Performance of multicorrelators GNSS interference detection algorithms for Civil Aviation

Abstract : For GNSS civil aviation applications, it is necessary to be able to guarantee the required level of performance specified by ICAO during a given phase of flight. The use of several GNSS components such as various signals, constellations or augmentation systems, sometimes redundant, helps monitoring the system robustness against several sources of perturbations like ionosphere or jammers for instance. In case of perturbation preventing one of the needed components to meet the phase of flight required performance, it is necessary to be able to switch to another available component in order to try to maintain if possible the level of performance in terms of continuity, integrity, availability and accuracy. But, to this end, future combined receivers must be capable of detecting the largest number of degradations that should lead to the loss of one GNSS component. Among the perturbations, one can note atmospheric disturbances, multipath, cycle slips, interferences. It is consequently necessary to identify and test degradation detection means that will enable if possible the receiver to maintain the level of performance requirement during an aircraft flight. Because of the interests in civil aviation and the restrictive requirements associated, it is interesting to focus on the degradation detection during LPV phases of flight. The interference is among the most feared events in civil aviation use of GNSS. Detection, estimation and removal remain an open issue and may affect pseudoranges measurements accuracy as well as integrity, continuity and even availability of those measurements. In literature, many different interference detection algorithms have been proposed at the front-end level of the receiver. For instance making chi-square tests at the ADC level, as in nominal conditions, the ADC bins distribution is Gaussian. Other non exhaustive means are to study the design of the receiver antenna or to make a spectral selectivity using filters. However, detection within tracking loops is not widely studied to our knowledge that is why it is an interesting investigation way that may complete other detection means, as proposed in [Bastide, 2001]. The goal of this paper is to estimate the performance of detection algorithm of Carrier Waves and Narrow Bands interferences. The main results are missed detection probability and the non-detected tracking error induced by interferences. Indeed, those types of interferences may affect powerful GPS L1 C/A or Galileo E1 code spectrum lines and may produce Misleading Information. It is consequently important to study the effects of such interferences on different spectrum lines and with different settings, varying the amplitude and for Narrow Bands, the bandwidth of this perturbation. The detection algorithms used are based on multi correlator receiver outputs to detect the I and Q correlation distortions due to interferences. The paper starts with the presentation of the detection technique. Performance analysis is then conducted taking into account required continuity during LPV phase of flight, to determine a threshold on the interference detection criteria (FFT of the correlator outputs). Interference missed detection probability is then estimated and finally the algorithm integrity performances are discussed. To comply with actual conditions, as the receiver is supposed onboard a flying aircraft, tests were conducted under multipath conditions modelled with the DLR Aeronautical Channel, taking into account the ground reflection and fuselage echoes during LPV. In addition, simulations were performed under all kinds of dynamics, complying with DO 229 d specifications and interim Galileo MOPS. The results indicate these techniques are good detection means under actual conditions, and do not require a too large number of calculations. The inclusion of the proposed algorithms before Receiver Autonomous Integrity Monitoring algorithms and combined integrity results are discussed. Further studies should provide results on the accuracy of interference estimation and repair algorithms.
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Communication dans un congrès
ION NTM 2008, National Technical Meeting of The Institute of Navigation, Jan 2008, San Diego, United States. pp 142-153, 2008
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Christophe Ouzeau, Christophe Macabiau, Benoit Roturier, Mikaël Mabilleau. Performance of multicorrelators GNSS interference detection algorithms for Civil Aviation. ION NTM 2008, National Technical Meeting of The Institute of Navigation, Jan 2008, San Diego, United States. pp 142-153, 2008. 〈hal-01022138〉

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