Analysis of Spaceborne GNSS-R Delay-Doppler Tracking

Abstract

For spaceborne Global Navigation Satellite SystemReflectometry (GNSS-R), the delay and Doppler frequency conditions dynamically change, so the compensation of the delay and Doppler errors using tracking is important to the altimetric and scatterometric performances. This work presents the characteristics of the delay and the Doppler frequency in spaceborne GNSS-R, such as the range of them, the Doppler spreading width, and the change rate. They are important considerations for design of the delay and Doppler tracking strategy. The characteristics of delay-Doppler conditions of spaceborne GNSS-R are presented with additional considerations for tracking design. The tracking methods are discussed, and the error impacts are visually demonstrated by using the spaceborne measured data from United Kingdom's Disaster Monitoring Constellation (UK-DMC) satellite.

Crosstalk Statistics and Impact in Interferometric GNSS-R

“…The above equations assume a static scenario and do not take into account the movement of the vehicles during the propagation of the signals. The research done in [16] shows that the errors in For the sake of simplicity, it is assumed that the DDMs are symmetrical in the Doppler axis at f d , although the wind speed direction can produce a skewness [17]. The spread in the Doppler domain is then defined as f d ± γ f d , which results in a width…”

DME/TACAN Impact Analysis on GNSS Reflectometry

“…DME signals from different stations are received with uniformly distributed Doppler frequency in the ± 28 kHz range, while GNSS peaks are uniformly distributed with random Doppler frequency in the ±40 kHz range. The Doppler frequency of the direct and the reflected signals from the same DME station are the same, and they change at a rate smaller than 1 Hz/ms [17]. In these conditions, the Υ(ν) function from (6) has been approximated empirically by:…”

“…Therefore, the sequences of pulses in the direct and reflected signals are different, so they do not cross-correlate at the origin of the DDM, but are uniformly distributed over the delay axis. The Doppler frequency difference between pulses from a same DME station is almost zero as it changes less than 1 Hz/ms [17], so the cross-correlation peaks between same stations are uniformly distributed along the 0 Hz Doppler line. Moreover, the Doppler frequency and delay between different stations is random, so it is the position of these cross-correlation peaks in the DDM plane.…”

“…To do so, AGI STK was used to compute the received Doppler shift in a LEO orbit from several DME stations at different locations. The expected Doppler difference between the received GNSS signals in the up and downlooking antennas will no exceed ±40 kHz [17], so the DDM does not have be computed out of this range. As consequence, the part of the spectrum of two DME signals in adjacent channels that could overlap has a negligible amount of power.…”

The microwave interferometric reflectometer. Part II: Back-end and processor descriptions

“…However, the conventional technique needs a fast delay tracking even in a fix position. The final DDM is obtained as [12] :…”