GPS L5 and GALILEO E5a/E5b signal-to-noise density ratio degradation due to DME/TACAN signals : simulations and theoretical derivation

Abstract : In the coming years, additional radio navigation signals will be broadcast. For the civil aviation community, the GPS L5 signal and GALILEO E5a and E5b signals are of particular interest. Indeed they will be broadcast in an ARNS band and are expected to increase accuracy, availability, integrity and continuity of service. However E5a/L5 and E5b bands interfering environment is heavy and has been presented in several papers. In particular, Distance Measuring Equipment (DME) and Tactical Air Navigation (TACAN) systems operate in the 960-1215 MHz frequency band also allocated to these new GNSS signals. These pulsed navigation systems consist of an airborne interrogator and a ground-based transponder that emits high-power signals constituting a real threat. The aim of this paper is to propose a new assessment of the impact of such interference on future GNSS receivers. This impact is evaluated through the computation of the equivalent post-correlation signal-to-noise density ratio degradation. Degradation is derived from the Signal-to- Noise plus Interfererence ratio (SNIR) at the prompt correlator output. Obtained results are useful to assess performance of receiver functions using prompt correlator sums such as signal acquisition and carrier phase tracking. DME/TACAN degradations have already been assessed by other authors but we bring here more accurate software and theoretical tools and the corresponding results. Degradation computation is carried out in two different ways. First, a realistic receiver simulator is used that processes useful GNSS signals and interfering DME/TACAN signals. Then, a theoretical derivation of degradation has been developed taking into account separately the effects of low-level and high-level pulses. One important assumption for interference generation is that arrival times of pulses follow a Poisson distribution that is used to assess the effect of pulse collisions. Another important aspect of the theoretical analysis is the consideration of the interference carrier effect yielding low blanker duty cycles but contributing to the degradation. Results obtained with the two methods are compared for a worst case scenario at high altitude (FL 400) with and without safety margins over Europe.
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Frédéric Bastide, Eric Chatre, Christophe Macabiau, Benoit Roturier. GPS L5 and GALILEO E5a/E5b signal-to-noise density ratio degradation due to DME/TACAN signals : simulations and theoretical derivation. ION NTM 2004, National Technical Meeting of The Institute of Navigation, Jan 2004, San Diego, United States. pp 1049-1062. ⟨hal-01022451⟩

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