A Fast Algorithm for GNSS-R Reflected Signals Based on Dynamic Phase Compensation and DBZP

Abstract

Global Navigation Satellite Systems (GNSS) signals provide worldwide coverage and were originally designed to offer passive navigation. However the use of GNSS signals for remote sensing applications has captured the interest of the scientific community in the last decades. Usually, the GNSS-R signals are processed into Delay-Doppler map (DDM), a representation of the power of the correlation of the received signal with a local replica GNSS signal for a range of code delay and Doppler shift values. This is the same procedure used for the direct signal acquisition. Since the power of reflected GNSS signals are very low, a long integration time is needed to obtain better observation quality. As the integration time extended, the code frequency error of the local replica signal and the reflected signal cannot be ignored. In this work we present a method that aims to perform precise DDM generation through signal processing using modified Double Block Zero Padding (DBZP) circular correlation algorithm and code phase drift pre-compensation method. This method effectively suppresses the loss due to code phase miss-matching especially in long time integration and high code frequency circumstance. Analysis shows that the computational burden of the proposed algorithm is 1/9.11 the one of the traditional circular correlation method. Experiments show that the on-board GNSS-R receiver could perform real-time DDM processing for BDS B1I and GPS L1C/A signal. The signal processing accuracy satisfies the requirement of wind field retrieving process. This signal processing system effectively supports the development of China’s first GNSS-R sea surface wind field monitoring satellite system.