Research On Highly Energy-efficient Cooperative Jamming Strategy For Cognitive Radio-enabled Internet-of-Things

The Internet of Things(IoT)has become the third wave of information industries development following computers and Internet,and mobile communications.It is regarded as a major strategic industry by many countries in order to seize the commanding ground of the new round economic development.IoTs will be widely applied into many fields,such as Internet of vehicles,smart grids,smart home networks,security monitoring systems,mobile payment systems,smart wearable devices,remote telemedicine networks,and intelligent manufactering systems,etc.Because of these potential applications,the number of IoT equipment worldwide has reached 22 billion by the end of 2018 and is predicted to be 50 billion by 2030.However,the current limited spectrum resource is far from enough to meet the access requirement of such a massive number of devices.To solve this problem,researchers have applied cognitive radio(CR)technique into IoTs,which can improve spectrum utilization via dynamic spectrum alloaction.Thus,the CR enabled IoT(CR-IoT)has been a hot topic in recent years.The security of CR-IoTs is a research highlight because legitimate signals are vulnerable to eavesdropping due to the openness and the broadcasting characteristics of wireless channels.In order to prevent eavesdropping,encryption-based cryptography algorithms have been employed in the network layer.However,they are not suitable for lightweight CR-IoT devices due to high computing overheads.Thus,researchers have proposed the physical layer security technique.Especially,cooperative jamming based physical layer security strategies have been widely studied in cognitive radio networks(CRNs).Specifically,jamming signals are transmitted to reduce eavesdropping channel conditions so as to prevent eavesdroppers from demodulating received legitimate signals and guarantee security of the legitimate information.However,current research work has the following limitations when applied into the CR-IoT: 1)Due to the need of traversing all condiate nodes,traditional jammer selection strategies are of high time cost when directly applied to the CR-IoT with a large number of nodes;2)Current energy harvesting based physical layer security schemes employ the time switching mode or the power splitting mode,where the correlation between the time proportion and the power proportion parameters was neglected.Therefore,there is a need to jointly optimize these two parametes for improving the system performance;3)The typical continuous cooperative jamming strategies are not applicable to energy-constrained CR-IoT because the security of the legitimate transmission may not be ensured due to the insufficient energy of jammers.Motivated by aforementioned challenges of combating eavesdropping in CRIoTs,this dissertation studies the highly energy-effcient cooperative jamming based physical layer security on the basis of theories such as the optimal stopping theory,mathmatic modeling and optimization algorithms.It investigates the problems of reducing the time cost of jammer selection,improving the energy-harvesting performance,and decreasing the energy cost of jammers.The main contributions of this dissertation are concluded as follows:1)To quickly select a suitable friendly jammer from a large number of candiate nodes,an optimal stopping theory based jammer selection(OSJS)strategy is proposed for the scenario of a single eavesdropper.In this strategy,a novel security metric,denoted as the secrecy goodput,is employed as a threshold to determine stopping conditions.Then,for the scenario of multiple eavesdroppers,a random jammer selection scheme is employed to quickly select multiple jammers,whose beamforming vectors are jointly optimized to meet the security requirement.Extensive simulation experiments demonstrate the proposed schemes can strike balance between the time overhead and the security performance.2)An energy harvesting scheme with a time-power-splitting mode is proposed to effectively supply energy for CR-IoT devices so as to support secure communications in CR-IoTs.Specifically,a simultaneous information and energy transfer scheme is designed for the two-way relay CR-IoT.Under constraints of the harvested energy of both the relay and jammer,the time-switching parameter and the power-splitting paramter are jointly optimized to maximize the system throughput for the case without any eavesdropper and the secrecy throughput for the case of a single eavesdropper.Meanwhile,the beamforming vectors of the relay and jammer are designed to meet the requirement of reliable and secure communication.Simulation experiment results demonstrate the proposed schemes can avoid communication interruption caused by the insufficient energy of the relay and jammer,and thus guarantee sustainable secure communications.3)An intermittent jamming strategy(IJS)is proposed for a typical CR-IoT secure communication scenario.Under the IJS,the jammer alternates between jamming and non-jamming modes during the legitimate transmission.The feasibility of the IJS is verified by solving the optimizing problem with respect to jamming duration proportion and jamming power.Then,on the basis of transmit frame formate,the cross-layer design of detailed IJSs is proposed.They are optimized from three aspects including jamming power,jamming method,and jamming positions.Extensive experiments demonstrate the proposed IJSs can effectively degrade the reception of the eavesdropper and outperform the widespread continuous jamming scheme(CJS)when available jamming energy is limited.