Magneto-Inductive NEtworked Rescue System (MINERS): Taking sensor networks underground

Wireless underground networks are an emerging technology which have application in a number of scenarios. For example, in a mining disaster, flooding or a collapse can isolate portions of underground tunnels, severing wired communication links and preventing radio communication. In this pa-per, we explore the use of low frequency magnetic fields for communication, and present a new hardware platform that features triaxial transmitter/receiverantenna loops. We point out that the fundamental problem of the magnetic channel is the limited bitrate at long ranges, due to the extreme path loss of 60 dB/decade. To this end, we present two complementary techniques to address this limitation. Firstly, we demonstrate magnetic vector modulation, a technique which modulates the three dimensional orientation of the magnetic vector. This increases the gross bitrate by a factor of over 2.5, without an increase in transmission power or bandwidth. Secondly, we show how in a multi-hop network latencies can be dramatically reduced by receiving multiple parallel streams of frequency multiplexed data in a many-to-one configuration. These techniques are demonstrated on a working hardware platform, which for flexible operation, features a software defined magnetic transceiver. Typical communication range is approximately 30 m through rock.