Abstract: Cognitive Radio (CR) is a self-adaptive wireless technology that can detect available channels automatically in a wireless spectrum and configured dynamically. Spectrum sensing in CR is the fundamental activity to detect unused spectrum holes in an opportunistic manner. In Spectrum sensing, various methods have been proposed and studied exhaustively by the CR researchers. Blind spectrum sensing methods such as an Eigenvalue based Detection (EVD) and Energy Detection (ED) does not require any information of the transmitted signal characteristics, the channel or the noise-power, which are unknown at the receiver. The main aim of this work is to sense the spectrum at very low Signal to Noise Ratio (SNR) under frequently changing wireless environment. A combined blind spectrum sensing is proposed based on an adaptive SNR threshold calculation which achieves better sensing accuracy than the two individual detectors. In this paper spectrum sensing is done for DVB-T signals in the VHF band which has been declared as an operating band for Cognitive users.

Keywords: Cognitive Radio, Eigenvalue based detection, Energy detector, low SNR, Spectrum sensing.