Resolve complex interference in real time

Many different signal types are potential sources of interference, indicators of illegal activity or unauthorized spectrum use.

Direction finding and individual geolocation techniques are each effective for only a limited range of target signal types, which varies according to many factors including signal bandwidth, modulation, power, background noise, pulse duration and receiver speed.

The most reliable and cost-effective method to ensure detection and successful localization of the maximum range of target signal types is to combine each technique in a single real-time overlay. The RFeye® supports multiple DF and geolocation techniques including Angle of Arrival (AOA), Time Difference of Arrival (TDOA) and Power on Arrival (POA).

TDOA geolocation

Time Difference on Arrival (TDOA) uses the difference in arrival times at receivers to geolocate a transmission using a minimum of three receivers. TDOA works particularly well for pulsed transmissions and can resolve multipath effects; it can be combined with AOA and POA using our Multi Geolocation feature.

TDOA is a well-proven technique that uses synchronous time domain captures to determine the relative time of arrival of a signal at different receiver locations. The technique is optimal for geolocation over wide areas. Two monitoring receiver points will provide geolocation probability in two dimensions (i.e. approximately along a hyperbolic curve), whereas three or more monitoring receiver points will provide geolocation probability to a bounded area or point.

TDOA works best for wider modulation bandwidths with better signal correlation properties and therefore localisation to a narrower area. A significant advantage of TDOA is that the processing gain of correlations allows successful geolocation of signals which are close to, or even below the receiver noise floor. Timing synchronization is required between the receivers for TDOA. For wide area deployments, this is provided most practically by the RFeye on-board GPS receiver. Using RFeye Arrays, TDOA geolocation results are combined with AOA results to provide unrivaled geolocation performance.


Angle Of Arrival (AOA) is a geolocation technique which triangulates location using two or more Lines Of Bearing (LOB) generated from direction finding techniques. Where many LOB are available, quality thresholding allows these to be used selectively, removing poor quality multipath affected signals to maximise geolocation accuracy.

Two or more LOB can be generated using a fixed network of two or more antenna arrays. Alternatively, a single mobile antenna array (using a Direction Finding Vehicle) can pinpoint location with our Cumulative Tracking feature.


Power On Arrival (POA) is a geolocation technique which uses the differences in power at receivers to pinpoint location using a minimum of three receivers. POA is particularly useful for short range applications such as in buildings and RFeye SyncLinc can further improve in-building performance by time-synchronizing receivers very accurately.

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 drop-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 accurate timing synchronisation between receivers. Although GPS synchronisation is viable, it is typically not practical or secure for in-building applications. High performance wired timing synchronisation systems such as RFeye SyncLinc are therefore used in-building.


CRFS has developed an enhanced TDOA technology that can provide accurate geolocation of emitters in three dimensions using a ground-based network of nodes. This network can passively track multiple ground-based and airborne transmitters, including aircraft and UAVs, in real time to provide latitude, longitude, altitude and speed data.

Our 3D TDOA solution delivers excellent accuracy; we have demonstrated passive tracking of aircraft with errors as low as a few hundred meters over a range of hundreds of kilometers and 10 km altitude. Over smaller ranges, tracking accuracy of tens of meters is feasible.

Flight paths generated from 3D TDOA results can be viewed in the mapping tools of our state-of-the-art RFeye Site software, as well as being exported for overlay in Google Earth. Our 3D TDOA software is a plugin to RFeye software, which enables a network of RFeye Nodes to be used to track airborne emitters. The same Nodes can be simultaneously used for other spectrum monitoring and management missions. To provide emitter geolocation in three dimensions, a minimum of four RFeye Nodes is needed.

The system can operate as a stand-alone emitter tracking system or as part of a broader UAV / airborne threat detection and defense system encompassing optical, radar, and countermeasure capabilities.

Geolocation continued…

RFeye software enables multiple simultaneous geolocations to be performed on multiple target frequencies. The software outputs geolocation results as POA and TDOA probability heat maps and overlays real-time AOA vectors onto map interfaces. When combined with the 3D topographical displays and the additional user-defined data layers that can be input via import wizards, this visualisation of the geolocation results provides an unrivalled means of tracking signal source in real time. Multiple results can be overlaid simultaneously onto the map for ease of visualisation and analysis.

The mapping tools include full zoom facility and ability to display many simultaneous maps, with Shuttle Radar Topography Mission (SRTM) data overlay available to aid geolocation analysis.

RFeye software supports several different map formats (OpenStreetMaps, MapQuest or custom tiles), satellite imagery (ESRI, MapQuest Aerial, GeoStage or custom tiles) and SRTM elevation data. These data sets can be Alpha blended and overlaid on top of one another to give the best possible view of the terrain and structures. Additional custom graphical data can be overlaid on the map windows in Shape and GeoTiff file formats Geolocation processor modules are included for Time Difference of Arrival (TDOA), Angle of Arrival (AOA) and Power on Arrival (POA) geolocation.

The software can also be used in a powerful simulation mode allowing for the geolocation and real-time monitoring functionality of RFeye software to be tested with simulated Nodes. RFeye software includes the modelling capability to detect and geolocate different signal types taking account the sensitivity, density and positioning of receiver Nodes. Detailed settings are available to specify receiver and transmitter parameters maximising real-world correspondence. Example receiver settings include noise figure, antenna gain and sweep rate while transmitter parameters include modulation type, constellation rotations and the ability to define pulsed and frequency hopping signals. Trajectories can also be added to simulate non-stationary transmitters and receivers.

Check out videos of our simulation and modelling software here

An optional Propagation Analysis module is available for modelling optimal receiver positioning and other scenarios in a given location taking account actual terrain, customer-defined building structures, and Fresnel diffraction.