Direct Sequence Spread Spectrum Signal’s Demodulator Acquisition Implementation Based on Fast Fourier Transform. Part 2. Carrier Frequency Estimation

Signals with direct spread spectrum are widespread in modern communication and navigation systems. Often for communication channels in which such signals are used, significant changes in the carrier frequency in relation to the information speeds of the received signals are characteristic. In particular, for communication channels with significant Doppler shift. Therefore, estimation of the carrier frequency plays a key role in solving the problem of initial synchronization of demodulators of signals with direct spectral broadening. In the first part of the paper, the main approaches to solving the initial synchronization problem were presented. In this part of the paper an algorithm for estimating the carrier frequency based on the analysis of the received signal uncertainty function cross section in the delay plane was proposed. The carrier frequency estimation is based on the fast Fourier transform using an iterative dichotomous search procedure. The results of its efficiency analysis are presented; the variance of the estimates obtained in the implementation of the proposed estimation algorithm are compared with the Cramer-Rao boundary.

direct sequence spread spectrum signals, frequency estimation, Fast Fourier Transform, dichotomous search, Cramer-Rao bound