Patent ID: 6317078
Filing Date: 2001-11-13
Classification: G01S

Abstract:
Method for deducing a pseudodistance to a GPS satellite by reception processing of a GPS satellite signal L2 modulated by an encrypted spreading code Y encrypted by an encryption signal W not available from the GPS satellite, comprising:estimating a Doppler effect affecting the GPS satellite signal L2;transposing the GPS satellite signal L2 into a lower frequency band by utilizing at least one fixed carrier signal produced locally and translated by an expected Doppler shift of the GPS satellite signal L2;demodulating in parallel on three paths the transposed GPS satellite signal L2 with advanced, precise, and delayed versions of a non-encrypted spreading code P produced by an adjustable-phase spreading code local generator, thereby producing respective advanced, precise, and delayed demodulated signals;filtering the respective demodulated signals with a filter matched to a phase and to a frequency of the encryption signal W;re-demodulating the advanced and delayed demodulated signals with the precise demodulated signal so as to delete biphase modulation and to produce two doubly demodulated signals;calculating respective powers of the two doubly demodulated signals;locking a phase of the adjustable-phase spreading code local generator when the two doubly demodulated signals are of equal powers; anddeducing a pseudodistance to the GPS satellite from a difference in said phase of the adjustable-phase spreading code local generator when said generator is locked and a phase of the GPS reception signal L1.