In this section, the spectral analysis of the Doppler stretched signal received in the case of constant relative radial speed between TX and RX is addressed. The second-order statistical characterization is made in both time and frequency domains and both continuous-and discrete-time cases are considered. Sampling theorems are proved to obtain input/output relationships for discrete-time sampled signals which are formally analogous to their continuous-time counterparts. Proofs are reported in Section 7.10.
Let us consider the continuous-time Doppler-stretched signal (Section 7.3):
It is a time-scaled, delayed, and frequency-shifted version of the transmitted signal xa(t). Its Fourier transform is given by (Section 7.10)
Let xa(t) exhibit (conjugate) cyclostationarity. Then, also ya(t) exhibits (conjugate) cyclostationarity and its cyclic statistics are linked to those of xa(t) as follows.
The cyclic autocorrelation function and the cyclic spectrum of ya(t) are given by (Section 7.10)
Thus, if xa(t) exhibits cyclostationarity at cycle frequency ...