Improvement of GNSS Positioning with Proper Calibration of Inter-channel and Inter-element Bias in Receiver Front-ends

The performance of GNSS receivers is expected to improve significantly with the availability of L2 signals in the deployed constellations. This improvement in performance will come through better atmospheric (ionospheric) corrections, frequency diversity to resist interference, improved carrier phase ambiguity resolution as well as other benefits. However, the attainable performance improvement is limited by various factors, one of them being the delay differences experienced by the L1 and L2 signals as they travel through the receiver system. These differential delays are called inter-channel (IC) biases. Besides limiting the performance of the GNSS receivers, these IC biases also affect other applications such as atmospheric studies where an IC bias appears as a background ionospheric delay. This paper addresses the problem of IC biases by presenting various methodologies to calibrate such biases. To that end, the total IC bias is first divided into several components and each of those delay biases is calibrated using a different approach. Once calibrated, such biases could be removed from the measurement, leading to an improvement in the position solution. The paper also investigates the extent of variations of such IC biases between different receiver front-ends by calibrating those biases under similar signal conditions simultaneously for several front-ends. The results show that these biases vary significantly between various types of GNSS receiver front-ends, thus indicating that IC biases could be one of the important factors affecting the performance of multi-frequency GNSS receivers.