1090 MHz ADS-B-Based Wide Area Multilateration System for Alternative Positioning Navigation and Timing

The use of the automatic dependent surveillance-broadcast (ADS-B) as a source of alternative positioning, navigation, and timing is attractive as the system has been or soon will be fielded. In this study, a wide-area multilateration (WAM) testbed was developed that implements a time difference of arrival (TDOA) positioning algorithm using the 1090 MHz ADS-B Mode S ES signal in the Taiwan area. The positioning performance of the TDOA-based WAM is influenced by the geometric distribution of ground stations. Common requirements for terrestrial navigation systems target nominal horizontal dilution of precision (HDOP) of 2.828 or lower to support aviation navigation and surveillance [1]-[7]. Meeting such a requirement would necessitate a significant and geometrically diverse number of stations which limits the WAM implementation in countries with limited real estate. It also makes implementation expensive in general. Provided the measurements have adequate accuracy, it is still possible to meet position accuracy targets without such a geometry requirement. However, reducing geometry requirements presents issues with regards to developing a reliable and accurate position solution. This paper proposes a reasonable means of providing an accurate solution given limited station availability and demonstrates the concept in a testbed system implemented in Taiwan. In order to provide more reliable solution, a positioning algorithm is proposed that combines iterative and non-iterative methods to provide reliable convergence to the near optimal solution given the available measurements and the addition of barometric altitude from ADS-B to improve geometry. Importantly, the paper demonstrates positioning performance that meets the requirements for aviation navigation and surveillance services collected with actual flight data and the developed WAM.