A baseband MLE for snapshot GNSS receiver using super-long-coherent correlation in a fractional fourier domain

Abstract

Low-cost global navigation satellite system and global positioning system(GPS) receivers require reliable baseband processing to guarantee accurate position-ing. However, classic baseband performance is limited in challenging cases due to the characteristics of traditional loop filters. Accordingly, a snapshot base -band maximum likelihood estimator (MLE) using super-long coherent integra-tion (S-LCI) in a fractional Fourier domain (FrFD) is proposed to upgrade the traditional frequency/phase/delay lock loop tracking algorithms. First, applying the S-LCI correlation in an FrFD increases the accuracy of a weak and dynamic signal estimation. Tolerance of the initial guess error in the snapshot baseband processing is then relaxed by the MLE. Finally, a gradient descent algorithm accelerates the convergence of signal estimation. Moreover, we derive the Cramer-Rao lower bound for the proposed MLE. Both numerical simulations and real-world experiments based on this GPS receiver prototype verify the effectiveness of its high-accuracy estimations of weak signals, strong tolerance for large initial guess errors, and prompt responses to converging.