Improvement of GPS positioning accuracy when utilizing Klobuchar model with ionospheric conditions in Thailand

Abstract

In global positioning system (GPS) is now widely implemented in the smartphones since the GPS receiver module is integrated in a single chip of CPU. However, over billion of smartphones are based on the single-frequency (L1: 1,575.42 MHz) GPS receiver. Since the positioning error of single-frequency GPS receiver is mainly caused by the atmospheric, especially the ionospheric delay. The Klobuchar model is well-known model which was developed to compensate for ionospheric delay and is currently used for civilian single-frequency GPS receiver. The coefficients of the model are daily broadcast in the GPS satellite navigation message for worldwide users. The remaining errors due to the unique local ionospheric characteristics can cause significant position errors. In this work, we compute the ionospheric delay which obtained Klobuchar model at 3 stations in Thailand: Chiang Mai, KMITL and Surat Thani on 4th September, 2012. The maximum ionospheric delay is 9.9417 meter during day time, while the minimum ionospheric delay is 1.5033 meter during night time. The Klobuchar model can reduce the 95% horizontal errors by more than 34% at Chiang Mai station when we compensate the pseudorange with estimated ionospheric delay.