2 research outputs found
A new iterative algorithm for geolocating a known altitude target using TDOA and FDOA measurements in the presence of satellite location uncertainty
AbstractThis paper considers the problem of geolocating a target on the Earth surface whose altitude is known previously using the target signal time difference of arrival (TDOA) and frequency difference of arrival (FDOA) measurements obtained at satellites. The number of satellites available for the geolocation task is more than sufficient and their locations are subject to random errors. This paper derives the constrained Cramér-Rao lower bound (CCRLB) of the target position, and on the basis of the CCRLB analysis, an approximately efficient constrained maximum likelihood estimator (CMLE) for geolocating the target is established. A new iterative algorithm for solving the CMLE is then proposed, where the updated target position estimate is shown to be the globally optimal solution to a generalized trust region sub-problem (GTRS) which can be found via a simple bisection search. First-order mean square error (MSE) analysis is conducted to quantify the performance degradation when the known target altitude is assumed to be precise but indeed has an unknown but deterministic error. Computer simulations are used to compare the performance of the proposed iterative geolocation technique with those of two benchmark algorithms. They verify the approximate efficiency of the proposed algorithm and the validity of the MSE analysis
RF signal sensing and source localisation systems using Software Defined Radios
Radio frequency (RF) source localisation is a critical technology
in numerous location-based military and civilian applications. In
this thesis, the problem of RF source localisation has been
studied from the perspective of the system implementation for
real-world applications. Commercial off-the-shelf Software
Defined Radio (SDR) devices are used to demonstrate the practical
RF source localisation systems. Compared to the conventional
localisation systems, which rely on dedicated hardware, the
SDR-based system is developed using general-purpose hardware and
software-defined components, offering great flexibility and cost
efficiency in system design and implementation.
In this thesis, the theoretical results of source localisation
are evaluated and put into practice. To be specific, the
practical localisation systems using different measurement
techniques, including received-signal-strength-indication (RSSI)
measurements, time-difference-of-arrival (TDOA) measurements and
joint TDOA and frequency-difference-of-arrival (FDOA)
measurements, are demonstrated to localise the stationary RF
signal sources using the SDRs. The RSSI-based localisation system
is demonstrated in small indoor and outdoor areas with a range of
several metres using the SDR-based transceivers. Furthermore,
interests from the defence area motivated us to implement the
time-based localisation systems. The TDOA-based source
localisation system is implemented using multiple spatially
distributed SDRs in a large outdoor area with the sensor-target
range of several kilometres. Moreover, they are implemented in a
fully passive way without prior knowledge of the signal emitter,
so the solutions can be applied in the localisation of
non-cooperative signal sources provided that emitters are
distant. To further reduce the system cost, and more importantly,
to deal with the situation when the deployment of multiple SDRs,
due to geographical restrictions, is not feasible, a joint TDOA
and FDOA-based localisation system is also demonstrated using
only one stationary SDR and one mobile SDR.
To improve the localisation accuracy, the methods that can reduce
measurement error and obtain accurate location estimates are
studied. Firstly, to obtain a better understanding of the
measurement error, the error sources that affect the measurement
accuracy are systematically analysed from three aspects: the
hardware precision, the accuracy of signal processing methods,
and the environmental impact. Furthermore, the approaches to
reduce the measurement error are proposed and verified in the
experiments. Secondly, during the process of the location
estimation, the theoretical results on the pre-existing
localisation algorithms which can achieve a good trade-off
between the accuracy of location estimation and the computational
cost are evaluated, including the weight least-squares
(WLS)-based solution and the Extended Kalman Filter (EKF)-based
solution. In order to use the pre-existing algorithms in the
practical source localisation, the proper adjustments are
implemented.
Overall, the SDR-based platforms are able to achieve low-cost and
universal localisation solutions in the real-world environment.
The RSSI-based localisation system shows tens of centimetres of
accuracy in a range of several metres, which provides a useful
tool for the verification of the range-based localisation
algorithms. The localisation accuracy of the TDOA-based
localisation system and the joint TDOA and FDOA-based
localisation system is several tens of metres in a range of
several kilometres, which offers potential in the low-cost
localisation solutions in the defence area