| الوصف: |
An increasing number of studies investigate the impact of pulsed interferences in the frequency bands allocated to satellite navigation and show that such interferences can be considered as a significant threat for GNSS receiver performances. Analytical models which include on the one side the pulse parameters (pulse peak power, pulse duty cycle or pulse repetition frequency) and on the other side the receiver front-end parameters (ADC levels, filter bandwidth and pulse blanking threshold) already allow to closely evaluate the corresponding degradations. However, the impact of the spreading codes and especially their interaction with the interfering pulses is usually neglected. It is indeed often assumed that the randomness of the spreading codes enables to ignore any repetitive chip pattern of the code that could correlate with periodical pulse sequences. Moreover, if the code segments corrupted by the high power pulses are blanked too, they are not used afterwards in the correlation process. The balancedness of the remaining codes should not lead to any artifact in the signal-to-noise plus interference ratio (SNIR) estimated with the correlator output. Hence, for pure random codes, the pulse positions should not influence the statistical properties of the correlator output. If however the codes contain series of identical chips, socalled runs, which are synchronized and similar to the pulse sequence and if these runs are not perfectly blanked, the effective SNIR will likely be modified. Although the design of navigation codes should guarantee that such periodical chip patterns do not exist, detailed investigations show that certain properties of non-strictly random codes could still give rise to some unexpected results for the SNIR. It is consequently the intention of this paper to first set-up a more accurate analytical model for the impact of pulsed signals onto the receiver SNIR and secondly to show that in some specific conditions, non-ideal code properties might lead to anomalies of the SNIR degradation in a pulsed interference environment. Such conditions are 1) Non-ideal randomness properties of the spreading sequences, 2) Pulse interference sequences which are synchronized with sub-patterns of the codes and 3) Specific configurations of the receiver front-end which favor such SNIR degradations. |
