METIS AEROSPACE utilises well-established and trusted techniques for locating the Signal of Interest (SOI), these being Angle of Arrival (AOA), Time Difference of Arrival (TDOA) and Power on Arrival (POA). Each technique has its advantages and disadvantages, with varying degrees of accuracy for successfully locating different signal types.

Metis Aerospace have developed an integrated solution to maximise the performance of the system by utilising the most applicable algorithm based on the type or modulation of the SOI; the sensor type; and the sensor network deployment, the result of which is displayed clearly and concisely overlaid onto a terrain map, with RF Spectrum activity; geolocation performance info; bearing results to the target; along with other sensor info.  A range of levels of spectrum activity can be recorded and stored for playback, evidence and analysis. The various algorithms are provided as part of the system and can be configured during the installation and commissioning of the system.

This approach maximizes the probability of accurately locating the SOI whatever the signal type or modulation.


An overview of the geolocation techniques utilised as part of the SKYPERION solution are:

Angle of Arrival (AOA)

AOA direction finding, which requires the SKYPERION DF Sensor, provides the operator with a line of bearing to the received Signal Of Interest (SOI) by analysing the signal strengths received between directional antenna elements in the sensor array.  AOA is effective with any RF transmission modulation as it responds directly to received RF power. Advantages include the excellent detection range resulting from directional antenna gain alongside the ability to minimise multipath components to determine improved quality of SOI bearings.

AOA measures signal power so its ability to generate the line of bearing is limited only by the noise floor of the receiver. The SKYPERION utilises circular polarised antennas in its design therefore giving the operator the advantage that it maximises the received signal strength from most transmitting signal polarisations.  This includes all linear polarizations irrespective of orientation, therefore overcoming the polarisation loss against say a horizontally polarised signal suffered by alternative direction finding systems.

Geolocation of the Signal Of Interest is provided by resolving AOA line of bearings from two or more Sensors, combining them at their intersection point to provide geolocation to a single point, in addition to allowing the tracking of the intersection point and therefore the route taken by the Signal Of Interest. When augmented with TDOA geolocation results, AOA provides assured geolocation over the greatest possible range of target signal types.

The line of bearing from any single SKYPERION DF sensor can be utilised to skew the EO/IR camera in the same direction to “stare” along that line of bearing at the target.  In addition, where a geolocation result is found for the Signal Of Interest then all the systems cameras can be automatically or manually skewed round to look at the region where the Signal Of Interest is located.


Time Difference of Arrival (TDOA)

TDOA is a well-proven technique that utilises synchronous time domain captures to determine the relative time of arrival of a Signal Of Interest at different known synchronised receiver locations. The technique is optimal for geolocation over wider areas. Two monitoring receiver points will provide geolocation probability in two dimensions (i.e. approximately along a hyperbolic curve), whereas three or more synchronised monitoring points will allow for  geolocation probability to given confidence level or bounded area. TDOA is more successful for wider modulation bandwidths due to the improved signal correlation properties allowing localisation to a more defined area. An important advantage TDOA offers is that the processing gain of correlation allows successful geolocation of signals which are close to or even below the receiver noise floor. For wide area deployments the timing synchronisation is provided most practically by the Array on-board GPS receiver. Using the DF Sensors, the TDOA geolocation results can be combined with AOA results to provide unrivalled geolocation performance.

Power of Arrival (POA)

POA is a simple geolocation technique that uses synchronous frequency domain captures to determine and compare the instantaneous relative power of a signal at different receiver locations. Given the rapid fall-off in received signal power over distance from a transmitter, the POA technique is optimal for relatively short-range geolocation such as in-building monitoring, where the amplitude comparison yields sufficient differences. POA requires three or more monitoring receiver points to provide geolocation probability to a point. Increasing the density of receiver points significantly improves the quality of the geolocation. POA is effective with any RF transmission type, from unmodulated carrier wave signals to narrow-band or short-burst pulsed transmissions, since the technique relies only on received RF power. POA requires timing synchronization between receivers which can be achieved via a synchronised network locking the nodes together, or by utilising GPS solutions for wider area solution.

Last modified: October 28, 2016

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