Researches On Simultaneous Wireless Information And Power Transfer Based On Resource Allocation In OFDM Systems

Wireless sensor networks(WSNs)are extensively applied in various fields with its characteristics of low power consumption,low cost,distribution and self-organization.Traditional wireless sensor networks' power is supplied by battery that has finite energy storage.Once the battery is exhausted,it will limit the operation time of WSNs.Although it can prolong the lifetime of energy-constrained wireless networks by battery replaced or recharged,it is too difficult to achieve.Thus energy harvesting technology comes into being to solve the problems of energy supply in WSNs.Compared with traditional energy harvesting technology which is susceptible to the position and climate because it harvests energy from natural environment,such as solar,wind,thermoelectricity and so on,energy harvesting from radio frequency signals has drawn significant attentions.RF signal not only can compensate the defect of the harvesting environment for natural energy,but also has the advantage of carrying information together with energy to provide great possibility for information and energy transferring simultaneously.Simultaneous wireless information and power transfer(SWIPT)technology is the product of wireless information transmission technology and wireless energy harvesting technology that scavenges energy from ambient RF signals to achieve wireless information and energy transmission at the same time.SWIPT technology is a promising solution to achieve efficient and reliable information communication,what's more,it has brought profound changes in wireless communication systems design and wireless resource allocation.The existing works on SWIPT technology are mainly based on three methods: power splitting,time switching and antenna selection,whose receivers need to design a splitter to achieve information and energy receiving simultaneously,which results in complex design and high cost for SWIPT technology.With the background of WSNs,this paper combines Orthogonal Frequency Division Multiplexing(OFDM)technology and cooperative relay technology with SWIPT technology,not only optimizing the efficiency of energy and spectrum in SWIPT transmission,but also making SWIPT technology applied with simple design and low cost in WSNs.The main works and conclusions of this paper are as follows:(1)In the situation of complex design and high cost in the receiver,we propose a SWIPT algorithm based on resource allocation in OFDM systems according to the characteristic of OFDM technology is capable of allocating subcarriers flexibly and controlling the transmission power in every subcarrier.In this algorithm,the sensor transmitter node transmits the information to the receiver node.Then the receiver node with no extra splitter design only needs to allocate a portion of subcarriers for information decoding,and allocate the remaining for energy harvesting in the light of channel condition.We study the joint optimization of subcarrier and power allocation at the receiver node to maximize the harvested energy while achieve the target rate.Simulation results confirm better performance in our proposed algorithm than other existing algorithms.(2)To make further efforts to improve the efficiency of spectrum and energy in SWIPT systems,we propose a SWIPT algorithm based on resource allocation in OFDM cooperative relay systems according to characteristic,that cooperative relay technology is able to maximize the performance of wireless communication networks by means of multi-node relaying.We analyze the allocation optimization problem within two time slots.In the first time slot,sensor source node broadcasts its RF signals for destination node and relay node to receive.Nevertheless,the destination node can't receive the information accurately owing to the bad channel condition so that the relay node receive information while harvesting energy.In the second time slot,the relay node with no sacrifice adopts two cooperative relay modes: decode and forward and amplify and forward to help forward the information to the destination node by utilizing the harvested energy,so that the destination node is capable of receiving the information from the source node accurately.Meanwhile,it promotes the efficiency of energy and spectrum.Simulations results demonstrate the better performance of the proposed algorithm comparing with other algorithms.