Performance Analysis of Secondary Users in Heterogeneous Cognitive Radio Network

Continuous increase in wireless subscriptions and static allocation of wireless frequency bands to the primary users (PUs) are fueling the radio frequency (RF) shortage problem. Cognitive radio network (CRN) is regarded as a solution to this problem as it utilizes the scarce RF in an opportunisticmanner to increase the spectrumefficiency. InCRN, secondary users (SUs) are allowed to access idle frequency bands opportunistically without causing harmful interference to the PUs. In CRN, the SUs determine the presence of PUs through spectrum sensing and access idle bands by means of dynamic spectrum access. Spectrum sensing techniques available in the literature do not consider mobility. One of the main objectives of this thesis is to include mobility of SUs in spectrum sensing. Furthermore, due to the physical characteristics of CRN where licensed RF bands can be dynamically accessed by various unknown wireless devices, security is a growing concern. This thesis also addresses the physical layer security issues in CRN. Performance of spectrum sensing is evaluated based on probability of misdetection and false alarm, and expected overlapping time, and performance of SUs in the presence of attackers is evaluated based on secrecy rates

A Game Theoretic Analysis of the Security of Secondary Users in the Presence of Active Attackers in a Cognitive Radio Network

Wireless communication is one of the most booming industries right now. With its expansion all over the world, number of wireless device users is increasing in a seamless way. Due to recent increase in the number of devices in wireless communication network, frequency is becoming more and more scarce day by day. Fortunately Cognitive Radio has emerged as a solution to this crucial problem of spectrum congestion. In the beginning of its initialization resource allocation, spectrum sensing and management were the major focuses of researchers. Security issues are gaining more and more attention with the steep advancement of cognitive radio. Now-a-days security is one of the major issues that garners the heed of the researchers of cognitive radio. Two of the most vital characteristics of cognitive radio, spectrum sensing and sharing it with other secondary users, make it more prone to security attacks. Security issues in cognitive radio network are addressed in many recent papers, but most of them consider the impact of eavesdroppers or jammers separately on the security issues of secondary users. To our best knowledge this is the first study which considers the impact of both eavesdroppers and jammers combinedly on the performance of secondary users in cognitive radio network. We assume the presence of both eavesdroppers and jammers in a single cognitive radio network as active attackers. In this paper we have developed a system model which accommodates sets of secondary users, eavesdroppers and jammers. Based on this system model, utility functions are generated. Number of devices (secondary users, eavesdroppers, and jammers), variation in transmission power, transmission cost per unit power of these devices (secondary users, and jammers) and their relative distances have dire impacts on the utility of these devices. Finally we implement game theory with the help of the utility functions and reach an equilibrium point

Performance Analysis of Spectrum Sensing in Cognitive Vehicular Network for Mobile Secondary Users

Due to the rapid growth in wireless devices, fixed spectrum allocation policy is soon going to be non-existent and smart spectrum allocation policy is going to be the best choice for perfect utilization of such a scarce resource, bandwidth. In cognitive vehicular networks unlicensed secondary users use any spectrum channel based on primary user activity on the channel and to find out traffic on a spectrum band, the secondary users have to rely heavily on spectrum sensing. Most of the existing research on spectrum sensing was conducted considering secondary users to be stationary, thus avoiding consequences of mobility of secondary users on the performance of spectrum sensing to some extent. In a highly dynamic cognitive vehicular network the vehicles are assumed to be equipped with cognitive radio for spectrum sensing and they play the role of secondary users. To acquire information about more realistic nature of spectrum sensing and to predict the network behavior in practical scenarios, we scrutinize the combined impact of the mobility of secondary users and primary user activity on the performance of spectrum sensing in highly dynamic cognitive networks. Our main contribution in this paper is to investigate the change in nature of three important performance metrics of spectrum sensing such as probability of miss detection, probability of false alarm and expected transmission time with respect to mobility of secondary users. The mathematical model used in this paper considers velocity of secondary users, activity of primary users, initial distance between primary and secondary users and their transmission ranges. Numerical results procured from various simulation of the mathematical model are presented to make the analysis meaningful. It is noted that mobility of secondary users has a significant impact on probability of miss detection and expected transmission time, but probability of false alarm shows almost neutral behavior to mobility of secondary users

The impact of secondary user mobility and primary user activity on spectrum sensing in cognitive vehicular networks

© 2015 IEEE. In cognitive vehicular networks, unlicensed secondary users heavily depend on spectrum sensing to find unused spectrum bands for communications. The performance study of existing spectrum sensing algorithms often overlooks the impact of secondary user mobility.Many of them assume secondary users stationary or with low mobility. In this paper, we investigate the joint impact of secondary user mobility and primary user activity on spectrum sensing for highly dynamic cognitive vehicular networks. We assume that each vehicle is equipped with a cognitive radio for spectrum sensing. The main contribution of this work is to investigate mathematical models for missdetection probability and expected overlapping time duration for spectrum sensing. The proposed method incorporates velocity of secondary user, activity of primary user, initial distance between primary and secondary users and their transmission ranges. In ordered to corroborate the analysis, numerical results obtained from simulations are presented. It is noted that the speed of the vehicular secondary user and the activity of primary user have significant impact on miss-detection probability, but not on false alarm probability. Furthermore, transmission range, velocity and initial separation distance have huge impact on expected overlapping time duration

Performance analysis of secondary users in the presence of attackers in cognitive radio networks

© 2015 IEEE. Cognitive radio network is regarded as an emerging technology to solve \u27spectrum scarcity\u27 through dynamic spectrum access to support exponentially increasing wireless subscriptions. However, spectrum sensing and dynamic spectrum sharing in cognitive radio network invite more security attacks making security as one of the main concerns. In this paper, we analyze the performance of the secondary users in terms of physical-layer security in the presence of both eavesdroppers and jammers in cognitive radio networks. In this case, secondary users not only have to compete against eavesdroppers and jammers (who are trying to reduce the secrecy rates of secondary users) but also have to compete with other secondary users to gain access to idle channels to gain high secrecy rates. The main contribution of this work is to investigate game theoretical model to maximize utility of secondary users in the presence of eavesdroppers and jammers. The proposed approach can be particularized to a scenario with eavesdroppers only or jammers only while evaluating the performance of secondary user physical layer security. Performance of the proposed approach is evaluated with the help of numerical results obtained from simulations and the proposed approach outperforms other existing methods. Furthermore, there is sever impact on utilities (secrecy rates) of secondary users when both eavesdroppers and jammers are active in the network

Modelling PET Radionuclides Production in Tissue and External Targets Using Geant4

The Proton Therapy Facility in TRIUMF provides 74 MeV protons extracted from a 500 MeV H⁻ cyclotron for ocular melanoma treatments. During treatment, positron emitting radionuclides such as C-11, O-15 and N-13 are produced in patient tissue. Using PET scanners, the isotopic activity distribution can be measured for in-vivo range verification. A second cyclotron, the TR13, provides 13 MeV protons onto liquid targets for the production of PET radionuclides such as F-18, N-13 or Ga-68, for medical applications. The aim of this work was to validate Geant4 against FLUKA and experimental measurements for production of the above-mentioned isotopes using the two cyclotrons. The results show variable degrees of agreement. For proton therapy, the proton-range agreement was within 2 mm for C-11 activity, whereas N-13 disagreed. For liquid targets at the TR13 the average absolute deviation ratio between FLUKA and experiment was 1.9±2.8, whereas the average absolute deviation ratio between Geant4 and experiment was 0.6±0.4. This is due to the uncertainties present in experimentally determined reaction cross sections