A software receiver for GPS-IIF L5 signal

Abstract : The block IIF of the GPS will feature a new civil signal, with a bandwidth of 24 MHz. The first launch is scheduled for 2005 and the full operational availability around 2012. This new L5 signal is QPSK-modulated, centered on 1176.45 MHz. Its two components have each a different spreading code at 10.23 Mcps. The in-phase component carries the navigation message, at 100 symbols per second (50 bits per second with a convolutionnal encoder) while the quadrature component, called the pilot channel, carries no message at all. The specified power is such that the received levels on the ground should be -154 dBW (i.e. -157 dBW for each component). In order to closely study the L5 signal, as well as to improve expertise on QPSK radio-navigation signals, CNES (the French Space Agency) has undertaken the development of simulation bench, including a software receiver. This tool comprises a L5 signal generator coupled to a L-band digitizer and a signal processing software, comparable to a software receiver. CNES has chosen this approach not only because it provided a flexible simulation tool for L5 (and any other QPSK radio-navigation signal), but also in order to develop its own capability and expertise in the field of software receiver for radio-navigation signals. The L5 codes and receivers are also studied by ESA, DSTL, UniBW and STNA for instance. This paper presents the work of CNES in the area of software receiver and especially to provide and discuss some interesting results about the L5 signal. First of all, a theoretical analysis of the L5 spreading codes is summarized, showing some little discrepancies in the codes specifications. Since the GPSIIF-L5 signal will share the same band as Galileo E5a, also a QPSK-like signal, the paper presents a methodology to evaluate the interference of one system on another. The objective is to assess the RF compatibility between GPS and Galileo E5a signals. The theoretical analysis is pursued on the software receiver ( using simulated input signals ) to evaluate the acquisition and tracking performances one can expect from the signal. In particular, the use of the pilot channel and its impact on the loop organization (DLL, PLL & FLL) is put in evidence. The complete simulation bench is presented. The main results of these simulations are synthetized and discussed. Their comparisons with the theoretical assessments, both in tracking and acquisition, have allowed not only the tool?s validation but also to verify some signal processing. The acquisition and tracking performances of those receivers are being compared with those of equivalent L1 C/A receiver, especially in the case of low signal to noise density ratio. Finally, an application example of L5 processing, outside the scope of aeronautic, is given. The case of a L5 receiver in GEO/GTO orbit is analyzed. It provides a sensible improvement of the tracking and acquisition capacity.
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Communication dans un congrès
ION GPS 2002, 15th International Technical Meeting of the Satellite Division of The Institute of Navigation, Sep 2002, Portland, United States. pp 1540 - 1553, 2002
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Lionel Ries, Christophe Macabiau, Olivier Nouvel, Quentin Jeandel, Willy Vigneau, et al.. A software receiver for GPS-IIF L5 signal. ION GPS 2002, 15th International Technical Meeting of the Satellite Division of The Institute of Navigation, Sep 2002, Portland, United States. pp 1540 - 1553, 2002. 〈hal-01021711〉

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