Performance Analysis And Optimization For PS-SWIPT Based Relay Networks

Wireless sensor networks(WSNs)have been one of important parts of Internet of things(Io T).In WSNs,the application of relaying technology is able to greatly improve the reliability of information transmission among sensor nodes.However,a great number of researches on relaying enabled WSNs are based on the assumption that the relay nodes consume theirself energy to assist the sensor nodes to achieve information transmission.In practice,the relay nodes are usually powered by its battery and the equipped battery's capacity is very small,which greatly shortens the operation time of the relay nodes and may lead to network paralysis.Therefore,how to provide stable and enduring energy for relay nodes at a low cost while ensuring the required communication quality of service(Qo S)is particulary important in relaying enabled WSNs.In this context,radio frequency(RF)enabled wireless power transfer is proposed and recognized as one of promising solutions for this problem and is receiving much attention.Since RF signals can carry energy and information simultaneously,the WPT and the relaying technology can be naturally linked together,yielding a simultaneous wireless information and power transfer(SWIPT)enabled relay network that can prolong the operation time of the relay nodes while satisfying Qo S.In the researches of SWIPT enabled relay networks,the relay node uses either power splitting(PS)scheme or time switching scheme to divide the received signals into two parts: one part for energy harvesting(EH)and the other part for information processing.It has been shown by the existing works that PS scheme is able to realize a better transmission performance than the TS scheme in general.Motivated by this observation,this thesis aims to study the decode-and-forward(DF)PS-SWIPT enabled relay networks,where we mainly focus on the design of PS enabled transmission scheme and investigate the achievable transmission performance.Our main contributions are summarized as follows.1.Research of PS-SWIPT enabled dual-hop DF relaying without direct linkMost of existing works on SWIPT enabled DF dual-hop relaying without direct link assume that the transmission time between the source node and the relay node equals that between the relay node and the destination node(a special time allocation scheme).However,the fixed time allocation in DF relaying leads to non-efficient use of time and power resources.Inspired by this observation,we propose a joint transmission time allocation(TA)and PS enabled transmission scheme to improve the transmission performance of the DF relay networks.Compared with the existing scheme with equivalence transmission time for dual-hop,the proposed scheme can exploit an extra dimensional resource,i.e,transmission time allocation,and achieve a better transmission performance.On this basis,we design optimal static and dynamic transmission schemes of joint time allocation and power splitting to conduct the relay in terms of outage performance and ergodic performance,respectively.With the knowledge of statistic channel state information(CSI),we derive the analytical expressions for the outage probability and ergodic capacity,which are used to evaluate the transmission performance and to determine the optimal static PS and TA ratios.With the knowledge of instantaneous CSI,we formulate two joint optimization problems to minimize the outage probability and maximize the instantaneous channel capacity by optimizing the TA and PS ratios,respectively.For the problem to minimize the outage probability,we firstly transform the original problem into a convex one dimensional optimization problem,and propose a low complexity iterative algorithm to solve this problem.For the problem to maximize the ergodic capacity,we firstly introduce a slack variable to remove the min function.Then we prove that the problem is convex and propose a block coordinate descent enabled iterative algorithm to obtain the optimal solutions.Finally,computer simulation verify the advantages of the proposed schemes over the existing peer schemes.2.Research of PS-SWIPT enabled dual-hop DF relaying with direct linkAccording to whether the received signal in the first transmission phase is used for decoding or not,we propose two transmission schemes for the PS-SWIPT enabled DF relay network.The main works are as follows.(a)When the relay node works in the energy harvesting(EH)and information decode(ID)modes simultaneously in the first transmission phase,we study the PS enabled transmission scheme that consists of two equal transmission phases for the SWIPT enabled dual-hop DF relay network with direct link,and aim to design the optimal static and dynamic PS ratios,respectively.For the case only with statistic CSI,we derive the expression for the outage probability with a given static PS ratio,which exhibits that there exists an optimal static PS ratio within the interval [0,1].Besides,we derive the achievable diversity gain of the considered network,which shows that the proposed static PS scheme can achieve the full diversity gain.When the instantaneous CSI is available,we firstly derive a closed-form expression of the optimal dynamic PS ratio to minimize the outage probability.The outage probability with the optimal dynamic PS scheme is further obtained to evaluate the performance of the considered relay network and provide insights on the achievable diversity gain.Finally,computer simulations are provided to validate the derived expressions and compare static and dynamic PS enabled transmission schemes in terms of outage probability.(b)When the received signal in the first transmission phase is only used for EH,we propose a joint of TS and PS enabled transmission scheme.In the proposed transmission scheme,a whole transmission block is divided into three parts,among which the second and the third transmission phases are equal.In order to explore the advantages of the proposed scheme,we formulate an optimization problem to maximize the system capacity by optimizing the TS and PS ratios.As this problem is non-convex,we convert it into two subproblems by means of the inequality relation between the signal noise ratios of source-relay link and relay-destination link.We derive the explicit results for the first subproblem,and propose an alternative iterative algorithm to obtain the optimal solution of the second subproblem.By combining the solutions from two subproblems,we further propose a low complexity iterative algorithm to determine the optimal solutions.Simulation studies show that the proposed transmission scheme achieves a higher system capacity than the existing protocols.3.Research of SWIPT enabled two-way DF relay networks with TDBCAlthough some works on the SWIPT enabled two-way DF relaying with time division broadcast(TDBC)have been studied,two drawbacks still exists.One is that the relay node usually adopts the same PS ratio to process the signals transmitted by the both terminals.The other is that the relay node does not optimize the power allocation ratio to combine the decodes two signals transmitted by both terminals.The above observations lead to the non-efficient use of the received signals due to the asymmetric instantaneous CSI between the relay node and the two terminals.Motivated by this,we propose a joint of asymmetric PS and power allocation enabled transmission scheme to conduct the relay node,and study their transmission performance in terms of system outage probability.When the statistic CSI is available,we derive the expressions for the system outage probability to evaluate the transmission performance of the proposed static transmission scheme.Then we investigate the impacts of system parameters,e.g.,the asymmetric PS ratios,the power allocation ratio,etc,on the achievable system outage probability.Besides,we study the proposed dynamic transmission scheme with the knowledge of instantaneous CSI.In particular,we formulate an optimization problem to minimize the system outage probability by optimizing the asymmetric PS ratios and the power allocation ratio at each transmission block.Employing the property of DF relaying and information causality,we obtain the closed-form expressions for the asymmetric PS ratios and the power allocation ratio.With the obtained optimal solutions,the system outage probability is further derived.Finally,computer simulations validate the correctness of the derived expressions and the advantages of the proposed static and dynamic transmission schemes over the existing schemes in terms of system outage probability.The main contributions of this thesis is to propose several PS enabled transmission schemes for SWIPT enabled one-way DF relay networks and SWIPT enabled two-way relay networks with TDBC.Our studies have validated that the proposed schemes achieve a better transmission performance compared with the existing ones,and have provided theoretical base for the application of SWIPT enabled relay networks in the practical communications.