Research On The Application Of Co-frequency Co-time Full-Duplex In MAC Layer Of 5G Communication System

With the successful deployment and popularity of 4G,researchers and industry have turned their attention to 5G technology.The upcoming era of Internet of Things and Artificial Intelligence will result in an explosive growth in the number of data and wireless terminals that can access the network.However,the spectrum resources that can be used for short-range wireless communication are extremely limited.In the face of the unlimited growth of demand for wireless services,wireless spectrum resources are becoming increasingly scarce.There is an urgent need to use technologies that can efficiently use spectrum resources in next-generation 5G or even future wireless communication systems,to ease the current wireless spectrum pressure.Although Frequency Division Duplex(FDD)and Time Division Duplex(TDD)are widely used in 4G mobile wireless networks,both FDD and TDD are based on Half Duplex(HD)transmission mode,so they have the inherent drawback of low spectral efficiency.As one of the potential key technologies in 5G,Co-frequency Co-time Full Duplex(CCFD)technology can simultaneously establish two data links in the same frequency band and in the same time slot,which can theoretically increase the spectrum utilization by several times,and effectively reduce the end-to-end delay.As the self-interference cancellation technology continues to mature,CCFD technology can allow a single node to send and receive data in the same frequency band and in the same time slot.However,in order to carry out effective and orderly cooperative communication among multiple nodes and to exert the advantages of CCFD,Media Access Control(MAC)layer is required for further management and scheduling.This paper combines CCFD duplex characteristic to design relevant MAC layer protocol in the centralized wireless communication system that consists of multiple nodes,and do performance analysis and verification.The main research contents and innovations are as follows:First,the FD-MAC(Full-Duplex Media Access Control)protocol applicable to a centralized wireless network is proposed.This protocol is based on the RTS/CTS mechanism of CSMA/CA.It adds two new control frames and improves thecommunication process.It provides symmetrical and asymmetric bidirectional full-duplex mode communication through flexible combination of control frames,and is compatible with unidirectional uplink and downlink HD mode communication.In addition,for the problem of control frame collision when accessing a channel,a Collision Conversion Strategy is proposed.A partial collision condition is converted into a feasible communication mode to ensure normal data communication by using the combination relationship between control frames.Second,combining the communication characteristics of CCFD,the full-duplex setup probability q is introduced in the Markov model of HD wireless network,then a Markov model applicable to centralized CCFD wireless network is proposed.Use this model to deduce and analyze the throughput and delay performance of the proposed FD-MAC protocol.Third,for the inter-node interference(INI)problem in asymmetric bidirectional full-duplex communication mode,the FD-MAC protocol proposed in this paper is improved by selecting a suitable downlink receiving node and using a distributed Power-Control mechanism,which effectively inhibit the INI problem.Not only consider the INI problem when the uplink and downlink simultaneously send data frames,but also consider the INI problem when the uplink and downlink have received the data frame and return the ACK frame at the same time.The performance of the proposed FD-MAC protocol is verified by simulation.The results show that the FD-MAC protocol can improve the throughput performance of the system,and the obtained channel saturation throughput is nearly twice that of the HD mode communication,improving the efficiency of spectrum utilization and achieving lower end-to-end delay.In addition,CCFD mode communication facilitates downlink data transmission,and the base station node can obtain low system delay.The CCFD technology is more suitable for a centralized wireless network with a large amount of downlink data and symmetrical uplink and downlink data flows.