Research On Energy Efficiency Optimization And Physical Layer Security In SWIPT System

Simultaneous wireless information and power transfer(SWIPT),as a promising energy harvesting technique,has recently drawn significant interests from both academia and industry.The main idea of SWIPT is to enable mobile device with finite battery capacity to supply both information decoding and energy harvesting at the same time,which can significantly enhance performance of mobile device.With wireless sensors and transceivers getting ever smaller and more energy-efficient,it is expected that SWIPT technique will be widely applied in the design of distributed mobile terminals,such as rechargeable sensors in harsh environments,wearable smart devices,smart phone and so on.However,with the advent of the mobile Internet Era,the exponential increase of mobile devices connected to Internet and enormous energy demand put forward higher requirement for energy efficiency of wireless communication network.Besides,the energy receiver closer to the transmitter,can more easily decode and eavesdrop intended information sent to the information receiver due to the open and broadcast nature of wireless radio signal.Therefore,this gives rise to the physical layer security issue of SWIPT system.With the development of SWIPT technique,the research on energy efficiency optimization and physical layer security problem has important practice and application value.Based on the state of art research results,this dissertation mainly focuses on energy efficiency optimization and physical layer security problem in SWIPT system.The main work and contributions are summarized as follows:1.Energy efficiency optimization of transceiver design is studied for SWIPT system in Wireless Rechargeable Sensor Networks(WRSNs).From a green communication perspective,the tradeoffs between energy efficiency and spectral efficiency,energy throughput efficiency and outage target rate for two different modes,i.e.,power splitting(PS)and time switching modes(TS)are considered.Moreover,the energy efficiency maximization problem subject to the constraints of minimum Quality of Service(QoS),minimum harvested energy and maximum transmit power is formulated as a non-convex optimization problem.In particular,the optimal power control and power allocation policy for PS and TS modes are proposed to maximize energy efficiency of data transmission.For PS and TS modes,the corresponding suboptimal iterative algorithms are proposed to solve the non-convex optimization problem by taking into account the circuit power consumption and the harvested energy.Besides,the closed-form expressions of the outage probability and energy throughput efficiency are derived in the case that the transmitter does not or partially know the channel state information(CSI)of the receiver.Simulation results illustrate that the proposed optimal iterative algorithms can rapidly converge within a small number of iterations and the tradeoffs can be achieved between energy efficiency and spectral efficiency,energy throughput efficiency and outage target rate,respectively.2.The optimization problem of target secrecy rate and power allocation ratio is studied on the basis of secrecy outage probability and effective secrecy throughput in the SWIPT system over fading wiretap channel.Firstly,the closed-form expressions of secrecy outage probability and effective secrecy throughput are derived for On-off and adaptive secrecy transmission modes.Moreover,the effective secrecy throughput maximization problem is formulated under the reliability constraint in the on-off and adaptive transmission modes,and the closed-form optimal solutions of power allocation ratio and target secrecy rate are proposed.Finally,numerical results illustrated the effect of system parameters on secrecy outage probability and effective secrecy throughput,such as target secrecy rate,power allocation ratio and average gains of main channel and eavesdropper channel.3.Secrecy energy efficiency maximization(SEEM)problem is studied for two-user OFDMA networks with SWIPT.Firstly,power splitting scheme is adopted by each user,which would split received radio frequency(RF)signals into two independent parts for information decoding and energy harvesting,respectively.Besides,taking both the individual secrecy Quality of Service(SQoS)requirement and the individual harvested energy constraint into consideration,the SEEM problem is formulated as a nonlinear fractional programming problem.Moreover,according to Dinkelbach's method,a power allocation and power splitting(PAPS)algorithm is proposed by solving the equivalent convex optimization problem.Finally,numerical results verify and analyse the impact of static circuit power consumption,maximum transmit power,power splitting ratio,subcarrier bandwidth and path loss on secrecy energy efficiency of our PAPS algorithm.