  In cognitive radio it is of prime importance that the presence of Primary
Users (PU) is detected correctly at each of the time. In order to do so the
help from all present Secondary Users (SU) is taken and such a taken is known
as co-operative spectrum sensing. Ideally it is assumed that all the secondary
users give the correct result to the control center. But there are certain
conditions under which the secondary users deliberately forward wrong result to
the control center so as to degrade the performance of the cognitive network.
In this paper we study the different techniques for detecting the malicious
users or outliers. We take into consideration practical environmental condition
such that the received signal of the secondary users is made to undergo fading
and noise is also introduced in the signal. We further go on to examine each of
the outlier detector techniques and find out the most suitable at various
instants.
