Superbus Positioning System

Abstract

In this report a high accuracy positioning system is investigated for use in the Superbus. The Superbus project is an effort to apply a new and complete conceptual approach to public transport. It consists of a vehicle, logistics and infrastructure. The positioning system for the vehicle is to have a horizontal position error, which will not exceed 5 cm in 95% of the obtained solutions. Secondary requirements included large (quasi-national) deployment area. Networked RTK positioning using GPS is shown to be a valid means to adhere to these requirements. Real Time kinematic (RTK) positioning allows for the required accuracy, while a base station network will allow for the required deployment area using Pseudo Reference Stations (PRS). UMTS is shown to be potentially effective for the required wireless data transfer using the NTRIP protocol. Testing con?rmed adherence of the Superbus Positioning System to the requirements in a variety of real world scenarios. Furthermore, the receiver is shown to perform to manufacturer speci?cations. Dif?cult environmental conditions, such as urban areas and multipath are con?rmed to have an effect on the position estimate in certain situations. It is however demonstrated that the receiver is capable of adhering to Superbus requirements in these situations, provided the initial ambiguity resolution is correct. Temporary signal loss of all satellites (for example due to an underpass) is shown to in?ict the need to reinitialise the ambiguity resolution algorithm, causing a temporary unavailability (around 20 seconds) of the precise RTK position estimate. Heading estimates are also established to be within speci?cations in good conditions. In high multipath conditions, or conditions with a low amount of satellites in view, the heading estimates exceed the manufacturing speci?cations with varying margins. This is possibly due to the fact that the ambiguities of the secondary antenna cannot be ?xed in this scenario. Material testing showed that carbon ?bre, the material that initially would cover the antennas in the vehicle, is highly un?t for this purpose. A thermoplastic counterpart shows no degradation of the satellite signal, and can be used for said purpose.