An Analysis of Positioning Method in AIS Ranging Mode

Abstract

Position, navigation and timing (PNT) resiliency is required in e-Navigation strategy, which is proposed by International Maritime Organization (IMO). The PNT is mainly provided by global navigation satellite system (GNSS) at sea for now. It is necessary to introduce an alternative position system using a different technique, as a complement to existing GNSS. The automatic identification system (AIS) is utilized far and wide for collision avoidance based on radio-communications at sea and is mandated by IMO. However, position information of AIS depends on GNSS currently. If AIS can estimate the position by itself independently of GNSS, it would be of great significance to ensure resilient PNT. AIS base stations transmit the ranging signals, while vessels monitor the signals and then calculate the position. This idea is called AIS ranging-mode (R-mode) in e-Navigation. AIS R-mode positioning system is a potential candidate system to resilient PNT in the World Wide Radio Navigation System (WWRNS). This paper focuses on positioning methods used in AIS R-mode. Two position estimation methods are investigated. One is a direct positioning method according to geodetic surveying. The other is a positioning method according to map projecting. Principles and mathematical models of these methods are presented respectively. Besides the theoretical analysis, the performance of these two positioning methods using in AIS R-mode is also evaluated by simulation both with the ideal condition and with the additional secondary factor (ASF).