While advancements in communication technologies now provides underground mine operators with more options for increased coverage and improved connectivity, there are several common challenges that need to be taken into consideration when designing a communications system.
In underground mining operations, communication systems play a crucial role for personnel safety and maximising productivity. Safety-critical and operational related systems rely on the communication system for:
- Voice communication(analogue/digital)
- Data communication
- Personnel and Asset tracking system
- Environmental monitoring system
- Autonomous machinery
- Remote Telemetry
- IoT (Internet of Things)
By its very nature, the different applications require various level of bandwidth, latency and reliability.
Due to the unique environment of underground mines, there are several common challenges that need to be taken into consideration when designing a communications system including:
- Long distance ramp/decline, shaft or tunnel where reflection/refraction cause loss in signal strength;
- Poor line of sight – nature of declines;
- High temperature, humidity, dust, and gas concentration;
- Noise, vibration, explosion in confined space which degrades the electromagnetic signal quality;
- Wireless RF coverage modelling/prediction;
- Equipment compliance with the appropriate protection level to work under the mine’s specific
hazardous area rating;
- Underground power supply constraints; and
- Dynamically changing environment as the underground mine expands.
2. Wireless Technologies for Underground Mines
The major wireless communication technologies fit for use in underground mining can be broadly classified into two categories:
i. Through the Earth (TTE)
ii. Through the Air (TTA)
i. Through the Earth (TTE)
The TTE technique utilises a transmitting loop antenna on the surface of the mine and transmits on ultra-low frequency (ULF) signals (300-3000Hz). It supports tracking capabilities and is not vulnerable to fires or explosions in the underground mine. TTE is widely used and effective for personal tracking device (PED) system for emergency messaging and alert. The PED system is receiving only which is one-way communication. On the downside, the applications of TTE are limited as the data rate is extremely low due to operating on the ULF.
ii. Through the Air (TTA)
TTA uses radio frequency channels for communication between multiple nodes requiring no physical connections. TTA is also being harnessed to support new and emerging mining operation applications which rely on wireless communications systems. While an effective option, RF signal propagation, attenuation and reflection/refraction can be highly influenced by the underground environment.
This paper will explore a range of solutions over TTA for underground mining including:
- WiFi Mesh
In addition, there are different type of antennae that can be deployed to improve the coverage within an underground situation. These include:
- Bi-Directional Amplifier
- Leaky Feeder Antennae
- Distributed Antenna System
- Directional Antennae
Two-way-radio systems are widely used in underground mines for voice communications. All analogue and digitally modulated two-way radios, including handheld, vehicle mounted or base station transceivers, must operate in the licensed Australian land mobile VHF and/or UHF frequency bands. While two-way radio is a highly effective solution for voice, increasing data communication requirements mean that VHF/UHF is less suitable for data transmission due to limited data transfer rates.
LTE (4G) cellular networks can provide high bandwidth data and voice mobility services over low frequency bands that allows a better propagation in the underground mining environment, delivering faster, more advanced wireless technology application. Because an LTE network provides a high capacity, QoS enabled and highly available network, it opens a suite of new capabilities and possibilities to cost effectively enable automation and remote operation technologies for underground mine operations.
Advantages of enterprise LTE:
- Low latency to support critical system, voice, video and autonomy
- Licensed frequencies used (even underground), effectively eliminating the risk of network interference and intrusion.
- Designed for seamless mobility.
- High reliability and availability to support critical systems.
- The ability to converge voice and data communications while maintaining traffic separation and QoS
While there are several advantages to an LTE network, it is a more complex system to design and deploy in contrast to WiFi solutions.
A wireless Mesh Network (WMN) is created through the interconnection of wireless access points which are installed in fixed locations or on mobile vehicles. Each network user (AP) is also a provider, forwarding data to the next node. The networking infrastructure is decentralised and simplified because each node need only transmit as far as the next node.
The key benefits associated with a WiFi Mesh Network include:
- Instant, automatic formation of wireless networks;
- Self-forming, self-healing, and self-balancing;
- Lower infrastructure and operational costs;
- Compared to LTE, WiFi Mesh AP provides smaller coverage area and lacks over the air QoS;
- While the size of the mesh network expands, it divides the bandwidth; and
- Unlicensed frequencies mean susceptibility to interference
The drawback of WiFi Mesh is it has no capacity for critical voice communications, and the technology is not designed for seamless mobility.
LTE and WiFi are standards based on wireless technologies that, in theory, allow a combination of vendor equipment. However, there are also proprietary wireless technologies that may provide some advantages.
For example, the use of MPLS technology and seamless mobility (with make before break handover) may deliver performance superior to WiFi – but not that of a LTE network – and be delivered at a WiFi price point. While there would be no requirement for licenses or a distributed control plane, vendor-lock is one disadvantage of this approach.
3. Riding the New Wave: Antenna Options
Several antenna options are available with some having significantly evolved over the last two decades and are proving to be better solutions for transmission and coverage in an underground setting.
A leaky feeder system works by utilising a purposemade coaxial cable, also known as a radiating cable, as the antenna. The coaxial cable is constructed with a slot cut into the outer shielding to transmit and receive radio waves.
Effectively, this turns the entire cable into one long antenna emitting and receiving along the full length. The leaky feeder system is normally installed with a splitter and terminator at the end of the cable, along with amplifiers to extend the coverage range.
The conventional leaky feeder system streams VHF/ UHF two-way radio to serve the voice communications or low-bandwidth data transfer. While in a modern communications system, a leaky feeder set-up can also be used as the antenna for an LTE deployment.
Distributed Antenna System and Bi-Directional Amplifier
Distributed Antenna Systems (DAS) are comprised of a series of radio heads strategically positioned around a targeted location where there is a need for increased coverage. Each of the radio heads within the DAS are then routed to radio base station(s). There are a number of advantages of using DAS in underground setting including:
- Better defined coverage;
- Fewer coverage holes;
- Same coverage using a lower RF power;
- Individual antennae do not need to be as high as a single antenna for the equivalent coverage; and
- Directional antennae (Panel or Yagi) can be used.
Bi-Directional Amplifiers (BDAs) are signal boosters that support two-way radio communications in confined settings such as underground mines, tunnels, stairwells and multi-level car parking.
When used in tandem with a DAS system, BDAs act as amplifiers, or repeaters, that boost and distribute a signal over a range of radio frequencies, effectively creating a network of separate antenna nodes to extend coverage.
While advancements in communication technologies now provides underground mine operators with more options for increased coverage and improved connectivity, there is no one size fits all model.
Not withstanding that LTE enables future-proofing, other cost-effective technologies can provide viable solutions depending on the mine’s production, lifecycle and other drivers.
An upgrade to a mine’s communications system should be customised for each underground scenario taking into consideration its unique operational needs. A well designed and engineered solution can deliver on the communications needs based on the specific use case of the organisation.
About Titan ICT
Titan ICT is an Australian-owned company specialising in strategic ICT advice, systems integration and technical support services to deliver high quality integrated technology and business solutions. With a proud record of delivery since 2003, we have a national footprint with offices located Perth, Brisbane, Melbourne and Sydney.
From the outset the decision was made to focus purely on ICT disciplines providing trusted advice and engineered solutions that tackle technology transformation and maximise the potential of any project, big or small.
As a result, we are at the forefront of new technologies by constantly turning to innovation and ingenuity for the development of tailored, leading-edge solutions that support the operational and strategic objectives of the companies we work with.
By working with us, you too can enjoy the successthat results from the bringing together of worldclass skills, best in breed products and practical know-how in planning, managing and delivering complex scopes of work.
The author only represents himself as competent professional in the planning, design and implementation of Telecommunications and Information Technology systems, networks and practice. Any statement provided which may be of a legal nature is only offered as an opinion based on the author’s understanding of the law and how it may apply. The author has made every effort to identify all relevant and available source data in the preparation of this document. All surveys, forecasts, projections and recommendations are made in good faith on the basis of information available at the time. The author, its agents, licensee and/or other representatives disclaims any liability for loss of damage caused by errors or omissions, whether such errors or omissions resulted from negligence, accident or other causes. Neither the author, its agents, licensee nor representatives will be liable for any loss or other consequences (whether or not due to the negligence of the author or their agents) arising out of the use of information in this report. No responsibility is taken for the accuracy of this information in relation to pricing or functionality of products and services described in this report. Readers should confirm with the appropriate service provider as to the validity of the information and any variations which may have taken place since publishing.