Low-cost, triple-frequency multi-GNSS PPP and MEMS IMU integration for continuous navigation in urban environments

Precise and continuous positioning and navigation in urban areas can be achieved using high performance and expensive GNSS and IMU technology. However, modern applications demand higher accuracy and precision using much lower-cost sensors. In this research, next-generation, low-cost multi-frequency GNSS, microelectromechanical (MEMS) based Inertial Measurement Unit (IMU), and a patch antenna was used to obtain decimetre level accuracy in a suburban and urban environment. To compensate for the low-cost GNSS hardware errors, Precise Point Positioning (PPP) augmentation, ionosphere constraining (IC) and the third frequency of GNSS were included while vehicle constraining/ Non- holonomic constraints (NHC) were used on MEMS IMU measurements. A unique combination of the low-cost hardware and software constraining was used to bridge the GNSS gaps in an urban environment to provide a continuous, accurate, and reliable position solution that is novel and has not been explored and published earlier. In the past, high-precision, dual-frequency (DF) GNSS PPP + IMU and low-cost, single-frequency (SF) GNSS PPP + IMU were examined and analysed in the PPP + IMU research area. The accuracy performance of the TF PPP + IMU with constraining algorithm was tested rigorously using various combinations of satellites such as individual constellations and a combination of constellations during the introduced GNSS outages. TF PPP and IMU demonstrates less than a decimetre-level accuracy in the presence of a sufficient number of satellites. During 30 seconds of introduced GNSS signal loss, the overall rms of TF GNSS PPP + IMU + IC algorithm is 10-40% better than DF GNSS PPP + IMU, as the number of satellites available reduces progressively from 4 to 1. The addition of IC and NHC helps in improving the accuracy of the positioning solution during reconvergence after an outage. The decimetre level accuracy results obtained during partial GNSS availability indicate a significant step forward in the low-cost navigation area for applications such as low-cost autonomous vehicles, intelligent transportation systems, UAVs., etc. that demand a decimetre level of accuracy in all environments.