A GNSS/Barometric Altimeter Tightly Coupled Integration for Three-Dimensional Semi-Indoor Mapping With Android Smartphones

This letter introduces a GNSS/altimeter tightly coupled (TC) integration algorithm that combines barometric altitude measurements with GNSS observations to determine 3-D positions. By transforming barometric altitude measurements into Earth-centered Earth-fixed (ECEF) coordinates, a novel TC integration equation is derived. This equation enables accurate positioning with only three GNSS satellites and one altitude measurement, overcoming the limitations of conventional GNSS positioning techniques. A semi-indoor experiment for various smartphones was conducted to validate the proposed method, comparing it against conventional positioning techniques and the National Marine Electronics Association (NMEA) location provided by smartphone chipsets. The results demonstrated that the GNSS/BARO TC integration significantly reduced errors and improved accuracy. Notably, the mean error of 4.74 m horizontally and 2.43 m vertically improved the NMEA results by 63.31% and 89.18%, respectively, even under challenging indoor conditions. The proposed method met FCC-required accuracy levels, making it suitable for enhancing the accuracy and availability of wireless 911 calls, aligning with indoor positioning mandates.