GNSS C/N0 Degradation Model in Presence of Continuous Wave and Pulsed Interference

Abstract

In the context of GNSS L5/E5a interference environment dominated by DME/TACAN and JTIDS/MIDS pulses, RTCA DO-292 [1] proposes to implement a temporal blanker mechanism to mitigate the detrimental impact of the pulsed interference signals on the nominal functioning of a generic GNSS receiver. Moreover, RTCA DO-292 [1] also proposes a model to compute the received useful signal C/N_0 degradation due to the interference signals by increasing the noise power spectrum density (PSD) N_0, called the effective N_0, N_0_eff, where the N_0 increase is expressed as a function of the blanker duty cycle, bdc, and the equivalent noise level contribution of the nonblanked interference, E_I . However, the proposed computation of these two terms in RTCA DO-292 [1] makes some assumptions or neglect some effects which may decrease the final accuracy of the computation. On one hand, the collisions between pulses are not completely modelled. On the other hand, the effect of the time-domain blanker mechanism over the pulsed interference signal PSD is over bounded in RTCA DO-292 [1] by assuming a completely spread PSD over the Radio-Frequency Front-end (RFFE) filter bandwidth. In this paper, the pulse collisions effects are commented, and the true post-blanker pulsed interference signal PSD is introduced through the application of the spectral separation coefficient (SSC) with the local replica PRN code signal PSD to propose a new more accurate formula for the equivalent noise level contribution of the non-blanked interference. Moreover, the C/N_0 degradation formula is derived, and its limitations are pointed out. Finally, the new proposed formula is validated through simulations for a simplified DME/TACAN signal and for DME/TACAN signals in the US hot spot.