Research And Implementation On Target Tracking Technology Of Collision Avoidance System

Safety is the eternal theme of aviation. In order to ensure the flight safety, we must be well acquainted with the flight status information of those aircraft within a certain distance, including position, speed, the expected track etc., which are the basis for us to judge and adjust the aircraft’s flight status for the sake of ensuring safety. Air Traffic Control(ATC), a system running on ground but controlling the traffic situation in the sky,cannot absolutely guarantee safety of the aircraft. While Traffic Collision Avoidance System(TCAS), which is a backup of ATC system to avoid collision among aircraft,can work independently to monitor and track nearby aircraft and then submit collision avoidance resolution to the pilot. CAS is the core subsystem of TCAS, and its mission is to provide tracking function and collision avoidance resolution. The performance of CAS is a decisive factor for flight safety. Therefore, this paper mainly focuses on the target tracking system of the CAS subsystem.Tracking the surrounding aircraft needs to be done within the three dimensional space. Considering the difference between vertical and horizontal measuring methods used by TCAS, this paper will design and implement target tracker from vertical and horizontal directions respectively:In vertical direction, TCAS has two different accuracy altitude reports:25ft and100 ft. For the 25 ft accuracy measurement, - filter can be used; while for the 100 ft,the - filter is not suitable because it will lead to unacceptable tracking error. For this reason, this paper designs a nonlinear altitude tracker which is used to calculate the altitude rate. In fact, a so-called altitude rate is the ratio of time that is a cost for aircraft to traverse different altitude and the layers of the altitude. According to the altitude rate,altitude can be reflected indirectly. Simultaneously, the flight process is divided into five states, and each of them uses different correction formulas to revise the altitude rate. Both the simulation results and error analysis demonstrate that the nonlinear altitude tracker is much better than - tracker. It shows that the nonlinear altitude tracker improves the tracking precision, reduces the response time and provides much more reliable consultant for TCAS to make collision avoidance resolution.In horizontal direction, - filter and Kalman filter are two mainly used trackers. In horizontal direction, aircraft may have complex maneuvering, therefore, the paper designs three independent trackers: Cartesian tracker, Parabolic tracker and Range Bearing tracker. Each tracker has its own function and application conditions. Combining the three trackers’ tracking results and the flight mathematical model, we can detect maneuvering and track timely. Simulation results demonstrate the horizontal tracker can satisfy the requirements of TCAS minimum performance standards in both tracking accruacy and maneruvering tracking.In order to test the tracking system conveniently and visually, this paper provides a visual simulation platform which is developed Matlab GUI. The tracking system comes through the test with the standard test cases listed in TCAS and the result shows that tracking system achieve the performance requirements of the CAS subsystem and can be applied to engineering practice.