Wireless underground sensor networks (WUSNs)
are a category of wireless sensor networks (WSNs) with buried
nodes, which communicate wirelessly through soil with sensor
nodes located aboveground. As the communication medium (i.e.,
soil) between traditional over-the-air WSNs and WUSNs differs,
communication characteristics have to be fully characterized
for WUSNs, specifically to enable development of efficient
communication protocols. Characterization of link quality is a
fundamental building block for various communication protocols.
The aim of this paper is to experimentally investigate the
link quality characteristics of the three communication channels
available in WUSNs for underground pipeline monitoring
to gain further insight into protocol development for WUSNs.
To this end, received signal strength (RSS), link quality indicator
(LQI), and packet reception ratio (PRR) are characterized
for the three communication channels in WUSNs. The RSS and
PRR results show that the underground-to-underground channel
is highly symmetric and temporally stable, but its range is severely
limited, and that the aboveground-to-underground/undergroundto-
underground channels are asymmetric and exhibit similar
temporal properties to over-the-air communication channels.
Interestingly, the results show that RSS is a better indicator of
PRR than LQI for all three channels under consideration.