Do wireless data signals exhibit spectral autocorrelation?

Signal spectra of wireless data systems are well known to be uncorrelated provided the communicated data sequence itself is white. However, multiplicative processes in wireless transmission systems and multipath fading channels produce spectral correlation. This paper shows that, where spectrum sensing opportunities are short in duration, the sample vector spectrum covariance matrix typically remains purely diagonal. It is also shown that signal spectra may be somewhat correlated in instances where the channel Doppler spread is severe, or where the measurement system has resolution bandwidth smaller than that of the wireless data system.