METIS AEROSPACE utilises well-established and trusted techniques for locating the Signal of Interest (SOI): Angle of Arrival (AOA), Time Difference of Arrival (TDOA) and Power on Arrival (POA).

Each technique has its advantages and disadvantages, successfully locating different signal types with varying degrees of accuracy.

To maximise the performance of the system, Metis Aerospace have developed an integrated solution using the most applicable algorithm based on the type or modulation of the SOI. It can use the sensor type or the sensor network deployment, which is clearly and concisely overlaid onto a terrain map, with RF Spectrum activity. It can also use geolocation performance info, bearing results to the target, along with other sensor info.

The various algorithms are provided as part of the system and can be configured during installation and commissioning. Levels of spectrum activity can then be recorded and stored for playback, evidence and analysis.

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

An overview of the geolocation techniques used 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 receive RF power. Advantages include an 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 uses circular polarised antennas in its design – giving the operator the advantage of maximising the received signal strength from most transmitting signal polarisations. This includes all linear polarization, 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, this allows the tracking of the intersection point and 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 used to skew the EO/IR camera in the same direction to “stare” along that line of bearing at the target. Where a geolocation result is found for the Signal Of Interest, all the systems cameras can be automatically or manually skewed to look at the region where it’s located.

Time Difference of Arrival (TDOA)

Using synchronous time domain captures, TDOA determines the relative time of arrival of a Signal Of Interest at different receiver locations. The technique is optimal for geolocation over wider areas. By utilising three or more synchronised monitoring points, it can more confidently geolocate to a bounded area. TDOA is more successful for wider modulation bandwidths due to the improved signal correlation properties allowing more defined localisation. An important advantage of TDOA 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. It uses synchronous frequency domain captures to determine and compare the instantaneous relative power of a signal at different receiver locations. There is typically 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 a wider area solution.

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