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The Earth's upper atmosphere presents a region particularly rich of free electrons, the ionosphere. Such high concentration makes the ionosphere the major natural contributor to the degraded quality of the GNSS signals received at ground. In polar regions, such as in Antarctica, this degradation can be stronger, creating serious problems in using GNSS devices for logistic and scientific purposes. An ionosphere monitoring station, based on a GNSS signal acquisition system and on a software radio receiver, has been installed in two research stations in Antarctica, in the frame of the DemoGRAPE project. The full system is not only able to monitor TEC and scintillation activity in GPS L1 C/A and L2C signals, but also to grab and store raw unprocessed samples for post-processing analysis by means of software radio techniques. This paper presents the description of the setup and of the installation of the system as well as a report of the first results obtained by processing the data acquired during the first week of operation.

In the recent years, the use of GNSS receivers for on-board satellite orbit determination has become a common solution, as it considerably simplifies the overall architecture if compared to traditional orbit determination system such as radiometric tracking. Different challenges have to be faced while designing a GNSS system for this type of application, since in general the terrestrial receiver are not designed to guarantee their performances if placed in and orbital environment. The differences can be grouped in two main areas: the first is related to the signal properties, as higher signal strength variations, higher Doppler and Doppler rate must be accounted for, to design the proper acquisition and tracking strategy. The second group of differences is related to the space environment that affects the electronic systems in general trough severe temperature variation and the various types of radiations. These aspects are combined together in the design of a novel FPGA based GPS and Galileo receiver for space applications. This paper describes first the receiver requirements, that were defined trough simulations, using a GNSS full system and navigation software simulator, which provides also PVT accuracy estimation by the implementation of the navigation filter. The receiver hardware is based on the Xilinx FPGA, which incorporates a PowerPC in form of hard processor. The paper describes also the electronic hardware, together with the tracking algorithms, providing details about the combined third order PLL carrier aided DLL implementation. On-board navigation algorithms are also discussed with respect to the relevant error sources, showing that the achievable positioning accuracy provided by the simulator ranges from sub-meter for the dual frequency solution to one-three meters for the single frequency solution.

International audience; This paper studies the impact of clock sampling jitter on signal tracking in a dual band L5/E5 and L1/E1 Direct Sampling GNSS receiver designed for Civil Aviation. A model of the sampling clock jitter due to thermal noise is established and related simulation results about the phase tracking error standard deviation at the output of the PLL are presented.

International audience; This paper studies the application of the Direct Sampling technique to GNSS receivers dedicated to Civil Aviation usage. After describing the specific spectral environment to be withstood by such receivers, an analysis of the digitization process is conducted, leading to design guidelines.