Research On Cooperative Access Mechanism Based On Wireless Energy Harvesting In Ultra Dense Network

The wireless communication has a mushroom growth over the years.Meanwhile,the emerging applications such as virtual reality and interactive games continue to appear,which puts forward increasing requirements of uplink(UL)data transmission and communication reliability.The researchers deploy abundant access points(APs)with low power in hot spot,and ultra dense network(UDN)is built to support high data rate and massive connections via shortening the distance between AP and user and reducing the path loss.However,the plentiful terminals and APs result in high energy consumption in UDN.In order to realize the sustainable development of green communication and prolong the battery lifetime,energy harvesting(EH)technology is introduced into UDN.In EH-based UDN,the serious interference and resource shortage among users are caused,owing to the limited wireless resources and the densely deployed nodes.APs grouping in EH-based UDN acts as an efficient scheme.APs grouping means that multiple APs may cooperate as a group to provide the access service for a user,and a user can access to several APs and allocate resources effectively to reduce interference,improve spectrum efficiency and optimize network throughput.Nowadays,researchers have conducted extensive research on APs grouping and user collaboration in EH-based UDN.However,the selection of APs,the way of user collaboration and the optimization of energy and communication resources in EH-based UDN requires further study.Therefore,this thesis studies the above problem and the main work is as follows:This thesis proposes a novel APs grouping and resource allocation scheme to maximize the throughput via jointly optimizing energy and time allocation of downlink(DL)and UL in EH-based UDN.In order to ensure that the user's energy harvested from APs is sufficient to transmit data,a probability function is presented with the energy relationship of DL and UL to jointly optimize the EH range and the time allocation.Moreover,the APs are divided into groups based on the EH range obtained by the function.And the user harvests energy during DL and transmits data during UL.To derive the optimal solution of the formulated power allocation problem for the selected APs,this thesis adopts particle swarm optimization(PSO)algorithm.The performance of the proposed scheme is verified.And that has higher throughput compared with existing APs grouping schemes.When energy AP(E-AP)and data APs(D-APs)locate separately in multiple APs and multiple users' scenario,this thesis proposes a user collaboration scheme jointly considering time and power allocation in EH-based UDN to solve the problem of doubly near-far effect.Doubly near-far effect refers to that edge user has lower energy collection efficiency and lower data transmission rate,while near user harvests more energy under the same circumstances,resulting in energy waste.Particularly,the users are divided into collaborative users and independent users under the constraint of each user's UL data rate.This thesis applies energy and distance-based one-to-one matching algorithm to divide collaborative users into energy relay and data relay.In order to ensure the edge user's data rate,the user collaboration is adopted.The user near E-AP acts as energy relay and helps the user near D-AP to harvest enough energy during DL,and in return,this user acts as data relay to transmit its energy relay's data during UL cooperatively.The overall throughput is maximized via federatively optimizing the time and the power resources allocation between user collaboration and transmission between users and APs under the constraint of each user's transmission power and UL data rate.Simulation results show that the proposed scheme has good throughput performance compared with existing direct transmission algorithm and collaborative transmission algorithm.