Noma-based Wireless Multicast Transmission Technology For 5G

Wireless multicast transmission technology has highly improved spectrum efficiency of communication systems.However,facing the contradiction be-tween the increasment of requests for multicast services caused by sultra-large-scale access demand in 5G and the reduction of avaliable spectrum for multicast services,the existing OFDMA-based multicast transmission schemes are.no longer able to cope with,because they only allow one MG(Multicast Group,MG)or some of users in MG to be served by the same one time-frequency resource.Since NOMA technology has extended the wireless resource from time-frequency domain to power domain,this thesis introduces NOMA into multicast transmis-sion.New NOMA-based transmission schemes are proposed,and correspond-ing strategy is given for existing problem.It provides a theoretical basis for the study of serving users in two MGs on the same time-frequency resource.The main contributions of this thesis include the following three aspects:(1)In order to transmit two MGs’ required signals on the same time-frequency resource,this thesis proposes NOMA-based joint transmission scheme for two MGs(termed as MS-NOMA)to extend the condition of unicast user pair formation in NOMA technology to that of multicast subgroup pair formation.On the basis of summarizing the relationship between the intervals of two MGs’channel gains,maximum and minimum group strategy is given to achieve strict difference in channel gain between MGs.Subgroups with strict channel gain difference from each other and belonging to different MGs are paired.Accord-ing to different subgroup pairs,three transmission modes that can serve all users in two MGs are researched.Under these transmission modes,the spectral ef-ficiency analysis method is given.MS-NOMA scheme uses the transmission mode with maximum spectrum efficiency to delivery data.Simulation results show that on the premise of occupying the same bandwidth as the OFDMA-based multicast transmission technology,through MS-NOMA,average service ratio and system spectrum efficiency are enhanced.(2)In MS-NOMA,the adoptation of successive interference cancellation technology causes signal wastage.Conventional cooperative multicast scheme that only realizes cooperation within a single MG has the problem of limited cooperation.To jointly solve above two problems,NOMA-bsed cooperative opportunistic multicast transmission scheme for two MGs(termed as COM-NOMA)is proposed.It extends inter-group cooperation to intra-group cooper-ation.In the existing researches,each required signal is forwarding signal dur-ing cooperation process.Inter-group isolation is produced.In order to avoid this,NOMA signal that superimposes both two required signals is utilized in COM-NOMA.Firstly,base station multicasts NOMA signal to two MG by MS-NOMA,and makes a fixed proportion of users with good channel conditions to successfully receive.Thus,the joint opportunistic multicast is accomplished.Successfully receiving user as UR(User Relay,UR)forwards NOMA signal to unsuccessfully receiving user.And the cooperation between two MGs is real-ized under the same NOMA signal requirement.By analyzing the successful reception condition of NOMA signal in joint opportunistic multicast,the SINR threshold that UR should provide for unsuccessfully receiving user is given.Moreover,the approximate expression of system coverage ratio is derived.To reduce the complexity of the integral calculation,annular sector approxima-tion is used.Simulation results show that spectrum efficiency per unit energy consumption is raised via COM-NOMA,and analytical results of the system coverage ratio match well with simulated ones.(3)In cooperative multicast transmission scheme,successfully receiving users are unevenly distributed due to path loss.All unsuccessfully receiving users select UR within the efficient transmission range of device,which is the maximum of ERSR(Efficient Relay Selection Range,ERSR),or even within overall cellular.Under high-density connections,this leads to UR redundancy and low coverage efficiency.To tackle these problems,based on the optional ERSR radius in D2D device discovery mechanism,RDUR(Range-division User Relay,RDUR)selection strategy is proposed.The selectable radius of ERSR is flexibly assigned to unsuccessfully receiving users in each AA annu-lar area,which has different distance from base station.And then,the ERSR radius set of annular areas is determined with the goal of maximizing UR cover-age efficiency.The Poisson distribution characteristic of UR number in ERSR is leveraged to analyze UR selection ratio in scenario of COM-NOMA.And average repetition rate is introduced to eliminate the number of URs selected repeatedly.Its expression under different radius sets is derived.Simulation re-sults show that,with RDUR strategy,UR reduandancy is reduced by about 12%,and spectrum efficiency per unit UR and coverage efficiency are improved.In addidation,analytical results of UR selection ratio match well with simulated ones.Finally,the investigations of the whole thesis are summaried.On this ba-sis,the future research directions of wireless multicast transmission technology are prospected,and several valuable research interests are discussed.