Resource Allocation Of Cooperative NOMA Cognitive Radio Systems

The demand for data rate of the fifth generation(5G)mobile communication networks increases exponentially which requires a large amount of spectrum resource.However,the available spectrum is currently allocated in a fixed manner and the allocated spectrum is not fully utilized.Cognitive radio(CR)technology is a technical solution to solve the problem that spectrum resources are not fully utilized due to fixed static spectrum allocation and meet the increasing demand for wireless applications.Meanwhile,Non-orthogonal Multiple Access(NOMA)technology is one of the most advanced technologies for 5G,which each subchannel can serve multiple users at the same time,with each user being assigned different power.The introduction of NOMA technology to CR technology has also become a possibility to improve the efficiency of spectrum utilization.Orthogonal frequency division multiplexing(OFDM)technology can effectively divide spectrum resources into multiple subcarriers,so that users can use spectrum resources more flexibly.Hence,this thesis investigates combining CR,NOMA and OFDM to improve the spectrum utilization.A NOMA-CR system based on cooperation between users is proposed,where the secondary user(SU)is used as a relay to cooperate with the primary user(PU)and SU can be selected as relays if the PU is not in the base station(BS)service range or the channel state is bad and the SU channel state is good.The NOMA-CR system transmission is divided into two phases.In the first transmission phase,the primary base station(BS)transmits the information of PU and SU to the SU which is allocated as a relay.Then,SU decodes the information of PU user first by Successive Interference Cancellation(SIC),then decodes the information of SU user.In the second transmission phase,SU transmit information of PU through direct transmission.This cooperative NOMA access strategy not only improves the efficiency of spectrum utilization,but also is a win-win strategy to improve the transmission rate of both SU and PU.For the multi-PU multi-SU multi-carrier NOMA cognitive radio systems,it is necessary to dynamically allocate the resources of PU and SU according to the channel conditions of users,so as to maximize the system capacity.Firstly,matching algorithm is used to allocate subcarriers and user pairing between PU and SU.Then Difference of Convex(DC)algorithm is used to allocate the power of PU and SU on each subcarrier to improve the cooperative data rate of PU and SU on each subcarrier,thus improving the efficiency of spectrum resource utilization.Compared with the traditional multi-carrier cognitive relay system,the proposed multi-carrier NOMA cognitive radio system significantly improves spectrum efficiency.