Bias suppression of GPS measurement in inertial navigation system vertical channel

GPS measurement may include bias type noise in it. In this case, the measurement bias aggravates the estimation ability of a filter for inertial navigation system and corrupts the estimate of the filter. If the magnitude of the bias is large, fault detection and isolation techniques are often used for rejection or suppression of the effect of the bias. However, if the magnitude of the bias is small, the fault detection and isolation techniques cannot reject or suppress the effect of the bias. In this paper, the INS vertical channel using a barometer and GPS is considered. The GPS measurement is supposed to have bias noise. The magnitude of the bias is supposed to be small, therefore the FDI techniques cannot reject or suppress. For this case, a method of estimating and compensating the measurement bias in GPS output is proposed. In this scheme, the residuals of GPS output with measurement bias are stored for appropriate duration and, with these residuals, linear equations of measurement bias is developed. Then, simple least square method can estimate the bias, and, with this estimated value, GPS output can be compensated and a portion of the bias can be removed. In simulation results, it is shown that the scheme has an effect of measurement bias suppression.