European GNSS Independent ATM Surveillance Satellite Constellation

Description:

The present method supports ESA’s plans to initiate a European satellite-based GNSS-independent cooperative surveillance system in order to provide a higher level of resiliency and security to protect a basic pillar of Air Traffic Management that is the air traffic surveillance.

The GNSS independence distinguishes the proposed solution from the Automatic Dependent Surveillance-Broadcast (ADS-B) which is reporting the aircraft position based on the GNSS information. It uses uses MODE-S squitter radio signals that are recurrently transmitted by the aircraft and which contain a static 24-bit aircraft unique identifier (known as ICAO aircraft address) and other known bits (such as parity bits for the static address). This static content of the MODE-S signals is particularly important as it allows (satellite) receivers to significantly improve the signal detection as well as timing and carrier frequency estimation of the incoming signal, hence improving the accuracy of post-processing algorithms for geo-locating the aircraft. 

The aircraft position is computed in real-time by applying known techniques such as multi-lateration techniques relying on Time difference of arrival (TDOA) or Frequency difference of Arrival (FDOA). Multiple satellites will receive each aircraft MODES-S squitter (broadcasting) signals either with some time delays or with relevant frequency difference due to Doppler, proportional to the distance of aircraft from each satellite, making it possible to calculate aircraft position geometrically, simply based on the difference in the time of arrival or the frequency Doppler shift of the signal received by multiple satellites. 

In order to determine the position of the aircraft, at least four independent observations of the same MODE-S signal is required. However, a higher number of observations (if available) can be used to improve the accuracy of the position and resolve the dilution of precision caused by the geometrical location of satellites with respect to the target aircraft. 

The proposed method implies that captured signals will need to be further processed either on-board or on ground to extract the 24-bit ICAO aircraft identifier that is uniquely associated to each aircraft; this is the only necessary information required to identify the aircraft position (additional information such as extended squitter could also be used to further enhance the performance optionally). 

It does not require any external intervention or interrogation of the aircraft which means that  there is no need to change the existing MODE-S transmitting signal format. This is of paramount importance as no additional equipment on board of the aircraft or any change in the operation procedures are required. 

Figure 1 below shows a conceptual implementation of this method for air traffic surveillance where broadcasting MODE-S signals are passively detected by multiple satellite simultaneously (no interrogation needed from the space segment).

• Pan-European deployment at once.
• Cost-efficient.
   o Air wise: No need for extra & costly avionics
   o Ground wise: Re-use of existing assets and Air Navigation Service Providers surveillance applications.
   o Space wise: Re-use of existing secure ground infrastructures. Hosted-payload solutions. Option to use satellite redundancy as opposed to costly space qualified components.
• Spectrum-efficient.
   o Passive system - contributes to reduction of spectrum congestion.
   o No interferences generated
• Fully interoperable with existing ground infrastructure.
• European-wide approach for service provision.
• Potential for a worldwide service

Domain of application:

The invention concerns air traffic surveillance with a space based approach which will provide a cost-effective solution especially not only for areas where no alternative terrestrial solution exists but also in continental areas with high traffic density where the use of secondary radars for surveillance is becoming cumbersome due to over interrogations which often saturate aircrafts transponders.

IP Status

An International patent application (PCT) has been filed.