Real-time wireless multi-hop protocol in underground voice communication

The underground communication in tunnels and mines is very challenging due to the hostile nature of the environments and to the propagation issues that electromagnetic waves suffer there. Communication is often unidirectional (e.g. in mines) or very costly (e.g. leaky feeder in road tunnels) and hard to install and maintain. This work proposes the use of multi-hop ad-hoc networks to provide multimedia communication between mobile nodes in such a hostile environments, relying on a complete hardware/software, cheap and easy-to-setup platform that can be used both as temporary or fixed infrastructure or as communication backbone in emergency scenarios like mine accidents or a tunnel collapse. The communication is based on the Real-Time Multi-hop Protocol (RT-WMP) and its QoS extension executed over several nodes equipped with specific hardware. This protocol manages delay sensitive messages and the node mobility across the network while the QoS extension is responsible for allowing the end-to-end voice communication. The specific topology and situation have driven to a specialization of RT-WMP to better perform in this type of environments, taking advantage of the a priori (partial) knowledge about the topology. This proposal was tested in a real application in the Somport tunnel, the about 8 km-long railroad linking Canfranc, Spain with Pau, France.