A New Approach for Accurate Time Synchronization Using Chirp Signals

In analog receivers, the use of matched filtering with linear frequency modulated signals constitutes an effective means for detecting the presence of an incoming frame as well as for estimating the symbol timing offset (STO). However, in digital receivers, the discrete nature of the corresponding polyphase codes leads, under certain conditions of carrier frequency offsets, to a significant degradation at the output of the matched filter, which, consequently, can result in erroneous STO estimations. Exploiting the symmetry of a reference sequence consisting of a polyphase code and its complex conjugate, this work proposes a new algorithm based on reversed autocorrelation (RC) to improve the accuracy of the STO estimation obtained by matched filtering. On the one hand, the theoretical analysis demonstrates the superiority of matched filtering over RC in terms of detection performance in the low signal-to-noise ratio regime. On the other hand, it is shown by means of numerical evaluation that the RC can efficiently resolve the STO estimation ambiguity.