Research On Wireless Multicast In Sparse Code Multiple Access Enabled Networks

With the rapid development of mobile internet,the number of devices ac-cess and data traffic will explode,and then the limited spectrum resources are difficult to meet the requirement of the fast-growing mobile services.In the massive connection scenario,the applications for services like live-streaming and video conferencing will become more and more widely.If these data are transmitted by traditional orthogonal multiple access(OMA)and wireless uni-cast,the system resources will be heavily occupied,which will inevitably aggra-vate the shortage of spectrum resources.Sparse code multiple access(SCMA)is a new type of code domain non-orthogonal multiple access technology.It not only improves the number of access users,but also provides spread spectrum gain and coding gain.The broadcast characteristics of the wireless channel is utilized in wireless multicast system.This make the base station can transmit the same data to multiple users with the same time-frequency resource,and then improves the link utilization.The researching of SOMA-based wireless mul-ticast system can make full use of their advantages.It not only improves air interface efficiency,but also save the spectrum resources.This thesis studies SCMA-based wireless multicast technology in terms of performance analysis,system design and resource allocation.The main research contents are listed as follows:(1)Theoretical analysis and verification of the performance of the SCMA multicast system.As a new type of multiple access technology,the perfor-mance of multicast systems in SCMA networks has not been fully analyzed and explored.We derive the closed expression for the average outage probabil-ity of the users,and verify the gain of the SCMA multicast system by comparing with the traditional OMA multicast system both in theoretical analysis and nu-merical simulation.Considering the characteristics of code domain multiple access of the SCMA system,the BER(Bit Error Ratio)performance of SCMA multicast system is studied.Firstly,an upper boundary of BER of SCMA uni-cast system is analyzed.Based on the upper boundary and the characteristics of the wireless multicast system,we derive the closed expression of the BER upper boundary for SCMA multicast system.Considering the complexity of the obtained expression,it is difficult to directly analyze the effects of the key parameters on system performance.Therefore,we derive a progressive expres-sion of the upper boundary when the number of users tends to infinity,and then obtain the impact of signal to noise ratio(SNR)and the number of users on the system performance.(2)To solve the problem that the multicast rate is limited by the worst users in the group,we study the layered multicast in SCMA networks.We in-troduce the layerd source coding into the SCMA multicast system and propose two transmission schemes based on the availability of channel status informa-tion(CSI).The first transmission scheme requires each user to feed back CSI to the base station.Although a lot of feedback overhead is generated,it is possible to ensure that all users have the most basic quality of service.The second trans-mission scheme does not require the CSI of each user,but the basic quality of service for all users is not be guaranteed.Since the former needs to dynamically adj ust the transmission strategy according to CSI,we propose a suboptimal fast algorithm for this scheme.For the second transmission scheme,we propose an optimal resource allocation algorithm.The simulation results show that the out-age performance and system capacity for the layered multicast are better than those for the traditional multicast.The proposed resource allocation algorithms can effectively improve system performance.(3)To utilize the cooperative diversity gain to improve the communica-tion reliability,we study the cooperative multicast system in SCMA network.We propose a relay cooperative multicast system model for SCMA network.Based on the proposed model,we firstly derive the exact expression of the av-erage outage probability of the users using mathematical theory.Secondly,the asymptotic expression of the outage probability in the high SNR scenario is analyzed,and the optimal power allocation and relay position are solved by theoretical analysis and numerical strategy.Finally,the correctness of the ex-act expression and the effectiveness of the proposed scheme are verified by the simulation results.Compared with direct multicast systems,SCMA coopera-tive multicast can effectively reduce the average outage probability of users.The proposed relay design scheme can further improve system performance.The cooperative multicast has higher available rate and lower transmission de-lay than the direct multicast under the constraint of outage probability.