Peter F. de Bakker

Short and zero baseline analysis of GPS L1 C/A, L5Q, GIOVE E1B, and E5aQ signals

Stochastic properties of GNSS range measurements can accurately be estimated using a geometry-free short and zero baseline analysis method. This method is now applied to dual-frequency measurements from a new field campaign. Results are presented for the new GPS L5Q and GIOVE E5aQ wideband signals, in addition to the GPS L1 C/A and GIOVE E1B signals. As expected, the results clearly show the high precision of the new signals, but they also show, rather unexpectedly, significant, slowly changing variations in the pseudorange code measurements that are probably a result of strong multipath interference on the data. Carrier phase measurement noise is assessed on both frequencies, and finally successful mixed GPS-GIOVE double difference ambiguity resolution is demonstrated.

Lane Determination With GPS Precise Point Positioning

Modern intelligent transport solutions can achieve an improvement of traffic flow on motorways. With lane-specific measurements and lane-specific control, more measures are possible. Single frequency precise point positioning (PPP) is a newly developed and affordable technique to achieve an improved position accuracy compared with global positioning system (GPS) standalone positioning. GPS-PPP allows for sub-meter accurate positioning, in real time, of vehicles on a motorway. This paper tests this technique in real life; moreover, it presents a methodology to map the lanes on a motorway using data collected by this technique. The methodology exploits the high accuracy and the fact that the most driving is within a lane. In a field test, a GPS-PPP equipped vehicle drives a specific motorway stretch 100 times, for which the GPS-PPP trajectory data are collected. Using these data, the positions and the widths of different lanes are successfully estimated. Comparison with the ground truth shows a dm accuracy. With the parametrized lanes, vehicles can be tracked down to a lane with the GPS-PPP device.

Real-time multi-GNSS single-frequency precise point positioning

Precise Point Positioning (PPP) is a popular Global Positioning System (GPS) processing strategy, thanks to its high precision without requiring additional GPS infrastructure. Single-Frequency PPP (SF-PPP) takes this one step further by no longer relying on expensive dual-frequency GPS receivers, while maintaining a relatively high positioning accuracy. The use of GPS-only SF-PPP for lane identification and mapping on a motorway has previously been demonstrated successfully. However, the performance was shown to depend strongly on the number of available satellites, limiting the application of SF-PPP to relatively open areas. We investigate whether the applicability can be extended by moving from using only GPS to using multiple Global Navigation Satellite Systems (GNSS). Next to GPS, the Russian GLONASS system is at present the only fully functional GNSS and was selected for this reason. We introduce our approach to multi-GNSS SF-PPP and demonstrate its performance by means of several experiments. Results show that multi-GNSS SF-PPP indeed outperforms GPS-only SF-PPP in particular in case of reduced sky visibility.

Mitigation of Ionospheric Delay in GPS/BDS Single Frequency PPP: Assessment and Application

Single-frequency (SF) Precise Point Positioning (PPP) is a promising technique for real-time positioning and navigation at sub-meter (about 0.5 m) accuracy level because of its convenience and low cost. With satellite orbit and clock error being greatly mitigated by the precise products from the International GNSS Service (IGS), ionospheric delay becomes the bottleneck of SF PPP users. There are five commonly used approaches to mitigate ionospheric delay in SF PPP: (1) broadcast ionospheric model in Global Navigation Satellite System (GNSS) navigation message; (2) global ionospheric map released by the IGS; (3) local ionospheric model generated using GNSS data from surrounding reference stations; (4) satellite based ionospheric model; (5) the parameter estimation method. Those approaches are briefly reviewed in our contribution and the performances of some classical ionospheric approaches for SF PPP are validated and compared using GPS data from two networks in China and the Netherlands respectively. Validation results show that a set of reference stations is critical for SF PPP with sub-meter positioning accuracy, especially in China. It is better to model the ionospheric delay in a satellite by satellite mode rather than an integral mode under the assumption of a thin-layer ionosphere. Comparing to GIM, the suggested approach, satellite based ionospheric model (SIM), can improve the horizontal positioning accuracy of SF PPP from 0.40 to 0.10 m in China and from 0.20 to 0.05 m in the Netherlands, while it can improve the vertical accuracy from 0.70 to 0.15 m (China) and from 0.20 to 0.10 m (the Netherlands). Furthermore, the recommended ionospheric model has been applied to GPS/BDS data for SF PPP as well. The experiment in Beijing shows that the positioning of about 0.5 m accuracy can be achieved by single epoch SF PPP based on a reference network of about 40 km inter-station distance. The accuracy of SF PPP based on an accumulation of 10–15 min of observations in dynamic mode is about 0.04 m (horizontal) and 0.04–0.08 m (vertical) using only GPS data, while it is about 0.03 m (horizontal) and 0.03–0.06 m (vertical) by combining GPS and BDS data.

Obtaining real-time sub-meter accuracy using a low cost GNSS device

Autonomous vehicles require accurate position at all times in different environments at an affordable price. This accurate position can only be achieved when combining multiple positioning methods. One of these methods is presented in this paper: positioning based on a Global Navigation Satellite System (GNSS) to obtain absolute position. This solution should be at an affordable price with sub-meter position accuracy. At the University of Delft, the Netherlands, a low cost solution was developed in Matlab for open areas which is called Single Frequency Precise Point Positioning (SF-PPP). It uses a low cost receiver with single frequency, single antenna and single GNSS constellation (GPS). The receiver provides raw measurements to the SF-PPP algorithm which corrects them for different kind of errors. This method was ported to a low cost Commercial Off-The-Shelf (COTS) embedded platform in C++. The selected platform is a Raspberry Pi version 2 with a u-Blox NEO 7P GPS receiver. The corrections for the raw measurements are received from a network service via a 4G modem. The PPP method is validated with an RTK system which is cm accurate. We evaluated the PPP method in different environments and conditions, with focus on open area, but also for harsh conditions on the highway and in an urban environment to know the current limitations of the method. For the open area environment a horizontal root mean square error (RMSe) of 0.5 m on position coordinates was achieved which fulfills our target of submeter accuracy. In harsh environments we suffer from reflections (caused by multipath receptions) and poor satellite availability due to obstructions from trees and buildings which makes the accuracy varying from 0.5 m up to 3 m. Future plans to improve the results involve using more satellites from other constellations like GLONASS, using the Doppler shift to estimate the vehicle speed, using dual frequency receiver for ionosphere removal and closer integration with other low-cost sensors and vehicle model.