2WAM/MLAT AlgorithmWAM algorithm is a hyperbolic positioning algorithm, the basic equation shown at right. If the number of base stations over four, the basic equation for thesuper-set equation to convert non-overdetermined equation by the least squares method.
3WAM/MLAT AlgorithmTheoretical derivation can be drawn, multi-point positioning precision and accuracy of time difference relationship for the approximate linear relation, matrix G directly influences the positioning precision, while the matrix G by the site location and positioning point position is decided jointly. According to GPS positioning theory, can introduce HDOP / VDOP factor to describe the MLAT/WAM error distribution. According to statistics, ultimately need to get 95% confidence level error, can be expressed as: EPU = 1.96HDOP δ
4TEDC WAM/MLATTEDC ADSB-2000A provides two types of Multilateration model:WAM mode used for time synchronization methods, through the GPS ( the future use of the COMPASS) time, by base stations (time synchronization accuracy needs to be controlled within 100ns ).Surface monitoring Multilateration using independent transmitter with high precision timing, the TEDC ADSB-2000A device can provide the highest 1ns timing precision (theoretical value of up to 0.3 meters), taking into account the crystal temperature drift, base station position measurement error, baseband pulse measurement and other reasons, the system in the best condition base station layout, the design accuracy requirements for RMS 10 metres.
6TEDC WAMTEDC WAM based on TEDC ADSB-2000A receiver equipment R & D, consists of the following components:The ADSB-2000A receiver (3 above )10W 1090ES transmitterCentral processing computerData output interface deviceThe optional 1030MHz rotary inquiry machine
7TEDC WAMTEDC has carried on many times the multilateration test, the car station in Beijing Daxing District, Hebei Xiongxian, Hebei Cangzhou, Hebei Dingzhou built four remote multilateration station.Test contains the 1090MHz ModeS, Mode A / C and ADS-B ( out ) frame .
11ADS-B Security ADS-B data security is the basic problem: Air Ground transmission reliability ( transmission delay, crosstalk, interweaves wait for a problem )False target and electronic jamming.GNSS system integrity loss / failure and ADS-B Out alternative surveillance technology.
16ADS-B Security ADS-B data security problems: ADS-B data reliability. ATC system’s fusion model.ADS-B data transmission and usability problems.
17ADS-B Security ADS-B data reliability problems Airborne ADS-B apparatus is provided to position the confidence degree ( NUCp ) may not be entirely reliable, different aircraft in the same region of the same moment may have a different location confidence value.As a result of airborne equipment and firing pattern of inconsistency, leading to ADS-B position data is not accurate
18ADS-B SecurityFrom the statistics, NUCp value mainly concentrated in the5,6,7, but a large proportion of the data NUCp 0, NUCp 0means that the ADS-B position data is invalid.
19ADS-B Security ATC system security issues (for processing ADS-B data) Unproven ADS-B track directly into the automated system position accuracy and transmission delay of dual risk.Position risk is airborne equipment NUCp inconsistency, may lead to some lost tracks, or to produce incorrect track.Transmission delay will lead to automatic velocity tracking system instability condition, serious cases will affect the tracking accuracy.
20ADS-B SecurityExtended ADS-B ground station, through the regional centralized processing can solve the ADS-B security problems.ADS-B ground station should provide precise timing function, the use of precision timing, without changing the construction scale of the circumstances, can greatly improve the security questions of ADS-B data.Regional centralized processing is the current ADS-B construction is necessary and urgent problem, through the regional centralized treatment, can improve the ADS-B ground station network capacity, and provides additional functionality.