Conjugate transfer function compensation of ionospheric refractive effects

摘要

The next generation of GNSS signals will bring alongside them a new generation of errors. Understanding these errors and their sources can help their correction efforts to improve their PNT solution accuracy and to better support remote sensing applications. Some newer signals such as GPS L1C and L5, Galileo E5, BDS-3 have wider spectral coverages. The wide spectral coverage will subject the signals to more dispersion due to ionospheric effects, such as refractive code delay determined by the total electron content (TEC), leading to consequences such as correlation peak loss, widening, and offset which directly impact ranging accuracy. This study investigates the use of TEC estimations to compensate not only the delay error, but also the dispersion on wide bandwidth or spectral signals. By applying a frequency-dependent transfer function to the received spectra before the correlation process, the dispersion can be compensated and hence the effects on the correlation peak distortion are reduced. This transfer function is essentially the conjugate exponential of the dual-frequency TEC estimate phase delay. Simulated L1C signals are generated and reprocessed through the ionosphere by this transfer function to test its use. The TEC is varied to show how the correlation peak, width, and offset are affected. Then the described transfer function conjugate is applied to the ionospheric affected signal models and re-correlated with the replica to quantify how the correlation has improved in comparison to the pseudorange measurement ionospheric delay model. This comparison is the measure of how necessary applying this type of correction will be. Results show that for the L1C bandwidth, the pseudorange measurement ionospheric delay model is comparable to the conjugate transfer function.