Joint Resource Optimization For Cognitive Sensor Networks Based On Energy-harvesting Relay

As an energy-constrained wireless networks,wireless sensor networks(WSNs)are usually powered by fixed energy supplies(e.g.,batteries),which limits the operation time of networks.Simultaneous wireless information and power transfer(SWIPT)is a promising technology for prolonging the lifetime of energy-constrained networks,which makes full use of the radio-frequency(RF)signal that can carry information and energy simultaneously.The unlicensed bands where sensor nodes work is increasingly crowded,which would influence the communication performance of the WSNs.As a feasible technology that aims to solve the problem of spectrum scarcity,cognitive radio(CR)allows secondary users access to the licensed bands on the condition that do not significantly affect the communication performance of primary users.Hence,WSNs can utilize CR technology to solve the problem of crowded bands.Under the background of cognitive sensor networks(CSNs)based on energy-harvesting(EH)relay,this paper combines orthogonal frequency division multiplexing(OFDM)technology to further improve the communication performance of the networks.The main work and achievements of this paper including as follows:(1)To solve the problem that not fully consider the interference that caused by primary users to secondary users and the optimal power splitting ratio can only be obtained by exhaustive search in recent research,we first propose an EH amplify-and-forward(AF)relaying spectrum access strategy based on joint optimization of power.In this method,the cognitive network should guarantee the interference caused by secondary users to primary users is within the permissible threshold in order to access the licensed spectrum.Moreover,in cognitive network,the signal transmitted from source node to destination node is forwarded by EH relay node,the EH relay node utilize power splitting(PS)receiver architecture to harvest energy and receive information.Simultaneously,in this method,we proposes a joint resource optimization algorithm to obtain the closed-form solution of transmission power and power splitting ratio,which aims at maximize the achievable rate of cognitive users.Simulation result demonstrates that there is no performance gap between our proposed algorithm and the exhaustive search method.In order to improve the communication performance of network,we propose another EH decode-and-forward(DF)relaying spectrum access strategy based on joint optimization of power,in the simulation result,we demonstrate that DF relaying protocol is better than AF relaying protocol at performance by comparing with first method.(2)To avoid the interference between primary users and secondary users in the last part content,we combine the OFDM technology and propose two EH relaying spectrum access strategy based on joint optimization of subcarrier,as an EH relay,secondary user utilizes the left subcarriers to transmit its own signals on the condition that utilizes part of subcarriers to help primary users to achieve the target rate,which would eliminate the interference between primary users and secondary users.We first propose a EH DF relaying spectrum access strategy based on joint optimization of subcarrier,and as an EH relay,secondary user utilizes PS receiver architecture.This method aims at joint optimization of transmission power,power splitting ratio and subcarrier allocation to maximize the achievable rate of secondary users.In order to reduce the difficulty and cost of the implementation of EH receiver,we propose another EH AF relaying spectrum access strategy based on joint optimization of subcarrier,as an EH relay,secondary user utilize a part of subcarriers to accept information and the other part to harvest energy and require no extra splitter design.Simulation result shows that two methods we proposed allow secondary users access licensed band on the condition that guarantee the communication performance of primary users.