GREHDA
GALILEO software Receiver for High Dynamic Applications

Major technical and financial efforts are currently employed in developing ground Galileo receivers, considering mass market, professional market and safety-of-life applications. However, the market constituted by onboard applications can be very satisfactory and profitable for small and medium-size enterprises. The GREHDA project focuses on all those applications that require optimised costs and limited engineering budgets, like size, weight and power consumption. Moreover, apart from space-environment requirements, these applications also have tight high-dynamic technical requirements due to the high relative motion between the receiver and the Galileo satellites.

GREHDA addresses the design of Galileo receivers for space applications with limited financial and engineering budgets. The objectives are: - to design high-dynamic signal processing algorithms; - to propose a conceptual design of the receiver hardware and software; - to define a flight technology validation experiment.

Description

A detailed assessment of Galileo signals as received by high dynamic vehicles, as well as a survey on state-of-the-art spaceborne GPS receiver technologies, have been carried out, together with a dedicated analysis on market requirements and opportunities. Extensions of Galileo signal simulators and analysis tools have been developed, involving modelling of high-dynamic trajectories and generating digitised signals at IF. Basic signal processing algorithms, including acquisition strategies and schemes, as well as steady-state code and carrier tracking structures, have been studied and designed.

To minimise TTFF, the study focused on partial correlation and post-correlation FFT. A warm-start approach using Doppler-aiding techniques has been adopted to reduce the frequency search space. These algorithms were implemented in the NordNav R30 R&D software receiver, equipped with a Galileo extension. Application protocol interfaces dedicated to signal processing tasks allowed a deep customisation of the digital channel behaviour. Tests during validation activities relied on raw IF data streams generated both by the software signal generator, modified to handle high dynamic scenarios, and by the Galileo RF constellation simulator available at the ESTEC Navigation Laboratory.

A preliminary architectural design of a software-defined radio Galileo receiver was carried out based on the FPGA/DSP approach. The key objective was the correct partitioning of the receiver functions between hardware and software domains. Finally, a set of flight technology validation missions has been identified and benchmarked, and a flight experiment has been outlined, to allow testing of the simulated algorithms’ validity and robustness in the real environment.

Objectives

The main objectives of the GREHDA project are:

• to design, develop and validate the software receiver algorithms to fulfil the application-related requirements, starting from dedicated simulation tools and tailoring them to specific needs;
• to propose a conceptual design of the basic receiver hardware and software platforms;
• to define a flight technology validation experiment to test such algorithms in the real environment and specify a detailed configuration of a spaceborne Galileo receiver.