Setting up a wireless mesh network in a mine

What is a wireless mesh network?

In a wireless mesh network (WMN), radio nodes are arranged in a mesh topology to create a communication network. This structure may also be seen as a type of wireless ad hoc network. In this context, the term "mesh" denotes a dense interconnectivity between devices or nodes. Typically, a WMN is comprised of mesh clients, mesh routers, and gateways: 

• Mesh nodes are essentially Wireless Access Point (WAP) devices equipped with multiple radio systems. These nodes serve dual roles as both mesh routers and endpoints. They are powered by firmware, which facilitates the exchange of data with other nodes within the network.
• Mesh clients refer to a range of wireless devices, including but not limited to laptops, mobile phones, and tablet computers.
• Gateways in these networks function as the connecting points between two distinct networks that operate on different protocols. They play a crucial role in data transfer, managing the flow of data as it either enters or leaves a network.

Node mobility is generally infrequent in such networks. High mobility can lead to increased time spent in updating routes rather than transmitting data. WMNs usually have a more static topology, which allows for efficient route computation and effective data delivery. Consequently, this network type is a low-mobility, centralized version of a wireless ad hoc network. However, relying on static nodes for gateways means it is not entirely a wireless ad hoc network. Such a wireless mesh network may or may not be connected to the Internet.

Mesh clients in these networks are commonly devices like laptops, cell phones, and other wireless devices. Mesh routers handle the task of directing traffic towards and from gateways, which may be connected to the Internet. The collective coverage of these radio nodes, functioning as a unified network, is often termed a mesh cloud. This cloud's accessibility hinges on the collaborative operation of the radio nodes to form a cohesive network. One of the key strengths of a mesh network is its reliability and the redundancy it offers. If a node fails, the remaining nodes continue to maintain communication, either directly or via other nodes. These networks are designed to be self-organizing and self-healing. Furthermore, they are compatible with various wireless technologies, including 802.11, 802.15, 802.16, and cellular technologies, and are not limited to a single technology or protocol.

What are the prime applications of wireless mesh networks? 

Mesh networks can incorporate both stationary and mobile devices, offering a wide array of solutions tailored to specific communication needs. These networks are especially useful in challenging environments, such as in tunnels, for battlefield surveillance, in high-speed mobile video applications on public transport, and in establishing self-organizing Internet access for communities. A notable application of wireless mesh networks is in Voice over Internet Protocol (VoIP), as these networks can effectively route local phone calls through the mesh. Mesh networks may involve either fixed or mobile devices. The majority of uses for wireless mesh networks align closely with those in wireless ad hoc networks.

Popular applications include:

1. Military units utilize wireless mesh networking for connecting laptops during field missions.
2. Residential electric smart meters, now in widespread deployment, transmit their readings to each other and eventually to the central office for billing purposes, eliminating the need for manual meter reading and physical cable connections.
3. Connecting IoT devices, such as sensors, security systems, smart appliances and monitoring systems can be done via wireless mesh networks; Home smart devices like Google Wi-Fi, Google Nest Wi-Fi, and Google OnHub support Wi-Fi mesh (Wi-Fi ad hoc) networking. Various manufacturers started producing mesh routers for home use in the mid-2010s.
4. Certain satellite constellations function as mesh networks, with wireless links between neighboring satellites. Calls between satellite phones are routed via the mesh, moving from one satellite to another across the constellation, bypassing earth stations. This reduces signal travel distance, thereby decreasing latency and enabling the constellation to function with fewer earth stations. The Iridium satellite constellation, with 66 active satellites in polar orbit, exemplifies a mesh network that provides global coverage.

Wireless mesh networks versus conventional WiFi networks

Wireless mesh networks, when compared to conventional Wi-Fi routers, bring several key benefits:

• Only a single node in the network needs a direct physical connection to the internet.
• Dynamic configuration for optimized speed is a feature of these networks.
• Increased reliability is inherent in their design, as each node interlinks with multiple others. Thus, if a node fails, its adjacent nodes simply reroute the connection.
• Wireless mesh networks adhere to common Wi-Fi standards, such as 802.11a, b, and g.
• Scalability is a significant advantage, allowing for the straightforward addition of more nodes.
• They efficiently extend home Wi-Fi coverage without sacrificing bandwidth, a notable improvement over Wi-Fi range extenders.

However, wireless mesh networks also present certain disadvantages compared to conventional WiFi networks:

• Networks with limited processing power might experience increased latency, as data often has to traverse multiple nodes.
• Absence of a centralized server can lead to complexities in monitoring, managing, and troubleshooting the network.
• Routing and resource management become more intricate due to the decentralized nature of these networks.
• Setting up the network initially can be challenging, requiring strategic placement of nodes, which might involve trial and error.

Wireless mesh networks in mine operations

As we now understand what a wireless mesh network is, how it operates, and how it can be used, it is interesting to ask how they can perform underground in a myriad of shafts and tunnels under rough and difficult conditions to receive and transmit radio frequency signals. 

One of the main benefits of a wireless mesh network is the lack of fibre. In mining operations, this is a valid argument: The length of underground shafts and tunnels can reach several hundreds of kilometres in big mines and laying cables means investment and maintenance. A wireless mesh network enables communication over VoIP protocol: voice and data. As voice is of big value for immediate and hands-free communication between individuals, teams and the control room, data enables even more possibilities. Sensors in the shafts and tunnels can connect to the wireless mesh network and transmit data from gas detectors and dust meters, but can also be used for transmitting machine data. 

Another application of wireless mesh networks may be the real-time tracking of personnel and assets. Tracking is possible when WiFi nodes can triangulate the position of tags attached to a person or asset. Three nodes are necessary for a precise location. 

Maybe the biggest benefit is the scalability in the form of an ad-hoc mesh network. Re-opening, inspecting or creating shafts can be hazardous and is rarely covered with a communication channel. Adding new wireless WiFi nodes to enhance the mesh network is relatively fast and cheap. 

What to think about when using a wireless mesh network in a mine

Reliable communication and accurate tracking are vital to underground safety. Most Western countries mandated systems to be implemented in order to safeguard these crucial aspects of mining operations. The 2006 MINER Act is one of many examples. The same laws require dedicated communication channels with emergency institutions like the fire brigade, police and others. As these channels use a different communication technology (e.g. GSMR), they can't be provided by a WiFi-based wireless mesh network. 

Furthermore, wireless mesh network nodes need a power source to work. If they are supplied with battery power, they need to be charged occasionally on the spot or exchanged. If a node goes down because of lack of power, it may affect the entire mesh network as backup nodes may not be available in the range: Signals from other areas are blocked by the surrounding rock, and doubling nodes doubles the costs - investments and maintenance. The only reliable source of power is a power supply system with built-in UPS. Of course, this increases the infrastructure costs again but secures the availability of the network. 

Using power cables also limits the application of ad-hoc wireless mesh networks. For a limited battery lifetime, such ad-hoc networks make sense, but for permanent operations, it means constantly changing the batteries. 

Triangulation may work perfectly in a bigger room with three nodes, but in a narrow, long shaft, it is a try-and-error process to figure out the proper position of the nodes for the best signals. As with all triangulation technologies, it is mandatory to define and mark the exact position of the node to create a positioning frame. Otherwise, pin-pointing a position is not possible. Therefore, triangulation in ad-hoc mesh networks is not feasible without transmitting the exact position of the new ad-hoc node. This takes time and skills. 

Takeaway

In the context of mining operations, wireless mesh networks, initially developed for military use, offer exciting possibilities due to their dynamic node-to-node communication. These networks, consisting of mesh nodes, clients, and gateways, ensure continuity in communication, even when individual nodes fail. They are particularly suitable for challenging environments, providing robust VoIP communication and facilitating real-time data transmission from various sensors. Additionally, these networks support efficient asset and personnel tracking through triangulation.

However, implementing these networks in mines comes with challenges. Compliance with safety regulations, ensuring a stable power supply for nodes, and the complexities of node placement and triangulation in varying mine layouts are critical considerations. Despite these challenges, the scalability, flexibility, and reliability of wireless mesh networks make them a valuable tool for enhancing operational efficiency in mining settings. In many cases, zone-based monitoring solutions are more reliable, less complex and economically more reasonable alternatives when it comes to underground mine safety (read more about miner tracking). 

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