Resource Allocation For NOMA-based Hybrid Duplex Relay Systems

After years of development,mobile communication technology has grown from 1G to 4G,and is about to enter the 5G era.In the traditional multiple access schemes,different users avoid inter-user interference by allocating orthogonal resources(time,frequency,or codes).With the rapid development of mobile Internet technology and Internet of Things technology,the data throughput in wireless networks will increase by a thousand times compared to now,which requires 5G communication systems to have higher spectrum efficiency and allow more device to access.In this case,the traditional orthogonal multiple access scheme can not meet the communication requirements,and the non-orthogonal multiple access(NOMA)technology is called a very promising solution because it can utilize the power domain.The Non-orthogonality in power domain provides more user access and improves spectrum efficiency.Relay technology has been widely used in mobile communicatio n systems because of its low deployment cost and relativel y simple communication protocol.It can expand the coverage of wireless communication systems and effectively improve the data throughput of cell edge users.In the future dense cellular network system,the base station will be miniaturized,so its coverage is limited,while the number of access devices may be large,and the quality of service of some cell edge users may be poor.In this case,the relay is utilized to improve the quality of service of those users.The NOMA technology can improve the spectrum efficiency,increase the device access and relay can expand the communication coverage,so this paper mainly studies the resource allocation problem in a NOMA-based hybrid duplex system.In the proposed system,the relay can dynamically switches its work mode between full-duplex mode or half-duplex mode,which is decided by a mode selection algorithm based on the condition of the self-interference channel;and a weighted DC algorithm is proposed to solve the power allocation problem under the NOMA scheme.At the same time,the transmission durations for the consecutive slots are asymmetric,which maximizes the throughput of the system.The simulation results show that when working in half-duplex mode,the proposed system has greater data throughput than traditional half-duplex NOMA-based relay systems,due to its asymmetric transmission time allocation scheme.In the hybrid-duplex mode,the system can dynamically select the duplex mode to get better performance by its channel state information,thereby improving the overall communication capability of the system.