DME-Aided Multilateration for GNSS Backup Surveillance
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Solution Overview
Problem
Existing GNSS-based surveillance systems are vulnerable to disruptions from solar storms and intentional/unintentional interference, leading to degradation or loss of aircraft position information, necessitating a backup or augmentation system for reliable ground surveillance in the National Airspace System.
Innovation Solution
The integration of DME listener units with existing DME ground stations to provide DME-aided multilateration, utilizing DME interrogators and transponders to determine time differences of arrival (TDOA) and aircraft positions through cross-correlation of interrogation and reply pulses, with central computers processing this data to determine precise aircraft locations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If GNSS-based surveillance systems are used for ground surveillance, then position information can be obtained, but the system becomes vulnerable to disruptions from solar storms and intentional/unintentional interference
Solution Approach 1:
The patent converts the limitation of DME systems (inability to provide direct position information) into a benefit by using the existing DME infrastructure for multilateration. The harmful vulnerability to GNSS interference is transformed into an opportunity to use a completely different measurement principle (time difference of arrival of DME signals) that is immune to GNSS-based interference, thereby achieving surveillance availability when GNSS is disrupted.
Solution Approach 2:
The patent changes the fundamental measurement parameter from GNSS satellite signal reception to DME signal time difference of arrival measurement. By measuring TDOA of DME interrogation and reply signals between multiple ground stations and the aircraft, the system achieves position determination through a completely different physical parameter that is not affected by GNSS interference or solar storms.
2Measurement precision
If DME listener units are added to existing DME ground stations for multilateration, then position determination capability is provided, but the device complexity increases
Solution Approach 1:
The patent makes existing DME ground stations multi-functional by adding listener units that enable them to perform not only their original DME transponder function but also multilateration measurement function. The same ground station infrastructure provides both traditional DME range information and TDOA-based position information, eliminating the need for completely separate surveillance infrastructure.
Solution Approach 2:
The DME listener units at ground stations automatically capture and process DME interrogation and reply signals without requiring additional active transmission or complex processing. The system uses the existing DME signal exchange between aircraft and ground transponders to derive position information, making the ground stations self-sufficient for both traditional and multilateration functions.
3Object-generated harmful factors
If DME channels overlapping with SSR frequencies are reserved for SSR, then co-channel interference is minimized, but the quantity of available DME channels decreases
Solution Approach 1:
The patent uses signal processing and correlation techniques as intermediaries to distinguish between DME and SSR signals. By capturing both DME interrogation and reply signals and processing them through correlation algorithms, the system can identify and measure TDOA even when DME channels overlap with SSR frequencies, effectively mediating the co-channel interference problem.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution provides a reliable ground surveillance capability that complements GNSS systems, enhancing position determination accuracy and availability by leveraging existing DME infrastructure, even during disruptions, and reduces the need for additional ground stations.
Implementation Method 1
providing at least one DME listener for receiving and demodulating the interrogation pulses transmitted by the at least one DME interrogator and the reply pulses transmitted by the at least one DME transponder
Implementation Method 2
cross correlating the received interrogation pulses and reply pulses and determining a cross correlation output, determining an interrogation pattern of the received interrogation pulses and reply pulses by selecting overlapping pulses of the received interrogation pulses and reply pulses when a maximum peak of cross correlation occurs
Data Source
AI summary
The present invention utilizes the existing DME transponder system infrastructure to augment existing ground surveillance multilateration (MLAT) capabilities by providing additional measurements for determining the position of an aircraft equipped with a DME transponder. DME listeners receive DME interrogation signals and DME reply signals, determine TDOA between the DME transponder and each DME listener, and transmit data to a central computer that clusters TDOAs between the DME transponder and the DME listeners and computes the aircraft position using the clustered TDOAs. The DME-aided MLAT can be used as a backup surveillance system when GNSS-based systems are unavailable. The DME-aided MLAT can be integrated with SSR receive units (RUs) performing multilateration (MLAT) calculations.