Implementation of a GNSS-R Payload Based on Software-Defined Radio for the 3CAT-2 Mission

Abstract

The 3 CAT-2 nanosatellite aims at demonstrating global navigation satellite system reflectometry (GNSS-R) techniques for spaceborne applications in the small form of a six-unit CubeSat. There are many challenges involved from a size, processing, and power perspectives. The proposed solution for the payload uses a software-defined radio (SDR) connected to a nadir looking array of dual-band and dual-frequency and dual-polarization antennas to capture the reflected GNSS signals and to a zenith looking patch antenna to capture the direct ones. The SDR is controlled by the payload computer, which retrieves the binary samples and processes the raw data to obtain delay-doppler maps (DDMs) via various techniques. DDMs are then compressed using the fully adaptive prediction error coder algorithm, producing an output more suitable for the limited downlink capabilities of these small platforms.

Sea Target Detection Using Spaceborne GNSS-R Delay-Doppler Maps: Theory and Experimental Proof of Concept Using TDS-1 Data

“…In each scenario, (up to) four eight-satellite constellations of GNSS-R instruments on a 98°-inclined equatorial circular orbit at 500-km attitude have been considered; each GNSS-R satellite is equipped with (up to) 16 parallel tracking channels acquiring signals from the GPS only (Scenario 1), GPS and Galileo (Scenario 2), GPS, Galileo, GLONASS, and BeiDou-2 (Scenario 3). Such constellations provide a global coverage to allow for sea target detection at high latitudes as well and can be implemented based on small satellite platforms, such as 3 Cat-2 [27], [37]. Table II lists the main orbital parameters for the four considered GNSS constellations, while Table III lists the main parameters of the three considered scenarios.…”

“…Earth's surface has been divided in a regular grid in latitude-longitude with a 1°spacing in both latitude and longitude, corresponding to a 120 × 120 km 2 cell at the Equator and a 120 × 40 km 2 cell at 70°N. The specular point position is evaluated from the transmitter and receiver positions by means of the Newton-Raphson method, where the WGS-84 is used to model Earth's surface [27], [37]. The revisit time achieved in the three considered scenarios is shown in Figs. 2-4, respectively, where (a) the average, (b) the median, and (c) the standard deviation of the revisit time computed in the covered areas are shown as a function of the following variables: the number of tracking channels (i.e., different transmitting space vehicles: 1 to 16) mounted on board GNSS-R instruments; the number of GNSS-R satellites (1,8,16,24,32) considered.…”

Software receiver design for GNSS‐R using multiple GNSS satellites as transmitters

“…As one of the critical components in the GNSS‐R technique, the receiver has been attracted a lot of attentions from researchers in this field. Up to now, numerous specialised GNSS‐R receivers have been developed for observation such as the GPS open‐loop differential real‐time receiver [6], the P(Y) and C/A ReflectOmeter [7], and the 3 Cat‐2 payload [8]. Most of the aforementioned receivers were designed to exploit the signal from only one GNSS constellation at a single band, such as the GPS L1 signal [9].…”

3Cat-3/MOTS Nanosatellite Mission for Optical Multispectral and GNSS-R Earth Observation: Concept and Analysis

“…These three concepts converge in 3 Cat-3/MOTS with an innovative combined optical/ Global Navigation Satellite Systems Reflectometry (GNSS-R) [6,7] payload and data fusion solution for high-resolution soil moisture mapping. Since the concept of innovation is linked to a limited time window, the combination of the knowledge provided by the Institut Cartogràfic i Geològic de Catalunya (ICGC) in the field of satellite imagery applied to the management of the Catalan territory, and the experience of the Universitat Politècnica de Catalunya-BarcelonaTech (UPC) in the field of Remote Sensing, in the development of previous small satellite missions ( 3 Cat-1 [8], 3 Cat-2 [9], and 3 Cat-4 and 3 Cat-5 as part of the FYS (Fly Your Satellite) program [10] and FSSCat (Federated Satellite System Catalunya) [11] respectively, both in the design phase), and in the access to facilities to test and qualify space hardware [12] define an optimum environment for 3 Cat-3/MOTS.…”