Research On Resource Management And Security Strategy Of D2D Communications In Cellular Networks

Technology always grows in continuous revolutions.In the past few decades,mobile communication systems have rapidly evolved from the first generation(1G)mobile communication technology to the 5th generation(5G)mobile communication technology that has been deployed on a large scale,and then to the 6th generation(6G)that is currently being explored in many countries,the mobile communication technology has become the commanding height of the scientific and technological competition in all countries of the world.The law of technological development determines that the standards for each generation of communications technology always take a long time to mature.Although 5G has already been used commercially,the continuous evolution from non-standalone(NSA)to full standalone(SA)still needs some time,and different applications for the three scenarios of enhanced mobile broadband(eMBB),ultra reliable low latency communication(uRLLC),and massive machine type communication(mMTC)are still being improved continuously.Therefore,5G related technologies will continue to be the focus of attention by scholars and the industry.Nowadays,the wireless communication is rapidly shaping a future that will be expanded by billions of devices,the future smart city will be mainly driven by the seamless connection of wireless devices,the number of intelligent terminal devices will continue to increase rapidly,and the data business carried by mobile communications is growing exponentially,while wireless spectrum resources are increasingly overcrowded.Therefore,how to effectively improve network capacity and wireless spectrum utilization is of utmost importance in communication technology research.As one of the key technologies of 5G,device-to-device(D2D)communication has its unique structure and topology,in which devices close to each other can communicate by reusing spectrum resources in a peer-to-peer manner without passing through a base station(BS)or the core network.Due to D2D technology allows reusing cellular network frequencies in licensed frequency bands,D2D can improve the spectrum efficiency of the system while providing customers with communications services of higher quality.Moreover,the distance of D2D communication is relatively short and the channel quality tends to be higher,with higher transmission rate,lower delay and power consumption.D2D communication can not only improves energy efficiency,but also increases the battery life of the equipment.In addition,D2D supports more flexible network architecture and connection methods,which can improve link flexibility and network reliability,increase system throughput and fairness,and enhance user experience and network business expansion capabilities.However,only relying on a single technology can no longer meet the extremely high performance requirements of 5G and beyond.More researchers combine D2D technology with Multiple-Input Multiple-Output(MIMO),millimeter-Wave(mmWave),Non-Orthogonal Multiple Access(NOMA),Full Duplex(FD)and other technologies in different scenarios by exploiting their merits to meet the business requirements under different scenarios.Aiming at the shortage of spectrum resource and network security problems caused by the rapid development of smart devices and data centers,this thesis mainly focuses on the resource management and security strategy of D2D communication in cellular network.Firstly,a transmission scheme of NOMA-based D2D adaptive relaying in cellular downlink communication is designed,which effectively improves the sum throughput of the system.Secondly,power allocation method in NOMA-based D2D communication is optimized to maximize the achievable rate of the D2D group with the imperfect Successive Interference Cancellation(SIC),and the impact of different degrees of SIC on the system performance is analyzed.Then,based on the same system model,the physical layer security of D2D communication under passive eavesdropping is studied,and an optimal power allocation strategy satisfying the maximization of system secrecy rate is proposed.Finally,considering the social security factor in practical communications,the problem of secure relay selection based on social network in large-scale cellular network is investigated.The main research results of the thesis are as follows:1.A scheme of NOMA-based D2D adaptive relaying and transmission in the cellular downlink network is proposed.Considering that all the cellular and D2D users have SIC capabilities,a two stage NOMA-enabled D2D assisted cellular communication scheme in relay mode is designed.In the first time slot,the BS can transmit signal both to the near cellular user and to the transmitter and the receiver of a D2D pair simultaneously.Next,in the second time slot,the D2D user acts as a relay,one user of the D2D pair will be adaptively selected as a relay to forward the signal of the BS to the far cellular user,and at the same time,the D2D transmitter can send its data to the D2D receiver.Meanwhile,the near cellular user can perform SIC decoding again after receiving the relay signal from D2D user,which can improve the spectral efficiency of the system.The operation of the D2D transmitter and receiver in each time slot will be processed separately according to the different decoding state.The system throughput is analyzed,and simulations are carried out to reveal the effect of key parameters on the system throughput.Simultaneously,a benchmark transmission scheme is designed,and the simulation comparison shows that the proposed method significantly improves the total throughput of the system.2.A power allocation optimization strategy of D2D group communication in cellular network is proposed,in order to solve the power allocation problem in the case of the NOMA system with imperfect SIC.Aimed at the D2D group communication model based on NOMA in the uplink cellular network with imperfect SIC,the problem of maximizing the sum achievable rate of the D2D group is established under the constraints of Quantity of Service(QoS)limitation of cellular users and the transmitting power of D2D users.To obtain an effective solution,by utilizing the Karush-Kuhn-Tucker(KKT)condition,the subgradient method are used to update the Lagrangian multiplier and perform the optimal power allocation of the system.Simulation results show that the proposed power allocation scheme obviously improves the achievable rate of the system compared with the two benchmark schemes of NOMA based on average power allocation and OMA.At the same time,the impact of imperfect SIC parameters on the achievable rate of the proposed strategy is analyzed by simulation,and the importance of SIC decoding in NOMA technology is verified.3.Aiming at the physical layer security problem in NOMA-based D2D cellular network,an optimal power allocation scheme is proposed to maximize the security rate of D2D group communication system.Building on the network model of the previous research work and considering the physical layer security of D2D group communication with passive eavesdropping,the secrecy rate maximization problem of the D2D group is established under the constraints of the QoS limitation of each D2D user and the total transmission power of D2D group.According to the KKT condition,the closed-form solution of the optimal power allocation in the two causes are derived,and the final optimal power allocation strategy is obtained by comparing the total secrecy rate of the D2D communication system in the two cases.Compared with NOMA scheme based on Fractional Transmit Power Allocation(FTPA)and OMA scheme,the proposed strategy has the highest secrecy rate and energy efficiency.4.Considerilg the actual communication scenarios of large scale cellular networks,a secure relay selection scheme for D2D communication based on social network is proposed.In this thesis,a relay candidate region based on the maximum communication distance of D2D is defined.Considering the scenario in which the BS and all users are subject to the Poisson distribution in a large scale cellular network,the closed expressions of the outage probability of D2D link without relay and relay-assisted D2D link are derived respectively by using the Poisson Point Process(PPP)method.Next,a social network system model is established,and the security evaluation factor is designed based on the social relationship among users.Then a secure relay selection scheme in the defined relay candidate region of the D2D communication system based on social network is proposed,which has a better secure performance compared with the designed distance-based relay selection method.