Research On The Multicast Function Of MAC Layer In LTE Broadband Trunking System

Broadband trunking system is a professional command and dispatch communication system which can provide broadband communication services,mainly used in transportation communication,government communication,logistics communication,public security and other departments.The function of multimedia trunking communication in long term evolution(LTE)broadband trunking system is implemented by utilizing orthogonal frequency division multiplexing,multiple input multiple output and hybrid automsatic retransmission technique in LTE.The function of point-to-multipoint data transmission in MAC layer is realized by using multicast technologies such as channel mapping and MBMS service scheduling.Therefore,the research on the multicast function of MAC layer in LTE broadband trunking system is of great practical value.Based on the previous contributions of broadband tranking systems at home and abroad,the multicast flinction of MAC layer in LTE broadband trunking system is researched and realized,the main contributions are listed as follows:1.Based on the architecture of MBMS,the control plane protocol stack of MBMS and the user plane protocol stack of MBMS in LTE broadband trunking system,the transmission mode of MBMS is analyzed,the architecture and functions of MAC layer in LTE broadband trunking system are proposed.2.By researching on the channel mapping technology of MAC layer,MBMS resource scheduling mechanism,synchronization processing mechanism of MBMS control signaling and synchronization processing mechanism of MBMS service data,the MBMS resource scheduling process of MAC layer,MBMS session opening process,MBMS session stopping process and MBMS session update process are designed.3.An IMMA algorithm,which considers the tradeoff of spectral efficiency and fairness,is proposed.Based on the traditional multicast resource scheduling algorithms MIN and MAX,the channel condition of users,the average packet loss rate of users and the fairness between users in MBMS group are synthetically optimized in IMMA algorithm.The data rate of the MBMS multicast group is selected by combining the link adaptation and the average packet loss rate of users.The system throughput and overall fairness are further equalized.Analytical resukts and simulation results show that the IMMA algorithm is capable of outperforming on system throughput and fairness of users by comparing with MIN and MAX algorithms.4.A software architecture of MAC layer in LTE broadband trunking system is proposed.The architecture combines the multicast function of MAC layer,which is highly scalable,interoperable and easy to test.Based on the Linux operating system,the multiplexing demultiplexing module,the scheduling module,the MAC control module,the packet loss processing module,the interface between MAC layer and PHY layer,the interface between MAC layer and RLC layer,the interface between MAC layer and RRC layer,the MCE entity and the user plane interface M1 between the base station and the broadcast multicast service gateway are developed by using C language.The multicast function of MAC layer is implemented.5.The verification platform of the MAC layer multicast function for LTE broadband trunking system is established.The functions such as the MBMS session start,the MBMS session stop,the MBMS session update,the mapping between transport channels and logical channels,the generation of MCH MAC PDU,the scheduling SIB 13 of MAC layer,the scheduling MBMS control information and MBMS service data of MAC layer are verified.The performances such as the relationship between downlink BLER and SNR in MAC layer and the throughput of users under different modulation and coding modes are verified.The verification results show that the multicast function implemented by MAC layer satisfies the design requirements of the LTE broadband trunking system.