An Efficient Time-frequency Algorithm for the Weak Signal Acquisition of Modernized GNSS Signals
The new GPS/Galileo/Compass signals use much longer code lengths and higher code frequencies than the GPS L1 C/A signal. As a result, they can provide improved ranging and anti-jamming performances. Unfortunately, their acquisition complexity is significantly higher, especially in the high sensitivity or weak signal acquisition context. Acquisition of very weak signals requires long integration times, but the integration time is often limited because of the code phase shifting induced in the receiver by an unmatched code frequency. Therefore, for the purpose of minimizing the acquisition time, a new algorithm that we named “slope parallel frequency and code searching (SPFCS)”, has been developed and is presented in this paper. This algorithm combines the parallel frequency searching and parallel code phase searching together in a novel way, and satisfies the requirements for providing standalone high sensitivity (i.e., without any network or additional sensors’ assistance). In order to assess its performance, we consider in this paper the acquisition of the GPS L5 pilot signal. Our simulation results indicate that the proposed algorithm can successfully acquire, without assistance, L5 signals as low as 15 dB-Hz with 35 kHz Doppler shifts, and a computational burden over 2 to 4 times smaller at 15 dB-Hz and 18 dB-Hz, respectively, as compared to the traditional parallel code phase search (PCS) or double block zero padding (DBZP) methods.