigating the performance of
modern wireless technologies in tunnels through practical tests and theoretical analysis. Finally,
this thesis has proved that robust and survivable underground data transmission, along with
associated mine safety applications, can feasibly be achieved using the low power wireless mesh
networking technology. Robust underground wireless networking also has potential benefits for
other industrial and public sectors including tunnelling, emergency services and transport
