Development of a Multi-Frequency Adaptive Kalman Filter Based Tracking Loop for an Ionospheric Scintillation Monitoring Receiver

Abstract

Rapid and random temporal fluctuations in amplitude and phase of GNSS signals caused when they are propa-gating through localized irregularities in electron density of the ionosphere are called amplitude and phase scintil-lation, respectively. Scintillation affects signal acquisition, operation of PLLs (Phase Lock Loops) while tracking, and can lead to carrier cycle slips, navigation data bit errors and/or complete loss of lock. The loss of tracking may affect the availability and accuracy of receiver posi-tions for short period of time, when less than four satel-lites are available for position computation. The use of carrier phase measurements with cycle slips and disconti-nuities, under strong scintillation, is a challenge for scintil-lation monitoring applications. Monitoring the ionosphere using GNSS signals is an important application in space-weather monitoring to understand scintillation effects on receiver operation and its performance. This paper analyzes the Kalman Filter (KF) based track-ing performance of combined GPS L1, L2C and L5 signal tracking by taking advantage of the dispersive nature of the ionosphere. It also incorporates an adaptive algorithm for combined L1-L2C-L5 KF tracking in which the KF self-tunes the covariance matrix based on scintillation indices. To evaluate performance of the combined KF based tracking algorithm, its probability of loss of lock and tracking jitter are compared with that of single frequency KF based tracking algorithm for both adaptive and non-adaptive cases.