The WUCNs promise a wide variety of novel applications for security and monitoring, landscape management, military use, amongst others. One of the main applications of WUCNs is to monitor the underground environment. This includes:

1) Soil conditions such as water and mineral content or the presence of toxic substances
2) Monitoring of above-ground events, such as the presence of people or animals
3) Air ingredient in mine tunnels, such as gas density
4) Water leakage caused by underground river in mine tunnels.

These applications can be described in detail as follows:

• Sports-field turf management - WUSNs can be utilized to monitor turf conditions on golf courses, soccer fields and baseball fields, where the ground surface quality is of critical importance.


 

• Landscape management - Sensors can continually monitor water content near the roots of plants and intelligently activate sprinklers when needed.


 

• Underground infrastructure monitoring - Underground plumbing can be monitored for leaks.


 

• Military applications - Underground pressure sensors deployed just beneath the surface can covertly monitor for unauthorized border crossings. In addition, WUSNs can enable wireless communication in an area with buried landmines.


 

• Security monitoring in mines - Most mine disasters are due to gas explosion. Besides, water leakage (caused by underground rivers) is another threat for mine workers. Sensors can be deployed in mines to monitor the gas density and water leakage to prevent such disasters.


 

• Anti-terrorism in subways and road tunnels - Road and subway tunnels are vulnerable to malicious acts. Surveillance of such tunnels can be carried out by WUCNs.

Figure 1 - Installation of an underground sensor for agriculture using existing wired technology. WUSNs can eliminate surface equipment such as the portion of this sensor which extends above the surface.	Figure 2 - Example of a WUSN in use for monitoring turf conditions at a golf course. Underground sensors do not interfere with play on the surface.

Figure 3 - Mine disasters happen every year all over the world, causing the death of thousands of people. Sensors can be deployed in mines to monitor the gas density and water leakage to prevent gas explosion and mine flood.	Figure 4 - The London subway terroristic explosion exposed that the road tunnels and subways are vulnerable areas to terrorists. WUSNs are needed to surveil the human activity in such tunnels.

Besides monitoring applications, there are more applications for WUCNs in underground mines and road/subway tunnels that are necessitated by human activity in them. Ongoing communication should not be interrupted while a passengers are in the mine or tunnel. Also, there should be a way to transmit messages from within the mine or tunnel effectively for disaster relief.

In this project, we address the key challenges for networking in two classes of underground environments: In soil medium, we focus on the wireless underground sensor networks (WUSNs); while in underground mines and tunnels, we extend our research to more powerful devices and general purpose wireless communication networks.

While existing solutions for underground sensing make use of a wired underground sensor connected to a surface storage device or transceiver, a WUSN device, like a terrestrial wireless sensor network device, incorporates into a single package everything needed for both sensing the environment and processing and transmitting sensor data. WUSN devices are thus different from existing underground sensing devices in that they require no wired link to the surface, utilizing only a buried antenna to transmit their sensor data. WUSNs can therefore provide the following benefits over existing underground sensing solutions:

• Complete concealment - vs. traditional underground sensing methods in which surface equipment is visible.


 

• Increased ease of deployment - wiring between the underground sensor and surface equipment does not need to be deployed.


 

• Real-time monitoring of underground data - many existing solutions utilize surface sensor controllers with no means of communication, simply storing sensor readings in memory until the device is physically retrieved.

Since WUSN devices are completely self-contained within the underground environment, they must be able to communicate through soil and rock using a buried antenna. Unfortunately the underground is a challenging environment for wireless communication. Electromagnetic (EM) waves experience high levels of attenuation due to absorption by soil, rock, and water in the underground. Signal losses are highly dependent on numerous soil properties such as soil makeup (sand, silt, or clay) and density, and can change dramatically with time (e.g. increased soil water content after a rainfall) and space (soil properties change dramatically over short distances). The high rate of EM wave attenuation in the underground means that WUSN devices will need to transmit with higher powers than terrestrial wireless sensor network devices. Besides EM waves, alternative physical layer technologies, such as magnetic induction and seismic waves, may have advantages in soil medium due to their unique characteristics and need to be investigated.

Finding innovative methods of conserving power in a WUSN is of critical importance since devices will likely be difficult to access once they have been deployed underground (making replacement of failed power supplies impractical). Additionally, the unique requirements of underground sensing (e.g. low duty cycle operation) create other interesting challenges for communication protocols in these networks. This project focuses on the design of communication protocols for efficient and reliable communication in WUSNs.

The state-of-the-art in communication and monitoring systems in underground mines and road tunnels is either wire-based or built on the concept of leaky coaxial cable guided systems. However, such systems are expensive to install and maintain. There also exist practical difficulties to set up a wired network within the confines of an existing tunnel. Hence, wireless network using natural wave propagation is a more flexible and efficient solution because it is low-cost, easy to implement and scalable.

There exist some research challenges before such networks can be deployed. EM waves do not propagate well in underground mines and tunnels. Due to the confine of the lossy dielectric ceiling and walls, the propagation characteristics of electromagnetic signals are greatly different from that of terrestrial wireless channels. The channel characteristics may be dependent on:

• Signal frequency

 

• Tunnel shape and size

 

• Position & polarization of transmitter and receiver antenna 

• Tunnel wall makeup (rock, coal, potash, etc) 

• The temperature, humidity and pressure of the air in the tunnel