Application of Turbo Techniques to GNSS Receivers

‘Turbo’ techniques represent a class of digital processing algorithms that involve iterative and collaborative processing between several receiver components that exchange probabilities or likelihood information. In various fields of data transmission (satellite, wireless, etc.), embodiments of this paradigm, such as turbo error correction, turbo equalisation, turbo synchronisation, turbo interference cancellation and turbo multi-user detection, prove to be very powerful in solving various problems such as noise, multipath, interference, code and carrier acquisition, and synchronisation.

They have brought outstanding performance gains, often approaching theoretical limits. The project team has an excellent background in iterative turbo algorithms and implementation in the communications fields (satellite and wireless). One major challenge of the project is to assess the applicability of these advanced techniques to GNSS receivers.

TGR will perform an algorithm study on how iterative turbo techniques can be applied in the Galileo receiver design in order to improve its performance, in terms of ‘time to first fix’ and the positioning precision in a severe multipath environment.

Description

The TGR project considers the study of advanced signal processing techniques applied to GNSS receivers, particularly those applied to code synchronisation and tracking. A pre-study phase considered several techniques (both existing and original algorithm proposals have been considered) and selected two of them based upon their technical and industrial potentialities. The following two techniques were selected for deep algorithm refinement and performance characterisation:

• the turbo DLL receiver, achieving excellent multipath mitigation;
• the coarse self synchronisation (CSS), an original algorithm aiming at rapid code acquisition.

Intensive algorithm investigations and performance assessment have been carried out by the project partners. Receiver models have been developed and integrated in the Granada environment. A large number of simulations has been carried out to optimise both algorithms parameters.

Objectives

The project aims at devising innovative algorithms inspired from the partners’ knowledge in turbo techniques to address the issues of ‘time to first fix’ and the positioning precision in a severe multipath environment. The implementation aspects are also part of the project – in the form of a detailed hardware architectural study – in order to lead to solutions that can be implemented in today’s receiver hardware technologies.