There has been a growing need for resilient positioning for numerous
applications of the military and emergency services that routinely
conduct operations that require an uninterrupted positioning service.
However, the level of resilience required for these applications is difficult
to achieve using the popular navigation and positioning systems available
at the time of this writing. Most of these systems are dependent on
existing infrastructure to function or have certain vulnerabilities that can
be too easily exploited by hostile forces. Mobile ad-hoc networks can
bypass some of these prevalent issues making them an auspicious topic for
positioning and navigation research and development. Such networks
consist of portable devices that collaborate to form wireless
communication links with one another and collectively carry out vital
network functions independent of any fixed centralized infrastructure.
The purpose of the research presented in this thesis is to adapt the
protocols of an existing narrowband mobile ad-hoc communications
system provided by Terrafix to enable range measuring for positioning.
This is done by extracting transmission and reception timestamps of
signals exchanged between neighbouring radios in the network with the
highest precision possible. However, many aspects of the radios forming
this network are generally not conducive to precise ranging, so the
ranging protocols implemented need to either maneuver around these
shortcomings or compensate for loss of precision caused. In particular,
the narrow bandwidth of the signals that drastically reduces the
resolution of symbol timing. The objective is to determine what level of
accuracy and precision is possible using this radio network and whether
one can justify investment for further development. Early experiments
have provided a simple ranging demonstration in a benign environment,
using the existing synchronization protocols, by extracting time data.
The experiments have then advanced to the radio’s signal processing to
adjust the synchronization protocols for maximize symbol timing
precision and correct for clock drift.
By implementing innovative synchronization techniques to the radio
network, ranging data collected under benign conditions can exhibit a
standard deviation of less than 3m. The lowest standard deviation
achieved using only the existing methods of synchronization was over two
orders of magnitude greater. All this is achieved in spite of the very
narrow 10−20kHz bandwidth of the radio signals, which makes producing
range estimates with an error less than 10−100m much more challenging
compared to wider bandwidth systems. However, this figure is beholden
to the relative motion of neighbouring radios in the network and how
frequently range estimates need to be made. This thesis demonstrates
how such a precision may be obtained and how this figure is likely to hold
up when applied in conditions that are not ideal
