The Namuru receiver as development platform for spaceborne GNSS applications

Abstract

GPS is a well established navigation system in current spaceflight missions. Affordable GPS receivers for small satellite and sounding rocket missions are usually based on Commercial Off The Shelf (COTS) products. Many of these receivers are limited to single frequency tracking and utilise custom ASICs for the signal processing. The Phoenix receiver is an example of a commercially available receiver with custom software modifications by DLR. This receiver is based on the GP2021 baseband processor and is therefore not flexible enough to implement anything else besides GPS L1 tracking. To overcome this limitation it has been decided to migrate to the Namuru GNSS receiver platform for the development of new GNSS applications. The Namuru system is based on a reconfigurable FPGA and has been developed by the University of New South Wales (UNSW). This platform allows the baseband processing hardware to be completely customised and allows the implementation of software for different areas of research. The DLR’s research projects aim at multiple frontend systems, new signals and spaceborne GNSS reflectometry. As a first step we have ported the flight proven Phoenix software to the Namuru receiver. The accuracy of the navigation solution has been validated in both low earth orbit and ballistic rocket simulations and a comparison with the Phoenix receiver is shown. In the second step, an antenna array system for spaceborne GNSS reflectometry is being implemented. Narrowband Beamforming is performed after carrier demodulation or PRN correlation, significantly lowering the requirements for the analogue front-end and at the same time allowing the use of already space proven hardware and software GPS architecture available at our department. The paper provides a description of the Namuru development board and preliminary results obtained in a signal simulation test bed. In addition, ongoing developments for special applications such as GNSS reflectometry are addressed.