Doppler Shift Estimation of Signals Modulated by Pseudorandom Sequences
The problem of estimating Doppler shifts and delays of signals modulated by pseudorandom sequences is discussed. It is shown that signals reflected from slow-moving targets hidden among optically opaque wreckages contain some information on targets in the variations of the full phase of a signal over the period that exceeds considerably the pseudorandom oscillation period. For example, these variations in the full phase may result from breathing and heartbeat of those who survived after man-made or natural disasters. Non-correlated and correlated types of noise lead to the errors in a thin structure of code sequences. In this paper a quasi-optimal receiver with non-coherent discriminators is proposed. The receiver has the two parallel channels which are synchronized by phase with a sounding signal. The receiver synthesis procedure, its operating conditions and its characteristics are fully considered. The synthesis is based on the modified non-linear filtering methods. This theory has been used to build the signal processing algorithm. The synthesis procedure consists of two steps. At the first step we assume that signal frequency has no shift and the base structure of the signal processing algorithm has been obtained. At the second step we assume that the structure of the algorithm remains unchanged, and using the theory of signal filtering the filter in the control loop for shifted frequencies is designed. In is shown that the sequences of combined estimates of the frequencies shifts and the signal delay can be used as a model of a dynamic Kalman filter. Fig.: 3. Ref.: 18 pos.
