Résumé : 

GPS receiver for space applications is a valuable sensor in space applications, able to fulfill various missions. Unlike the receiver for terrestrial use, stringent export rules make it challenging, sometimes impossible, to access this kind of device. Satellites are also vital in these days. Cost is a significant constraint for space projects in developing countries, as well as access to sensitive technologies. CubeSats is a standard created to build nanosatellites with rapid development and lower production costs, using COTS components, but it is not suitable for professional applications. CONASAT is a Brazilian project of a constellation of CubeSats for a critical system to collect meteorological data in Brazil. Requirements of this project define the use of COTS components in the project, the construction of a GPS receiver, and the development of new technologies for the Brazilian Space Program. Further, the limited dimensions of this kind of satellite add other levels of restrictions on size, mass and power consumption. This study aims to propose alternatives in terms of hardware architectures, acquisition algorithms and the use of COTS for space applications, taking as guidelines the requirements of CONASAT.

A review of literature of existing GPS receivers for space and the algorithms used in the GPS receivers for space show that the acquisition of GPS signals in time domain remains as the state of the art for GPS receivers applied in nanosatellites. A classification of GNSS receivers is proposed in this thesis. Also, the study proposes several strategies for the acquisition of GOS signals in time domain in a new algorithm, decreasing its complexity, and saving energy consumption as a consequence. The algorithm was tested using signals with low and high Doppler, as in space, in worst conditions. Results showed the proposed algorithm outperforms the state of the art algorithm in all compared aspects, with low requirements in hardware resources. Savings in the number of calculations regarding the state of the art algorithm can reach from 50% to 95%. The thesis also proposes a flexible hardware architecture fitted to the new algorithm, as well as for GPS receiver intended for CONASAT. The results obtained his study gives a general view of the design problem for a GPS receiver for nanosatellites and address problems on the complexity of acquisition algorithms for nanosatellites. Results obtained for the algorithm and the proposed architectures allow the designer envisages new hardware architectures for new GPS receivers for space applications.