Resource Allocation In Multi-Cell Wireless Powered Communication Networks

With the ever-accelerating progress of information and communications technology,increasing wireless devices are being connected to the Internet and it gives rise to “Internet-of-Things(IoT)”.However,IoT devices face a tremendous challenge in energy limitation and battery lifetime due to the size and space constraints.To this end,radio-frequency(RF)energy harvesting technology utilizes the radiated characteristics of electromagnetic waves to provide stable and continuous energy for wireless devices in communication networks.Nowadays,RF energy harvesting has attracted considerable attention from researchers,one typical direction of which is wireless powered communication network(WPCN).However,most researches focus on a single-cell WPCN.In real life,the multi-cell WPCNs are more practical and can accommodate the increasing number of network devices.Therefore,this thesis mainly studies the multi-cell WPCN and resource optimization.This paper first introduces the topic background,the related concepts and application scenarios of WPCN.Then the two proposed multi-cell WPCN models are investigated,which are the multi-cell WPCN with load-coupling and the multi-cell WPCN with non-orthogonal multiple access(NOMA),respectively.Moreover,we achieve the resource optimization and analyse the system performance.The detailed research works of this paper are summarized as follows:1)This paper focuses on the time allocation for the max-min fairness throughput optimization and max-sum throughput optimization in a multi-cell WPCN.Since interference of multi-cell WPCN is difficult to be calculated,we consider the multi-cell WPCN with load-coupling and the long-term average interference at all hybrid access points(HAPs).However,the max-min fairness throughput and max-sum throughput optimization problems are nonconvex.To deal with this challenge,two optimization approaches are proposed to transform them into convex ones by variable introduction and mathematical transformation,which enables us to utilize mature algorithms to solve them with global optimality.Simulation results demonstrate the effectiveness of the two proposed approaches.2)This paper investigates the joint time and power allocation for the max-min fairness throughput optimization and max-sum throughput optimization in a multi-cell WPCN with NOMA.However,both of two optimization problems are nonconvex due to the complicated cochannel interference and the coupled time and power variables.To deal with this challenge,efficient two-stage approaches are proposed to transform them into more tractable ones.Specifically,for the max-min fairness throughput optimization problem,we first convert the power allocation problem into a geometric programming(GP)problem for given time allocation and then optimize the time allocation.For the max-sum throughput optimization problem,we first transform the power allocation problem into a signomial programming(SP)problem with fixed time allocation,which is further approximated as a GP one.Then the time allocation is optimized.Simulation results validate the effectiveness of the two proposed approaches.