Research On Cooperative Relay Networks Based On RF Energy Harvesting And Rateless Codes

In the past decades,wireless communication has made a rapid progress.With the development of the society,the people put forward higher requirements for wireless com-munication systems.On one hand,the people wish to obtain higher rate communication services.On the other hand,the people also start to focus on energy constrained network-s,such as wireless sensor networks,Internet of Things,where wireless devices cannot be connected to the power grid and are hard to frequently recharge/replace the batteries.For these networks,the focus is how to obtain stable and sustainable energy supply to pro-long the networks’ lifetime as much as possible in the premise of basic communication services.Cooperative relay technique has abstracted much attention due to its advantages,such as the communication efficiency improvement and coverage extension.The research of this thesis is based on cooperative relay networks.In order to satisfy the requirement of longer lifetime for cooperative relay networks,radio frequency(RF)energy harvesting techniques,including wireless powered communication networks(WPCN)and simulta-neous wireless information and energy transfer(S WIPT),are adopted to supply the energy for the energy-constrained communication nodes in the networks.In addition,in order to improve the networks’ communication quality,rateless codes(fountain codes)are adopt-ed to enhance the performance for cooperative relay networks,which have the advantages such as forward error correction,adaption to channels and little feedback.The thesis com-bines these techniques in order to satisfy the requirements of the development of future communication and main contributions are summarized as follows.Firstly,the strategy design and optimization are investigated for WPCN-based us-er cooperation networks.For energy-constrained two-user cooperation networks,power station is deployed to supply energy for users and energy beamforming is adopted to en-hance the energy transfer efficiency.To explore the system performance limit,weighted sum rate is maximized by jointly optimizing the energy beamforming design and time al-location.Moreover,for give amounts of data required to be delivered at the two users,an optimization problem is formulated to minimize the system total transmission time.Be-cause of the non-convexity of the problems,we propose efficient methods to solve them by using some proper variable substitutions and semidefinite relaxation(SDR).We the-oretically prove that the global optimum can be guaranteed with our proposed methods.Simulation results show that system performances can be significantly enhanced by using the proposed methods.Besides,compared with direct transmission without user coop-eration,when the distance between two users is nearer,user cooperation transmission is superior to direct transmission.Secondly,the strategy design and optimization are investigated for SWIPT-based OFDM cooperative relay networks.For two-hop OFDM relay network with energy-constrained relay node,two kinds of PS receivers(IPS and DPS receivers)are studied for the OFDM relay system,and their system achievable information rates are given.Further,in order to explore the performance limits of the system,two optimization problems are formulated to maximize the achievable rates by jointly optimizing the resource allocation.Since the problems are non-convex and hard to deal with,based on theoretical analysis,for IPS receiver and DPS receiver,two-step and three-step optimization algorithms are re-spectively proposed to solve them.Results show that the proposed algorithms can reach the maximal achievable information rates of two kinds of receivers,and IPS receiver is of higher achievable information rate while DPS receiver is of lower computational com-plexity.In addition,results also show that to achieve better system performance,in the SWIPT-enabled two-hop OFDM relay system,the relay node should be deployed near the source,while in conventional non-SWIPT system,the relay should be deployed at the midpoint of the line between the source and the destination.Thirdly,the strategy design and optimization are investigated for SWIPT and rate-less codes-based cooperative relay networks.For rateless coded cooperative relay net-work with energy-constrained relay node,three SWIPT relaying protocols,namely,ideal protocol,PS protocol and TS(Time Switching)protocol,are presented,and two informa-tion receiving methods,namely,information accumulation and energy accumulation,are considered.The achievable information rate are given for the three protocols.In order to explore the system performance limits with these three protocols,three optimization problems are formulated to maximize their achievable information rates and efficient al-gorithms are proposed to solve the problems.For the ideal protocol,explicit expressions of the optimal solutions are derived.For the PS protocol,a linear-search algorithm is designed to solve the non-convex problems.For the TS protocol,an efficient method is proposed by deriving the relation among the optimized variables.Results show that with the same SWIPT protocol,the system performance of information accumulation receiving method outperforms energy accumulation receiving method,while with the same infor-mation receiving method,PS protocol outperforms TS protocol.Moreover,compared with SWIPT relay systems without rateless codes,the performance can be enhanced by deploying rateless codes.Besides,it is shown that when the relay node is deployed near the source,the best achievable rate performance is reached.Finally,the strategy design and performance are investigated for rateless codes-based cooperative relay networks.Different from the aforementioned work based on RF energy harvesting,the network without RF energy harvesting is studied in this part.(1)For rate-less coded cooperative multi-relay networks,the effect of the channel orthogonality on the system performance is studied,and the probability density functions of achievable infor-mation rate and average information rate are derived by applying the probability theory.Results show that the non-orthogonality of channels significantly decreases the achiev-able rate of rateless coded cooperative relay system.(2)For wireless butterfly networks,the combination of rateless codes and network coding is investigated,fountain network coding(FNC)protocol is proposed and the throughput performance is analyzed by ap-plying the probability theory.Results show that compared with non-coding protocol and conventional opportunistic network coding protocol,the throughput can be enhanced by the FNC protocol.