To solve the problem that traditional spectrum sensing methods require a prior knowledge of the noise power and the primary user signal

and are vulnerable to noise uncertainty

signal set cardinality and contiguity based wideband spectrum sensing schemes are proposed for cognitive radios.The proposed schemes perform wideband spectrum sensing in two phases:estimation of the cardinality of occupied subbands set and decisions of the occupied subband location.Through different cardinality estimations

performance can be effectively improved by exploiting occupied subbands continuity feature.Theoretical analysis and simulation results verify that the proposed algorithm demands no a prior knowledge of the noise power and the primary user signal

and is robust against the noise power uncertainty problem.It can effectively discern subbands status blindly

compared with the conventional spectrum sensing methods.