Cognitive Radio is a revolutionary technology that made significant progress in the effective use of the frequency spectrum. The technology itself can be dynamically adjusted so that the proper utilization of the available Radio spectrum can be made. According to various studies conducted, it is observed that the bulk of each frequency band allocated to users leaving unused. The Cognitive Radio can use these parts of the spectrum that called spectrum holes.Inherent nature of this technology creates the chance for the attacker in these networks. This vulnerability that created due to the inherent nature of Cognitive Radio technology, Can severely impact on the safety and quality of service in these networks. In this paper, we focus on the primary user emulation attack. In this attack, an adversary transmits signals whose characteristics emulate those of incumbent signals. We proposed the method for reducing the effects of primary user emulation attacks in Cognitive Radio networks. This method suggests the technique that can merge with spectrum sensing method and can resistant these networks against the primary user emulation attacks. Finally, with run some simulation, we examined the performance of this proposed method in detection of primary user emulation attacks in these networks.

Either natural or man-made a disaster is defined as unexpected destructive event that causes damages and malfunction of existing systems and services all around the disaster area, these destructive effects are unfortunately beyond the capability of local authorities to recover and respond immediately, the disaster recovery plans are immediately initiated so that rescue and aid operations can help those who are trapped in disaster area to survive, those efforts need to be controlled and coordinated with reliable communication systems that are more likely partially or fully disabled due to the disaster, the capabilities of Cognitive Radio technology enables it to play a significant role in providing efficient communication services for the rescue teams and headquarters as well as trapped victims, in this paper, we survey the Cognitive Radio architectures that can replace the Software Defined Radio SDR in order to reduce the network expenses in terms of network size and network computational complexity.

The lack of frequency, low utilization and static allocation of spectrum have been important problems in wireless network in prior methods. To solve this problem, a concept called Cognitive Radio Network was introduced to allow the use of empty spaces of licensed spectrum. The purpose of this paper was to provide an intelligent method for detecting and allocating spectrum in Cognitive Radio network. In this method, Hidden Marcov model is used to predict the status of free or occupied channels, then some types of learning automata are used to allocate channel to secondary users. Also, it is a way to reduce the waiting time of users who were simultaneously requesting a channel to use a mechanism for fairness in this algorithm. The simulation results indicated that the proposed method is more effective in channel allocation to secondary users thanks to using the proposed mechanisms whose results have a greater convergence speed.

In this paper, a new joint admission and power control scheme is introduced for wireless Cognitive Radio networks. It is assumed that the Cognitive Users (CUs) arrive sequentially in time and exploit the spectrum simultaneous to the licensed primary users. The objective is to minimize the blocking probability of the new arriving CUs while the interference limit constraint of primary users is not violated and the quality of service (QoS) requirements of the current admitted CUs is satisfied.To these aims, an algorithm is developed for CUs admission in which the power of the new arriving CU gradually increases according to two predefined parameters, Primary Interference Margin (PIM) and Secondary Interference Margin (SIM). In addition to protect the QoS of the current CUs, their powers are boosted by a particular parameter, which is calculated based on PIM and their maximum allowable power. Moreover, the PIM guarantees the protection of the primary users during the admission phase of the new arriving CU. Two admission control algorithms have been proposed, a safe admission which tightly admits a new CU and a moderate one which loosely accepts a new CU. Simulation results are provided to evaluate the performance of the proposed algorithms in terms of the blocking and outage probability and compared with recent proposed schemes.These results show that the proposed algorithms outperform the similar schemes while they are more suitable for a practical scenario.