  With the advancement of communication, the spectrum shortage problem becomes
a serious problem for future generations. The cognitive radio technology is
proposed to address this concern. In cognitive radio networks, the secondary
users can access spectrum that allocated to the primary users without
interference to the operation of primary users. Using cognitive radio network
raises security issues such as jamming attack. A straightforward strategy to
counter the jamming attack is to switch other bands. Finding the best strategy
for switching is complicated when the malicious user is unknown to the primary
users. This paper uses fictitious game for analysis the defense against such an
unknown jammer.
