Radio Frequency Compatibility Criterion for Code Tracking Performance

F. Soualle, T. Burger

Abstract:	In order to ensure the coexistence between the current and future Radio Navigation Satellite Systems within the limited frequency bands allocated to this service, Radio Frequency Criteria (RFC) have to be established. One of the most important of them is the Spectral Separation Coefficient (SSC) which is equal to the inner product of the Power Spectral Densities between the desired and interfering signals. In fact this criterion is appropriate for the impact of interfering signals on the receiver processing steps which use the prompt correlator channel of the receiver, namely the acquisition, the carrier tracking and the data demodulation steps. In [1] another RF-Compatibility criterion, called Code Tracking Spectral Sensitivity Coefficient (CT_SSC) has been introduced. This coefficient could be applied to assess the impact of interfering signals onto the code tracking performance. It is shown that the CT_SSC introduces in the inner product of the PSDs for the desired and interfering signals a sinus squared function which originates from the use of the spacing between the early and late channels during the code tracking phase. When multiplying either the SSC or the CT_SSC with the power of the interfering signal, an equivalent power spectral density, Io is obtained. This white PSD can be directly added to the PSD of the thermal noise, and thus enables to evaluate the receiver performance by the mean of close form expressions in presence of interferences. The purpose of this paper is to apply the CT_SSC in a real RF scenario combining different RNSSs at the same time (like Galileo, GPS, COMPASS, QZSS, SBAS) and to evaluate the variations at a global scale of Io either computed with the SSC or with the CT_SSC. Since, the CT_SSC introduces a new parameter, namely the earlylate spacing (ELS) the equivalent PSD Io should be evaluated for each ELS hypothesis. This would however lead to a huge computational effort. Therefore, it is proposed to present a methodology which enables to predetermine by using the aggregate gain factors, a specific ELS value for which Io is expected to be the largest. Once this specific ELS fixed, the simulations previously described can be performed to evaluate the geographical variations of Io within a reasonable computation time. It will be shown that for some specific pairs of desired and interfering signals, the CT_SSC can vary up to 7 dBs and can be larger than the SSC up to 2 dBs over the range of typical ELS. The ELSs leading to these maxima depend on the position of the main lobes of the desired and interfering signal PSDs. When combining the CT_SSCs for all interfering signals of a specific RF scenario with the appropriate received powers, it will be shown that the aggregate Io obtained with the CT_SSCs has the same order of magnitude as this obtained with the SSCs. This is true for the two proposed RF scenarios (desired signal is either a Galileo E1 OS or a GPS CA signal), but can not be systematically extended to all possible RF scenarios. Therefore it is advised to apply this methodology for each new RF scenario in order to really evaluate the impact of interfering signals onto the code tracking phase. This technical work has been carried out with the support of the Galileo Supervisory Authority (GSA).
Published in:	Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007) September 25 - 28, 2007 Fort Worth Convention Center Fort Worth, TX
Pages:	1201 - 1210
Cite this article:	Soualle, F., Burger, T., "Radio Frequency Compatibility Criterion for Code Tracking Performance," Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007), Fort Worth, TX, September 2007, pp. 1201-1210.
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