The cooperative communication system has gained lots of interest due to effective utilization of the allotted spectrum. Spectrum sensing techniques are a key factor for the cooperative communication system. A number of sensors are deployed to sense the spectrum hole. The group or clusters of the sensor are used to make out the decision about the spectrum hole. The presence of malicious sensor affects the performance of spectrum sensing. In this paper, the trust on the group or cluster has been identified based on the fuzzy classification. The fuzzy classifier takes the input in terms of reporting cluster trust value, neighborhood trust value and primary weight index. The membership values of these three linguistic variables are used by fuzzy interference system to decide the trust value of the group or cluster. The number of malicious user has been introduced during the simulation and performance has been identified. The Eigenvalue-based spectrum sensing is also simulated in this paper and the effect of different SNRs on the decision accuracy is shown.

The Cognitive Radio (CR) is expected to be the next Big Bang for the wireless data communication system. Research on dynamic spectrum access has started in many countries. Many organizations have also been motivated to start work for standardization of this technology for various applications. To finalize the state-of-the-art in the regulatory and standardization activities on CR all over the world, there is a need to understand and explore the CR concepts and the influence of this technique on the future of wireless communications. CR concepts can be applied to a variety of wireless communication scenarios. The major functions and applications of CR, components of CR and implementation issues need to be reviewed.

As the wireless devices and their applications are increasing day-by-day, the available radio spectrum is not sufficient to give spectrum access to all the users. CR is a technology that deals with this spectrum shortage problem. Dynamic Spectrum Access (DSA) has been proposed to utilize radio spectrum more efficiently as compared to the conventional spectrum access technique. It is a spectrum sharing technique. Spectrum can be licensed to more than one user using DSA technique. Communication system has two types of users. Licensed users are one of them. In CR, licensed users are called primary users. They have permission to access the spectrum. However, for primary users also that spectrum is not exclusively allotted. There is another category of users referred to as secondary users. They are also called unlicensed users. CR allows secondary users to opportunistically utilize the unused spectrum bands or white spaces or spectrum holes. They can occupy the channel and transmit data if no primary user is present. If a primary user is present, the secondary user does not get access. For this, CR needs to sense the white spectrum holes of available spectrum. Sensing the spectrum means to find whether the spectrum is used by primary user or not. These white spectrum holes are completely vacant and can be used by secondary users for transmission without causing interference to the primary users. Thus, secondary users can reuse the channel in an opportunistic way and thus efficiency of spectrum utilization is increased.

Telecommunications Journal, Cognitive Radio (CR), Primary user, Secondary user, Malicious user, Trust value, Fuzzy classifier, Spectrum sensing, Probability of detection.