Figure 1
From: Higher-Order Cyclostationarity Detection for Spectrum Sensing
Baseband signal frequency spectrum (top) and SCD at the symbol rate (bottom). The frequency spectrum results from the repetitive discrete signal spectrum and the filter shaping. The SCD is measured by the correlation between two frequency bins centered on 
and 
where 
is the symbol rate. The symbol rate feature exists for baseband PAM/QAM signals if there is some excess bandwidth in the system.