Research On Multi-relay SWIPT Based On OFDM

From the emergence of mobile phones to the mobile internet that permeates every corner of people's lives,every innovation in wireless communication technology has profoundly changed society.With the official arrival of the 5G era,wireless communication networks have higher transmission rates,lower delays,and greater system capacity,and will become an important driving force for future economic development and social progress.However,with the rapid increase in the number of users,the energy consumption of communications has also increased geometrically,and the problem of energy supply shortage has become increasingly serious.Simultaneous Wireless Information and Power Transfer(SWIPT)technology utilizes Radio-Frequency(RF)signals to achieve the parallel transmission of information and energy,provide a stable source of energy for equipment,and provide a new solution to the energy problem of wireless communication networks.SWIPT technology mainly uses three modes: Power Splitting(PS),Time Switching(TS)and Antenna Selecting(AS).However,these three modes require the receiver to be equipped with a distributor,which will increase the complexity of the system design and the implementation cost.In order to solve this problem,we further combine Orthogonal Frequency Division Multiplexing(OFDM)technology to realize the coordinated transmission of energy and information through subcarrier allocation.With the background of the multi-relay SWIPT network,this dissertation combines OFDM technology and relay cooperative technology to further improve system performance.The main work and achievements of this dissertation are as follows:(1)In order to solve the problem that the current multi-relay SWIPT method requires a receiver to be equipped with a distributor,we first propose a one-way multi-relay Decode-and-Forward(DF)SWIPT method based on OFDM.In this method,we divide the transmission time into two timeslots.In the first timeslot,the source node transmits the signal to relay nodes.Relay nodes use SWIPT technology to allocate a part of the subcarriers for information decoding and the rest for energy reception.In the second timeslot,relay nodes use the energy harvested for forwarding signals without the need for additional energy supply.However,in this method,the relays need to decode the received signal,and cannot guarantee the security of the information.In the AF protocol,the relays amplify the signal linearly and forward it,thereby improving the security of the system's transmission.Therefore,we propose a one-way multi-relay AF-SWIPT method based on OFDM,and consider the case where there is a direct transmission channel between the source node and the target node.We jointly optimize the subcarrier and power allocation in the above two methods in order to obtain the maximum information transmission rate.Simulation results show that compared with other algorithms,the two optimization methods proposed can obtain higher information transmission rate.(2)In order to further improve the spectrum utilization of the relay-SWIPT network,we propose two bidirectional multi-relay SWIPT methods based on OFDM.In these two methods,relay nodes receive signals from two source nodes in the first timeslot and then allocate a part of the subcarriers for decoding and the remaining subcarriers for harvesting energy.In the second timeslot,relay nodes use the harvested energy to assist in signal forwarding,so there is no need to provide additional energy.Both source nodes receive the broadcast signal from relay nodes.Specifically,we study the bidirectional multi-relay SWIPT method based on DF and AF protocols respectively.We maximize the information transmission rate of the system by jointly optimizing the subcarriers and power allocation.Simulations show that the two optimization methods proposed can achieve higher information transmission rates than other schemes.