Validity check of vehicle position information

Abstract

A method for validating received positional data in vehicle surveillance applications. A signal carrying a Mode S ES message including positional data indicating an alleged position of a vehicle, transmitted from a radio source is received with a radio direction finding antenna of a receiver. A bearing from the receiver to the radio source is estimated utilizing the radio direction finding antenna and received signal. A distance between the receiver and radio source based on a time of flight for a signal travelling between the receiver and radio source at known speed is estimated with a distance measurer including primary radar, laser detector and ranger, and/or secondary surveillance radar. An estimated position of the radio source is calculated based on the estimated bearing and distance. A deviation value indicating a deviation/coincidence between the alleged position is determined according to the received and estimated position of the radio source.

1 . A method for validating received positional data in vehicle surveillance applications wherein vehicles transmit positional data indicating their own position to surrounding vehicles ( 3 ,  5 ;  5 ′), characterized in comprising the steps of:
 receiving (S 1 ), with a radio direction finding antenna arrangement ( 21 ,  23 ) of a receiving unit ( 3 ), a signal ( 13 ;  13 ′,  13 ″) carrying positional data indicating an alleged position (P ADS-B(5) ; P ADS-B(5′) , P ADS-B(15″) ) of a vehicle, transmitted from a radio source ( 5 ;  5 ′,  15 ″); 
 estimating (S 2 ) the bearing from the receiving unit ( 3 ) to said radio source ( 5 ;  5 ′,  15 ″) utilizing said radio direction finding antenna arrangement ( 21 ,  23 ) and the received signal ( 13 ;  13 ′,  13 ″); 
 estimating (S 3 ) the distance between the receiving unit ( 3 ) and the radio source ( 5 ;  5 ′,  15 ″) based on the time of flight, TOE, for a signal travelling there between at known speed; 
 calculating (S 4 ) an estimated position (P EST(5) ; P EST(5′) , P EST(15″) ) of the radio source ( 5 ;  5 ′,  15 ″) based on the estimated bearing and the estimated distance, and 
 determining (S 5 ) a deviation value indicating the deviation/coincidence between the alleged position (P ADS-B(5) ; P ADS-B(5′) , P ADS-B(15″) ) of a vehicle according to the received positional data and the estimated position (P EST(5) ; P EST(5′) , P EST(15″) ) of the radio source ( 5 ;  5 ′,  15 ″). 
 
     
     
         2 . A method according to  claim 1 , wherein said deviation value is used as an indicator of the reliability of the received positional data. 
     
     
         3 . A method according to  claim 1  or  2 , wherein the signal ( 13 ;  13 ′,  13 ″) carrying the positional data is transmitted using a data link over which a transmission is initiated at a given transmission point in time ( 14 ) that is known by all users of said data link, and wherein the step of estimating (S 3 ) the distance between the receiving unit ( 3 ) and the radio source ( 5 ;  5 ′,  15 ″) is performed by:
 determining the time of flight, TOF, for the signal carrying the positional data based on the time (Δt) elapsed from the transmission point in time ( 14 ) of said signal to the time of reception ( 16 ) of at least a first part of the signal; and 
 estimating said distance based on said TOE and the propagation velocity of said signal ( 13 ;  13 ′,  13 ″). 
 
     
     
         4 . A method according to  claim 3 , wherein the signal ( 13 ;  13 ′,  13 ″) is an ADS-B message ( 13 ;  13 ′,  13 ″) conforming to the VDL Mode 4 format and the data link is a TDMA-based data link, such as a STDMA data link. 
     
     
         5 . A method according to  claim 1  or  2 , wherein the signal ( 13 ;  13 ′,  13 ″) carrying the positional data further comprises transmission time information indicating the point in time at which it was transmitted, and wherein the step of estimating (S 3 ) the distance between the receiving unit ( 3 ) and the radio source ( 5 ;  5 ′,  15 ″) comprises the steps of:
 determining, by using the transmission time information in the received signal ( 13 ;  13 ′,  13 ″), the time elapsed from the point in time at which said signal was transmitted to the point in time at which said signal was received, and estimating said distance based on said determined time and the propagation velocity of said signal ( 13 ;  13 ′,  13 ″). 
 
     
     
         6 . A method according to  claim 5 , wherein said signal ( 13 ;  13 ′,  13 ″) is an ADS-B message ( 13 ;  13 ′,  13 ″) conforming to the UAT format. 
     
     
         7 . A method according to  claim 1  or  2 , wherein the step of estimating (S 3 ) the distance between the receiving unit ( 3 ) and the radio source ( 5 ;  5 ′,  15 ″) is  30  performed by using primary radar equipment ( 19 ,  31 ), laser detection and ranging [LADAR] equipment ( 33 ), and/or secondary surveillance radar equipment ( 19 ,  35 ) comprised in the receiving unit ( 3 ). 
     
     
         8 . A method according to  claim 7 , wherein said signal ( 13 ;  13 ′,  13 ″) is an ADS-B message ( 13 ;  13 ′,  13 ″) conforming to the Mode S ES format. 
     
     
         9 . A vehicle surveillance system ( 17 ) for vehicle surveillance applications wherein vehicles ( 3 ,  5 ;  5 ′) transmit positional data indicating their own position to surrounding vehicles ( 3 ,  5 ;  5 ′), characterized in comprising:
 bearing-estimation means ( 21 ,  23 ) adapted to receive a signal ( 13 ;  13 ′,  13 ″) carrying positional data indicating an alleged position (P ADS-B(5) ; P ADSB(5′) , P ADS-B(15″) ) of a vehicle, transmitted from a radio source ( 5 ;  5 ′,  15 ″), said bearing-estimation means ( 21 ,  23 ) further being adapted to estimate (S 1 ) the bearing to said radio source ( 5 ;  5 ′;  15 ″) using said received signal ( 13 ;  13 ′,  13 ″); 
 distance-estimation means ( 25 ) adapted to estimate (S 2 ) the distance to the radio source ( 5 ;  5 ′,  15 ″) based on the time of flight, TOE, for a signal received there from, which signal travels at known speed; 
 calculating means ( 43 ) adapted to calculate (S 4 ) an estimated position (P EST(5) ; P EST(5′) , P EST(15″) ) of the radio source ( 5 ;  5 ′,  15 ″) based on the estimated bearing and the estimated distance, and 
 comparing means ( 45 ) adapted to determine (S 5 ) a deviation value indicating the deviation/coincidence between the alleged position (P ADS-B(5) ; P ADS-B(5′) , P ADS-B(15″) ) of a vehicle according to the received positional data and the estimated position (P EST(5) ; P EST(5′) , P EST(15″) ) of the radio source ( 5 ;  5 ′,  15 ″). 
 
     
     
         10 . A vehicle surveillance system ( 17 ) according to  claim 9 , further comprising discriminating means ( 47 ) connected to an information module ( 49 ) for informing a system user of surrounding vehicle traffic and/or to a decision and manoeuvring unit ( 51 ) for controlling a vehicle in which the system ( 17 ) is included, said discriminating means ( 47 ) being adapted to discard positional data indicating an alleged position (P ADS-B(5) ; P ADS(5′) , P ADS-B(15″) ) of a vehicle which, according to the deviation value determined by the comparing means ( 45 ), deviates substantially from the estimated position (P EST(5) ; P EST(5′) , P EST(15″) ) of the radio source ( 5 ;  5 ′,  15 ″) from which the positional data was received. 
     
     
         11 . A vehicle surveillance system ( 17 ) according to  claim 9  or  10 , wherein said bearing-estimation means ( 19 ) comprises at least one directional antenna ( 21 ) for receiving the signals ( 13 ;  13 ′,  13 ″) carrying the positional data and a transceiver circuitry ( 23 ) connected to said directional antenna ( 21 ) for estimating the bearing to the radio sources ( 5 ;  5 ′;  15 ″) from which the signals ( 13 ;  13 ′,  13 ″) are received. 
     
     
         12 . A vehicle surveillance system ( 17 ) according to any of the  claims 9  to  11 , wherein said signal ( 13 ;  13 ′,  13 ″) is an ADS-B message ( 13 ;  13 ′,  13 ″). 
     
     
         13 . A vehicle surveillance system ( 17 ) according to any of the  claims 9  to  12 , wherein said vehicle surveillance system ( 17 ) is located in an aircraft ( 3 ) and used in an aircraft surveillance system ( 17 ) for separation provision and/or collision avoidance applications. 
     
     
         14 . A vehicle ( 3 ,  5 ;  3 ,  5 ′), characterized in comprising a vehicle surveillance system ( 17 ) according to any of the  claims 9  to  13 . 
     
     
         15 . A ground-based air traffic control [ATC] station ( 7 ) for air traffic surveillance, characterized in comprising a vehicle surveillance system ( 17 ) according to any of the  claims 9  to  13 .