Mine Mesh Networks Modeling & Simulation

Objective:

To develop network modeling and simulation tools for underground mine mesh networks that can be used to analyze normal as well as post-incident communications between underground miners and the surface.

Overview:

Working with the National Institute for Occupational Safety and Health (NIOSH), NIST is developing simulation tools to evaluate the performance of mesh network communication systems proposed for implementation in underground mines. A mesh network is comprised of interconnected nodes with one or more multihop communication paths between any two nodes in the network. The simulation tools under development will be used to analyze the capabilities of mesh networks under normal as well as post-incident conditions which may arise from an explosion, roof collapse, or other emergency situations.

Mesh Network Technologies:

Mesh network technologies under consideration for implementation in underground mines utilize medium frequency (MF) and ultra high frequency (UHF) propagation between nodes in the network.

• MF mesh networks exploit parasitic coupling of the wireless MF signal to pre-existing metal structures in the mine such as mine rails, leaky feeder cables, and wire-core lifelines enabling one-hop communication distances of up to 3.2 km (2 miles) underground. Propagation along hardened conductors may be robust to emergency situations such as roof collapses. However, bandwidth is limited relative to higher frequency alternatives.
• UHF mesh networks rely on waveguide propagation of the UHF signal along mine entries (tunnels). These networks can support higher bandwidth applications than lower frequency counterparts. No infrastructure is required beyond the powered UHF mesh nodes, however one-hop communication range is typically less than 600 meters (approx. 2,000 ft).
   

Applications of interest for digital mesh networks include multicast voice, text messages, and location tracking information.

Modeling Approach:

A block diagram of the modeling approach is shown below. Using the specifications of the radio under consideration as well as statistics of the noise and interference in a mine, we have developed a physical-layer (PHY) simulation tool in MATLAB with which we generate bit error rate (BER) and packet error rate (PER) tables off-line. Noise models include those for electromagnetic interference for normal operations when mine machinery is on as well as additive white Gaussian noise for post-incident conditions when mine machinery is off.

The BER and PER tables generated off-line by the PHY simulation tool are used by an OPNET-based tool to model link errors. These tables are indexed by the received signal-to-noise ratio, which is computed using the large-scale channel propagation model. The outputs of the OPNET simulation tool are network performance metrics such as end-to-end throughput, delay, and packet loss for a given mesh network configuration and mine map.

Project Progress:

• Observed above-ground demonstration of proposed UHF mesh network (March 2008).
• Observed below-ground demonstration of proposed UHF mesh network at Sentinel Mine, Philippi, WV (April 2008).
• Reviewed detailed documentation of proposed MF mesh network (July 2008).
• Completed physical layer model of proposed MF mesh network (October 2008).
• Developed and demonstrated OPNET model of proposed MF mesh network (July 2009).
• Collected and analyzed underground measurements of MF signal strength in the NIOSH Pittsburgh Research Laboratory Safety Research Coal Mine to refine MF channel propagation model (July 2009).
• Revised MF mesh network OPNET model (October 2009).
• Delivered draft documentation of MF mesh network OPNET model (November 2009).