Research On Resource Allocation Algorithms In Energy Harvesting Relay Systems

With the rapid development of mobile communication technology,the requirement of network quality and data rate is higher and higher.The emergence of cooperative relay technology could solve the problem of weak coverage of cell edge effectively,and can provide a good diversity gain to certain extent.As an advanced technology in recent years,energy harvesting could achieve the goal of green communication by collecting energy from renewable resources in the surrounding environment.Therefore,the combination of cooperative relay and energy harvesting is a hot research topic currently.In this thesis,the system performance and the resource allocation algorithms of the system with energy harvesting relays are studied.Taking a multi relays system into consideration,a closed-form outage probability expression is derived and the resource allocation problems are analyzed.Also the modulation method is studied in this thesis and both offline and online schemes are studied to improve the system performance.To sum up,the main contents are as follows:(1)A closed-form outage probability expression is derived for the cooperative relaying system using energy harvesting.Consider a wireless system with multiple energy harvesting relays and all the relays are assumed to be energy harvested nodes with simultaneous wireless and information transfer(SWIPT)capabilities,which means the relays are wirelessly powered by harvesting energy from the received signal.Based on the characteristic function of the system's probability density function(PDF)with only one relay,we derive the close-form outage probability expression using the fitting algorithm to simplify the complex part in the characteristic function.The simulation result shows that the derived expression of the outage probability is accuracy and gives insights into the effect of various system parameters on the performance of protocols.(2)Based on the close-form expression,an optimization problem is built to minimize the outage probability under different constraints.Considering the complexity of the outage probability expression,an approximation method is given to simplify the expression.Under different transmit power constrains,an optimization problem is built to minimize the outage probability under different constraints.The Lagrange method and Karush–Kuhn–Tucker(KKT)condition is used to solve the optimization problems to jointly optimize relay's power split factors and the transmit power.The simulation result shows that the proposed optimization algorithms can offer superior performance and the improvement is the same for different system conditions.(3)An offline transmission scheme is proposed for the nodes to adaptively adjust the modulation method in an energy harvesting relay system.Both the source node and the relay node adjust M-ary quadrature amplitude modulation(MQAM)level and choose the corresponding transmitted power.Based on the data buffer state,the QAM level for the source node is determined.Following this,the relay node adaptively choose its QAM level based on whole view of the system information including channel state information and energy storage information with the help of reinforcing learning method.The simulation result shows that the offline scheme improves the total system throughput.(4)Two online transmission schemes are proposed for the relay node to adaptively adjust the modulation method in the similar energy harvesting relay system.The assumption is made that the relay node only has the causal system information.Taking the result of the offline scheme as training data,two different classification methods are analyzed according to the channel state information and the energy buffer information.With the class,the relay node can determine the modulation level of MQAM modulation method in order to improve total system throughput.The simulation result shows that the online scheme also improves the system performance.