Quality Monitoring for Multipath Affected Signals Using an Extended Kalman Filter

The ability to monitor and detect any disturbances on the PRN code signals transmitted from the navigation satellite constellation is of primary importance. It is known that the tracking performance of a navigation receiver stems from the correlation property of the PRN code signals transmitted. These anomalies can be detected in several different ways, either observing the outputs of navigation user receivers, or processing the received signal within the receiver. Quality control is the process that defines how well the solution of a problem is known and in the context of navigation, it consists of assuring an agreed level of accuracy, reliability and robustness for the measurements. In this work a modified version of the conventional tracking scheme will be proposed with the aim of monitoring the quality of the measurements at the signal processing level. The proposed tracking scheme is able to give a measure of the distortion of the correlation function and consequently, of the reliability of the signal tracked. In particular the problem of multipath distortion is considered The amplitude and multipath delay can be estimated with an extension of the linear Kalman Filter which can be implemented inside the traditional DLL architecture. Simulations show that due to its prediction capability, Kalman Filter enhances the robustness of the system when weak signals are present or there is loss of lock on the signals, trading off the performance improvement with an increase in complexity of the new architecture. The recognition of a multipath corrupted signal estimating the amplitude and delay of the reflection can be used to select the more reliable pseudo-range measurements for the evaluation of the positioning equations. Mitigation of the multipath effects may be performed where the number of tracked signals is not sufficient.