Study On The Recovery Of Satellite-Based ADS-B Collision Message

ADS-B is the major surveillance technique recommended by International Civil Aviation Organization(ICAO).In order to ensure flight safety,almost all aircrafts are equipped with ADS-B in that some important information such as speed,identity code and location is continuously broadcasted by the ADS-B transmitter.The Air Traffic Management can easily achieve air traffic surveillance and avoid accidents by using the broadcasted information.Due to the small coverage of existing terrestrial stations and great difficulties to deploy in oceans and polar,the terrestrial ADS-B surveillance systems can only monitor some important areas with intensive air traffic.Nowadays,with the increase of air traffic,the current surveillance system is difficult to meet the current needs in the civil aviation safety field.Therefore,the concept of satellite-based ADS-B system is proposed.The integrated deployment cost of satellite-based ADS-B system is low,and relying on the altitude advantage of the satellite,the global airspace surveillance can be realized after the constellation networking is completed.However,compared with the current surveillance system,the coverage of antenna increases geometrically,resulting in a collision of messages.Message collisions may cause errors in the decoded ADS-B information or directly lose some useful information seriously affecting the monitoring of aircrafts.In the project,we focus on the recovery and separation of satellite-based ADS-B collision messages.Firstly,the architecture of the satellite-based ADS-B system is introduced.Then,the format of ADS-B 1090 ES data link signals,and a message collision model based on array reception are studied.For ADS-B messages with different information,the broadcast frequency of airborne ADS-B device is introduced.Considering the influence of source number on signal separation algorithm,two common source number estimation algorithms are introduced.Secondly,for the problem of signal collision,the satellite-based ADS-B system must have the ability to separate the overlapping messages.Therefore,the influences of random interval generated by airborne device on collision probability are analyzed.And a collision probability model of ADS-B messages based on Poisson process is proposed.The study on the collision probability of two and multiple messages ultimately leads to the satellite-based ADS-B system having at least the ability to separate the collision of two or three messages,providing a theoretical basis for the subsequent selection of separation algorithms.Finally,two effective methods to separate mixed signals are studied.Blind Source Separation algorithm is mainly studied based on the model of array receiving signals.The independence of the source signals is used to solve the separation of the mixed signals by solving the de-mixing matrix.Aiming at the collision of two Mode S signals,the PA is studied,and some characteristics of mixed Mode S signals in the time domain are utilized to solve the de-mixing matrix by using singular value decomposition(SVD)mathematical principle and MOORE-PENROSE generalized inverse matrix and other relevant mathematical knowledge,so as to estimate the source signals.The research shows that the above two methods can be used to achieve the separation and recovery of mixed signals.