Spectrum Sensing in Cognitive Radio

Abstract

In modern wireless communications the spectrum is allocated to fixed licensed users and on the other side the number of wireless devices are increasing rapidly, that has lead to spectrum crunch. As the spectrum is precious it has to be utilized efficiently. The solution to mitigate this problem is “Spectrum Sharing”. One of the innovative approach to recognize and access the spectrum holes present in the licensed spectrum is ‘Cognitive Radio (CR)’. Spectrum sensing is a base for the performance of all functions performed by the Cognitive Radio (CR). Cognitive radio recognizes the unused spectrum and shares it to secondary users (SU’s) without creating harmful interference to primary users (E.g. Cellular Networks, TV). Literature discusses various SS techniques like ED, CSD, CMME with their advantages and disadvantages. ED is most preferred in CR because of simple implementation and semi-blind nature. But its performance is very poor at low SNR bound. So other combined techniques are preferred over the ED to enhance sensitivity of CR. So, thesis proposes Two Stage Spectrum Sensing as preferred in IEEE 802.22 standard. Combination of both ED and CMME method to enhance accuracy and timing of sensing in coarse and fine sensing stage respectively, is proposed and compared with individual sensing techniques. As the type of sensing takes place in two-level, the weak primary signals present in the spectrum are easily detected. If the signal is not identified in the first stage, it will be sensed in the second stage even if it is not detected, it can be declared as the absence of PU in the spectrum. In this thesis, the performance of Single user and Global decision using Modified Deflection Coefficient (MDC) method is observed. Extensive study of cooperative SS and optimal cooperative sensing is done and results are presented