BDS/AeroMACS Integrated Positioning Algorithm for Airport Surface Surveillance
Wang Zhipeng, Gao Zhen, Du Jingtian, Zhu Yanbo, Beihang University, China
Location: Bayview Ballroom 1
By the end of 2018, Beidou 3 has completed the basic system construction and started to provide open and authorized services worldwide. Aeronautical Mobile Airport Communications System (AeroMACS) is a new generation of airport broadband communication system recommended by the International Telecommunication Union (ITU). AeroMACS can guarantee the transmission and acquisition of various information among airport ground equipments, which meets the increasing traffic volume of large airports.
The combination of Beidou and AeroMACS can achieve high-precision positioning and monitoring and real-time data wireless transmission within the airport surface. At present, China has successfully implemented airport surface surveillance applications based on AeroMACS and Beidou. At Hehua Airport, the current position and speed information of vehicles are obtained through the Beidou high-precision positioning system, and AeroMACS network in the tower monitors the aircraft and vehicle operation situation in the airport surface, so as to realize the real-time monitoring of complex activities and acquire the efficient and safe operation of the airport surface. However, the satellite signals may be obscured by the Tian-men mountain located in back of the Hehua Airport, which causes the unavailability of Beidou system. It will be difficult to realize the high-precision positioning within the airport surface. Therefore, it is necessary to study the airport surface surveillance method of Beidou and AeroMACS in complex environment.
The main contents of this paper are as follows:
Firstly, aiming at the situation that the Beidou is not available due to the decrease of visible satellites in the complex airport scene environment, the method of Beidou and AeroMACS integrated positioning algorithm is proposed. AeroMACS not only is responsible for ground wireless communication, but also can be used as an auxiliary positioning means. With the surface vehicle as the pseudo satellite, AeroMACS is responsible for the communication between the vehicles and the aircraft. And it provides the three-dimensional position and velocity of the neighboring vehicles for the target aircraft. The target aircraft measures the frequency of the received signal of AeroMACS , and the ground pseudo range rate is calculated by the Doppler frequency shift technique. The observed satellite pseudorange value and the ground pseudorange rate are fused as the observation data. The current state value of the aircraft is predicted by employing an one-step transition probability matrix of the known state value at the previous moment. Using the state values and observation datas, we can get the final positioning result by employing the Kalman filtering algorithm.
Secondly, fault detection needs to be performed after obtaining the combined positioning results. For the BDS/AeroMACS integrated positioning system, this article chooses the innovation value of Kalman Filtering as the test statistic and employs the chi-square test to detect the fault of the integrated positioning system. The threshold is obtained through the known false alarm rate that is pre-allocated to the combined positioning by system. Comparing the test statistics with the threshold value, we can judge whether there is a fault and the positioning result is refused. If the innovation value of the combined positioning is greater than the threshold value, we think that there is a fault in the combined positioning system and the positioning result is unreliable. At this moment, we can use the solution separation algorithm to detect and eliminate the satellite pseudo range of BDS and pseudo-range ratio of AeroMACS.
Finally, the influence of the deviation caused by satellite fault on the final positioning result is analyzed. Because AeroMACS is reliable as a special communication means for airport, only a small proportion of the integrity risk value (0.75 ×1e-6) is allocated to AeroMACS. Therefore, this paper analyses the influence of Beidou satellite fault on positioning error. The Kalman filter algorithm will cause the fault deviation of Beidou to be transmitted during the whole filtering process, which will affect the final positioning error and its envelope (the envelope of positioning error is the protection level of the combined positioning system). On the premise of Beidou satellite fault, the expression of Kalman filter state error is deduced, and the protection level of the combined positioning algorithm is calculated according to the pre-allocated integrity risk value. The error envelope under the condition of satellite fault is obtained, and the performance of the combined positioning can be evaluated.
The method of airport surface surveillance based on Beidou and AeroMACS integrated positioning can effectively solve the problem of vehicle and aircraft positioning in the area of airport surface when Beidou is unavailable. Moreover, the combined positioning algorithm based on Kalman filter will update the state value of the system once a set of new measurement value is obtained, which finally make the state value has the smallest mean square error. And the errors are all in the envelope of protection level. AeroMACS, as a special communication means for airports, has high stability, fast transmission rate and can combine with Beidou navigation system with high feasibility. Therefore, the combination of AeroMACS and Beidou navigation technology can achieve high-precision navigation positioning and scene monitoring, and real-time data wireless transmission within the airport without other hardware facilities.