Wireless communication networks are essential for surface mining, whether it is for open pit or in situ. The need for a trusted and secured wireless connection is critical for efficient and cost effective operations. Providing an ubiquitous wireless umbrella for surface mining is complex since the mine topography and morphology is ever changing due to the movement of large equipment and vehicles, changing terrain as the mine grows, signal blockage and multipath reflections, and a myriad of other factors that combine to make for a harsh and dynamic landscape for RF coverage.
Modern technology and superior design can alleviate these issues and make the job easier. The best practice approach is to treat the mine site with a “distributed antenna system” or DAS. A DAS system is a collection of antenna systems operating in harmony with coordination of signals and traffic within the mine’s geographic footprint. These seemingly disparate last mile hotspots are linked with a middle mile backhaul technology, typically also wireless or optical fibre. A centralized controller administrates each node so it can supervise the transmit power levels, the coverage patterns, as well as coordinate the traffic flows via the best available node. The hotspots use electricity to operate, preferably from an AC power source or from some energy harvesting solution like wind or solar generation, or a genset, supported by an uninterruptible power supply (UPS).
In the Figure 1, we see four discrete wireless antennas within the coverage area. These patterns overlap in order to provide 100% coverage of the area. The range or distance for each coverage pattern is nearly 600 feet / 185 metres. Range varies due to the nap-of-the-earth topography and the blockage from the morphology. Topography is the mapping of the surface of the earth, whereas morphology is the study of everything on the surface of the earth. Both are considered only within the space of the mine site when we model the signal coverage. Topography features includes holes, hills, valleys, cliffs, berms, water, roads, rocks and boulders, cut lines, tailing piles, and other surface features. Morphology includes man-made items applied to the mine site surface, such as various pieces of mining equipment like articulated dump trucks, rigid haul trucks, excavators, large shovels, loaders, graders, dozers, conveyors; power lines and poles, buildings, head-frames, hoist rooms, trailers, etc.
Figure 2 is an example of an open pit mine. With special modelling tools that layer the terrain surface underneath the Google Maps image, we can predict coverage and optimize base station positions before installing anything. In this way, we can determine the ideal placement and the number of base stations to blanket the terrain with a comprehensive coverage pattern.
The open pit mine shown in Figure 3 is the same pit as in Figure 2, but with a predictive model of the coverage based upon signal strength. This image above is an actual coverage map of an open pit mine with a Wi-Fi umbrella. With just five base stations, 100% of this huge pit is properly covered and can accommodate communications to all of the devices, equipment, and workers.
When using multiple towers in a concentrated area, interference can and will occur. With conventional Wi-Fi not making use of DAS, we can model the interference (in red) and as seen in Figure 4. However, if intelligent DAS is applied, then base station coordination is possible supported with adaptive transmit power levels, varying modulation / forward error correction, and beamforming of the antenna patterns. With all of these features used, the interference can be mitigated and no longer be a factor in the design.
The DAS network needs to manage all of these issues under coordinated computer control. The coverage patterns from each antenna site overlap to the adjacent patterns in order to provide adequate coverage and to compensate for obstructions and reflections. Therefore, the DAS network needs to be aware of the location of the nodes too in order to adjust the RF signal levels to ensure reliability and availability.
Surface mine engineers use maps for planning, design, and engineering. They are typically updated annually. These same map data sets used to plot the mine surface for Figure 5 can be used as data layers in the coverage propagation modelling tools to plan the signal coverage for the DAS network.
Once we have the terrain data for the mine pit, we can lay the predictive coverage onto this 3D model and manipulate it through 360° for validation that the coverage is comprehensive and complete. In Figure 6, the predicted coverage for this article was texture map rendered and applied to a 3D model of the mine site from Google Earth to demonstrate what is possible. As you can see from the two small grey patches within the mine, these are holes in the current version of the coverage. They can be accepted or the base station positions moved to fill in these coverage holes.
As the mining equipment moves about the site, connectivity needs to be maintained so data traffic vital to the mine operations can flow as necessary. Data traffic can include telemetry from the vehicle for machine health, which includes tire pressures, transmission status, engine status, and command, and control for semi-autonomous or fully autonomous mining including: speed, direction, RPM, location, load weight, alarms, etc. All of this data traffic must arrive to the control site and the operator in a timely manner to permit proper control and precision adjustment of the equipment. Machine health parameters help operators to get ahead of costly breakdowns and to plan preventive maintenance of the equipment.
None of this is possible without trusted, secure, reliable and available wireless coverage as seen in Caterpillar Command for Dozer Control Console shown in Figure 7.
Figure 7 – Caterpillar Autonomous Mining Command Console
What are the core design issues of any DAS network solution? They include:
- Antennas and base stations
- Modulation and Forward Error Correction
- Data Rates
- Backhaul networks
- Interference and coverage challenges
- Signal enhancement features (MIMO)
- Ruggedized equipment
- Traffic – volume and types
- Node types
- Mine site size, shape, and growth
- Concentration of work within the mine site
- Marshalling of equipment for best efficiency
- Back office systems and tools
- Linkage to third party service providers
Wi-Fi is fast becoming the most popular DAS technology. It is ubiquitous and there are so many devices available today to connect to Wi-Fi that it is the most cost effective means to cover the modern mine site as seen in Figure 8.
Figure 8 – Komatsu
Wi-Fi is a trusted and mature standard, but at the same time it is still evolving as a standard and we eagerly expect many new developments to become available, so it is only getting better. Most are familiar with the IEEE 802.11a/b/g/n standards that are found in most offices, homes, coffee shops, and just about everywhere that people gather. However, newer standards from the IEEE 801.11 family are emerging that will greatly enhance this technology. A few of the emerging examples include:
- 802.11ac – far more data rates up to 433.3 Mbps per stream
- 802.11ad – used in the ultra high spectrum in the 60 GHz band to provide stunning 7 Gbps capabilities, but likely for shorter distances compared to the lower 2.4 GHz and 5.0 GHz standards
- 802.11af – for use at lower frequencies below 1 GHz for far greater coverage ranges within the TV white space (the gaps between over-the-air TV channels)
- 802.11ah – for use in the sub 1 GHz bands, specifically the ISM band at 902 to 928 MHz in North America resulting in better range and coverage compared to the traditional 2.4 GHz or 5.0 GHz bands
Figure 9 – MDPI.com
The backhaul networks can make use of commercial WiMAX based star network base stations or lower cost optical fibre, including the newer PON (passive optical networks). Due to the size of a surface mine, both single mode and multimode optical solutions can also work well. Wireless mesh relays as seen in Figure 9 are also an option.
These new DAS networks are being designed for unified communications so many applications from both IT and OT are found on them. Therefore, classic baseband networking issues like QoS, VLANs, IP addressing schema, network and application segmentation, guest networks, employee and contractor networks, VPNs, IDS, IPS, firewalls, and more will all be a part of the design. Voice over IP and video surveillance are challenging traffic types to manage over any network, so understanding the ballistics of these applications is critical to the DAS design.
It is now possible to plan, design, engineer, and implement a strong wireless network using DAS. Surface mine operators can now provide uniform coverage at every corner of the mine site. Coverage nulls from past conventional wireless implementations can be eliminated and interference issues can be mitigated. These DAS networks can be robust, secure, and available to the levels that operators demand. New capabilities all aimed at reducing the cost per ton are now possible as a result of these DAS systems. This infrastructure can greatly enhance performance and drive profits. Intelligent or smart DAS networks are now a reality.
About the Author
Michael Martin has more than 35 years of experience in broadband networks, optical fibre, wireless and digital communications technologies. He is a Senior Executive Consultant with IBM Canada’s GTS Network Services Group. Over the past 11 years with IBM, he has served in the GBS Global Center of Competency for Energy and Utilities and the GTS Global Center of Excellence for Energy and Utilities. He was previously a founding partner and President of MICAN Communications and before that was President of Comlink Systems Limited and Ensat Broadcast Services, Inc., both divisions of Cygnal Technologies Corporation (CYN:TSX). He holds three Masters level degrees, in business (MBA), communication (MA), and education (MEd). As well, he has diplomas and certifications in business, computer programming, internetworking, project management, media, photography, and communication technology.