Low complex and stable EKF for Mass Market Dual Frequency Receivers

Abstract

Even though the remarkable growth of the last years, the global GNSS market will still continue to expand in the next decade both in terms of devices and service. The introduction of a new generation of mass market chips based on multi GNSS dual frequency measurements, already being commercialized and integrated in smartphones by major manufacturers, is contributing to a new level of positioning accuracy in the mass-market location-based services. Better positioning and navigation experience in urban environments are the key challenges of dual-frequency GNSS enabled receivers. Thanks to the shape of the E5 signal provided by Galileo satellites as well as the other wide-band signals available on the same band, as provided by GPS satellites, the multipath effect could be greatly reduced with significant improvement on the position accuracy. In this paper a low complexity uncombined dual frequency Extended Kalman Filter (EKF) filter is presented. The goal is to deliver continuous and smooth navigation results, even in challenging environment conditions, with a low complexity and stable solution for the GNSS mass market. The proposed EKF follows the standard and simple approach of the single frequency EKF, but exploiting the measurements from both L1 and L5 bands to take benefits of the straightness of L5 measurements against multipath. Therefore, a simple uncombined L1 and L5 measurements approach is used and it is preferred in area with not significant ionospheric error. For each epoch and for each satellite in view, only the measurements coming from one frequency are selected. To exploit the resilience of L5/E5a measurements against multipath and to overcome the visibility limitation due to lower number of satellites available on L5 band than on L1 band, a “visibility check” on the measurements available is done. To show the greater resistance of L5/E5a measurements to the effects of multipath and so to test the proposed EKF, the raw measurements of a mass market dual frequency chipset for smartphone of two kinematic data collections are used. To cover different signal reception conditions, an urban/sub-urban and a rural environment are chosen. Different PVT post processing configurations have been applied to the GNSS observations, to evaluate the impact of carrier phase pseudorange smoothing and of the different frequency selections on the position accuracy and solution availability. In addition, the performance of the proposed standard single point positioning EKF using uncombined dual frequency signals is also compared to the performance obtained by processing the same raw measurements with an external Precise Point Positioning (PPP) tool. The results are promising and show that a positioning improvement from few meters up to tens meters is possible using dual frequency mass market receivers with respect to single frequency receivers, both in mild and harsh environments.