Resource Allocation For Cooperative NOMA Systems Based On Energy Harvesting

With the rapid development of wireless communication technology and Internet technology,the number of mobile terminal equipments is growing,and the demands of users for the quality of service(Qo S)and transmission rates of devices are increasing.Therefore,non-orthogonal multiple access(NOMA)technology has attracted increasing attention.Different from the conventional orthogonal multiple access(OMA)technology,NOMA provides services for multiple users in each orthogonal resource block(such as time,frequency),so as to improve the spectrum utilization and access capacity of the system.Cooperative communication uses relays for forwarding to achieve communication between source and destination nodes.Therefore,the combination of NOMA and cooperative communications can be applied to better ensure the Qo S of users at the edge of the system.In addition to improving spectrum utilization,energy efficiency is also one of the concerns in the future of wireless communications.By harvesting energy from the radio-frequency signals,wireless energy harvesting technology can supply energy for mobile devices with limited energy requirements,so as to extend the service life of them.Simultaneous Wireless Information and Power Transfer(SWIPT)is a scheme of wireless energy harvesting technology,and it can transmit energy and signals simultaneously.In this thesis,resource allocation in downlink cooperative multicarrier NOMA system based on wireless energy harvesting is studied.The main contributions of this thesis are:First,a resource allocation scheme in downlink cooperative NOMA system with wireless energy harvesting is proposed.The system model includes a base station,a near user,and a far user.It is assumed that there is no direct link between the base station and the far user.The base station adopts NOMA to transmit the signals of the near and far users to the near user on the same channel.The near user decodes the received signal,and then forwards the signal of the far user to ensure the Qo S of the far user.In order to compensate for the energy loss caused by signal forwarding,SWIPT is applied at the near user to divide the received signal into two parts,one for information decoding and the other for energy harvesting.Under the constraints of the minimum data of the far user,the transmission power of the base station and the energy causality of the near user,the number of data bits received at the near user is maximized by optimizing time allocation,power allocation,subcarrier allocation,etc.The simulation results show that the proposed scheme can effectively improve the transmission performance of the near user compared to the conventional OMA scheme and the NOMA scheme with fixed power allocation coefficient or power splitting ratio.In addition,using near users as relays for cooperative communication can also expand the coverage of base station.Secondly,this thesis considers a system model similar to the one used in the previous scheme,except that an energy harvesting relay is added between the base station and the far user for auxiliary transmission based on the existing near user as the forwarding relay,so as to better guarantee the service quality of the remote user.A relay assisted cooperative NOMA resource allocation scheme based on SWIPT is proposed.In this scheme,the base station uses the relay and the near user to forward signal to the far user simultaneously,and SWIPT technology is used by both the relay and the near user to ensure power supply for forwarding.The purpose of this scheme is to maximize the number of data bits received at the near user on the premise of guaranteeing the Qo S of the far users by optimizing the resource allocation in the system.The block-coordinate descent method is used to solve this problem by iteratively optimizing some variables with the other variables fixed.The problem is first transformed into multiple convex optimization problems and linear problems,and then the Lagrange duality method and the bisection search method are applied to solve them.The simulation results show that,compared with the conventional OMA scheme,the cooperative NOMA scheme without relay assistance,and the non-cooperative NOMA scheme with relay assistance,the proposed cooperative NOMA scheme with relay assistance has strong superiority both in terms of near-user transmission performance and far-user service quality assurance.