Performance Optimization And Analysis For SWIPT Networks With Nonlinear Characteristics Of Energy Harvesting Circuit

With the promotion of informatization,intelligence and the 5th generation mobile networks(5G)of human society,wireless energy-constrained networks such as the Internet of Things(Io T),wireless sensor networks(WSN),and wireless wearable networks will be rapidly developed and deployed.The number of terminals and data demand will show exponential growth,which puts forward higher requirements for the capacity,reliability,coverage,and energy efficiency of the wireless network system.In addition,due to the limited energy carried by network nodes,it is difficult to ensure long-term continuous operation,which has become a major bottleneck restricting large-scale network deployment.Therefore,how to reduce the energy consumption of the network and extend the working time of the network while ensuring the energy supply of network nodes and the effective transmission of network information is an important issue.To solve this problem,the continuous development and evolution of advanced wireless communication technologies,such as multi-antenna technology and relay technology,can be used to reduce node energy consumption and improve network energy efficiency and spectrum efficiency;On the other hand,energy harvesting(EH)technology,which harvests renewable energy or reusable energy from the surrounding environment,can provide continuous power supply for network nodes.Therefore,combining wireless information transfer and wireless energy transfer technology,studying the system performance of wireless communication networks plays an extremely important role in promoting the practical application of EH in wireless energy-limited networks.Under the nonlinear EH model which matches the characteristics of practical EH circuit very well,the performance optimization and analysis of simultaneous wireless information and power transfer(SWIPT)networks in the non-mobile and mobile scenarios of Io T.In the non-mobile scenarios,the users are homogeneous to heterogeneous,and the network topology is from single-hop to multi-hop,where the transmission power minimization problem and outage performance of the system are explored respectively.In the mobile scenarios,the information-energy region and network coverage are studied respectively from the ground to the air movement.The novelties and contributions of the dissertation include:1)The optimal power minimization design of SWIPT networks is investigated under nonlinear EH model.An optimization problem is formulated to minimize the transmit power subject to the required signal-to-interference-plus-noise ratios(SINR)constraints at information-energy receivers(IERs)and information receivers(IRs),and the harvested energy constrains at IERs and energy receivers(ERs),by jointly optimizing the beamforming vector and the PS ratios at IERs.Since the problem is nonconvex,the semidefinite relaxation(SDR)and variable substitutions are used to handle it.For some cases,it theoretically prove that the globe optimal solution can be guaranteed by using proposing method,and for rest cases,we discuss its optimality via simulations.Numerical results show that although the traditional linear EH model is feasible for the practical EH circuits in some cases,the corresponding system consumes more transmit power than that under the non-linear model EH.2)The SWIPT network with coexisting power-splitting users(PSUs)and timeswitching users(TSUs)is studied under the nonlinear EH model.An optimization problem is formulated to minimize the transmit power subject to users' information rate and harvested energy constrains by jointly optimizing the transmit beamforming vectors,PSUs' PS ratios and TSUs' TS factors.A two-layer algorithm is first presented based on SDR and it is theoretically proved that the global optimum is achieved.Also,a successive convex approximate-based(SCA-based)algorithm is proposed as an alternative,which is able to find the near-optimal solution with low complexity by using the first-order approximation.Numerical results show that with the same EH requirements,TSUs are more likely to enter into the saturation region compared with PSUs,but their EH efficiency is higher than that of PSUs.It is also shown that the minimal required transmit power under the nonlinear EH model is much lower than that under the linear one.After the saturation point of the nonlinear EH model the linear one yields a lower required transmit power,but the corresponding result is fake.3)The system outage probability for SWIPT communication networks is investigated with the nonlinear EH model and imperfect channel state information(CSI).the closed-form expressions of the system outage probability and reliable throughput are derived.In order to provide more concise results,the corresponding approximate expressions are also derived at low and high signal-to-noise ratio(SNR).Numerical results show that our obtained theoretical results match Monte Carlo simulation results very well,demonstrating the effectiveness of our obtained analytical results.Besides,it also shows that the imperfect CSI of the source-to-relay link has greater impact on the system performance than that of the relay-to-destination link.Additionally,by using the nonlinear EH model,the false performance caused by the linear EH model can be reduced.4)The information-energy(I-E)region for SWIPT networks is studied in mobility scenarios.In order to characterize the tradeoff between the received information and harvested energy,the I-E region is defined,and corresponding optimization problems are formulated.To efficiently solve the nonconvex optimization problem with the logistic nonlinear EH model,SCA-based algorithm is proposed,which is able to characterize the lower bound of the I-E with low complexity.To solve the optimization problems with the linear and piecewise EH models,some closed and semi-closed solutions are derived by using Lagrange dual method and KKT conditions.Numerical results show that compared with the I-E regions under the linear and piecewise EH models,that under the logistic nonlinear EH model is smaller.Moreover,with a fixed moving speed,when the transmit power is relatively large,the logistic nonlinear EH model can be replaced with the piecewise one due to the relatively small gap between their achieved I-E regions.Additionally,for a fixed moving track length,the higher moving speed yields the smaller I-E region with all three EH models.5)The information and energy coverage probabilities of unmanned aerial vehicle(UAV)-enabled SWIPT networks is investigated under the nonlinear and linear EH models.By using stochastic geometry approach,the general and explicit expressions of the information delivering,the harvested energy and joint information and energy coverage probabilities are derived,respectively.Numerical results show that compared to the nonlinear EH model,the bias of the analyzing results caused by the linear EH model is obvious,and although the nonlinear EH model yields a lower coverage probability than the linear one,it avoids the false output caused by the linear one.Moreover,the nonlinear EH model has the greater impact on the harvested energy coverage probability of the TS-based system than on that of the PS-based one.But,the coverage performance with PS-based system is superior to that with TS-based one.