Blind estimation for PN code of LFM-PRBC signal based on DPT and spectrum shifting

A new approach is proposed to blindly estimate the pseudo noise (PN) code of compound signal combined linear frequency modulation (LFM) and pseudo-random binary phase code (PRBC), which is based on methods of discrete polynomial-phase transform (DPT) and spectrum shifting. Firstly, the square method is adopted to eliminate phase mutation. Then, apply DPT method to estimate the chirp rate, which is used to reconstruct second order exponent. The original compound signal is multiplied by the conjugated second order exponent to get a new compound signal. And then, the original PN code can be restored from the real part of the new compound signal by the way of spectrum shifting. Simulation results show that the approach can correctly estimate PN code when the signal-to-noise ratio (SNR) is 3 dB, and performance will be improved with the increase of sub-pulse number. It also has a better performance compared with the method of FM-AM time-frequency analysis.