Carrier phase difference estimation method based on DDMR-assistance for GNSS-R altimetry

A carrier phase difference estimation method based on the delay-Doppler map receiver (DDMR)-assistance for (GNSS-R) coastal altimetry was proposed. The system structure and the signal processing method were given. The proposed method, which can avoid the complicated search for the GNSS spreading codes, uses the code phase difference observed from DDMR as the estimated time-delay between the spreading codes of the direct signal and the reflected signal, and then delays the tracked codes of the direct signal to achieve the open-loop tracking of the reflected signal. Field experiments with real coastal receivers demonstrate the effectiveness of this method, which can steadily track the weak reflected signal and accurately extract the difference of the carrier phase. The experiment results show that the altimetry accuracy is about 2.5 cm without data average or 0.6 cm with 0.5 s average.