A two-level defense is required to counter SSDF attacks effectively [9]. At the first level, the data fusion center needs
to authenticate all local spectrum sensing results since there might be malicious users who will eavesdrop the spectrum
sensing results and then launch replay attacks or inject false data. The second level of defense is to implement an effective
data fusion scheme that can determine which sensing information is real. There are several ways to improve existing data
fusion schemes to counter SSDF attacks