Precise Positioning for Automotive with Mass Market GNSS Chipsets

Abstract

GNSS chipsets currently in use in automotive applications are typically single frequency receivers offering a code phase solution which does not provide the accuracy required by emerging Advanced Driver Assistance Systems (ADAS), Autonomous Driving (AD), and Vehicle-to-Everything (V2X) applications. Several mass market GNSS receiver manufacturers have recently announced dual frequency chipsets using new civil signals. This paper presents results from using measurements from mass market dual frequency GNSS chipsets in NovAtel’s (a part of Hexagon Positioning Intelligence) Precise Point Positioning (PPP) algorithms to improve the positioning accuracy and integrity to levels suitable for ADAS/AD applications. Data was collected using mass market chipsets from three manufacturers in both static and kinematic scenarios. A zerobaseline static test was performed to characterize the measurement noise of each chipset, with results ranging from 15 to 57 cm for code noise, and 0.7 to 5.3 mm for phase noise, both up to 15x greater than a survey grade receiver. The increased code noise results in increased PPP convergence time. In kinematic testing, under open sky conditions, the horizontal position accuracy ranged from 28 cm to 36 cm at 95%. The use of these measurements in PPP represents an improvement over the code phase position provided by the chipset of 60-90%. Convergence time is a known limitation of PPP algorithms, and is more pronounced with mass market chipsets due to high code measurement noise. Ionospheric corrections from a Regional Ionosphere Model (RIM) are supplied to reduce convergence time. For single frequency mass market chipsets, convergence to 1 metre at 95% is not achieved within 20 minutes without ionospheric corrections. With RIM corrections convergence to 1 metre (95%) can be achieved in less than 30 seconds. For a dual frequency chipset the time to converge to 1 metre (95%) is reduced from 9 minutes to less than 30 seconds. The antenna can also have a significant impact on performance. The convergence performance is compared between a geodetic grade antenna and a representative automotive grade antenna in static moderate multipath environments. In summary, this paper illustrates that measurements from mass market GNSS chipsets may be used with NovAtel’s PPP algorithm and TerraStar-X corrections to achieve the performance demanded by ADAS/AD and V2X applications, and that corrections from a RIM permit convergence times of less than one minute for both single and dual frequency chipsets, a necessary feature for automotive applications.