SCMA系统中的关键传输技术研究

发布时间：2018-04-28 17:35

本文选题：5G + 稀疏码分多址接入　；参考：《电子科技大学》2017年硕士论文

【摘要】：近年来,移动智能终端的普及、移动互联网、新业务的蓬勃发展促使移动通信系统需要提供满足用户需求的服务。现有的通信系统已不能满足海量用户低延迟、高速率的通信需求,因此稀疏码分多址接入(Sparse Code Multiple Access,SCMA)被提出。它使海量用户以过载的方式复用频谱资源,同时SCMA用户可以采用Grant-free机制降低通信延迟,因此SCMA成为一项第五代移动通信系统(The 5th Generation,5G)中具有巨大应用前景的多用户多址方式。现有关于SCMA的研究主要集中在码本设计、低复杂度接收机设计上,而关于它的传输技术研究相对较少。通信系统的传输技术如能效优化设计、混合自动重传请求(Hybrid Automatic Repeat Request,HARQ)技术影响系统的吞吐量、能效、接收可靠性等,因此研究系统的传输技术具有重要意义。鉴于SCMA对未来通信网络的重要研究意义及SCMA传输技术研究的不足,本文主要对SCMA系统的能效优化设计、HARQ技术进行研究。首先,本文对SCMA系统的能效优化设计进行了研究。提出了两种能效优化模型,第一个优化问题的目标函数为系统所有用户的能效和最优,第二个优化问题的目标函数为使系统最差链路的用户能效最优,两个能效优化问题均保证了SCMA用户的最小传输速率要求。根据所提的两个能效优化问题,设计了两种算法,其基本思想为参量优化迭代。首先引入参量,将分数目标函数形式转为含有参量的凹函数,用库恩塔克条件(Karush-Kuhn-Tucker,KKT)求解得到能效最优的用户功率分配方案后,更新参量,继续求解优化问题,直至优化解满足收敛条件。仿真结果表明,设计的两种能效优化算法分别解决了给定模型下的能效优化问题,具有较好的收敛性。此外,对比两种能效优化算法,可知能效最优不能保证传输速率最优。随后,本文对SCMA系统的可靠性提升进行了研究。根据传统消息传递算法(Message Passing Algorithms,MPA)检测器的译码特点,提出了一种部分码字信息已知的MPA译码器(Part Information based MPA,PI-MPA),定性分析了它相比传统MPA提高译码准确性的原理。基于PI-MPA构造了一种高可靠性的SCMA-HARQ系统,通过分析正确重传码字数目对系统吞吐量和重传延迟的影响,本文设计了一种基于用户QoS分组的部分正确码字动态重传算法机制。将所有用户分为两组,只从QoS较低的那组选择可利用冗余重传用户进行重传,且执行冗余重传的用户数目根据当前传输错误的用户数目自适应确定。仿真结果表明,本文提出的基于PI-MPA的高可靠SCMA-HARQ系统相比传统的SCMA-HARQ系统具有很小的重传延迟性能损失,但可靠性和吞吐性能明显增强。
[Abstract]:In recent years, with the popularity of mobile intelligent terminals, the rapid development of mobile Internet and new services, mobile communication systems need to provide services to meet the needs of users. The existing communication systems can no longer meet the low delay and high speed communication requirements of mass users, so sparse CDMA access (parse Code Multiple access) is proposed. It enables mass users to reuse spectrum resources in an overload manner, and SCMA users can use Grant-free mechanism to reduce communication delay. Therefore, SCMA has become a multiuser multiple access mode with great application prospects in the 5th Generation 5G (the fifth generation mobile communication system). The current research on SCMA is mainly focused on codebook design, low complexity receiver design, but less research on its transmission technology. The transmission technology of communication system, such as energy efficiency optimization design, hybrid automatic retransmission request hybrid Automatic Repeat request HARQ technology, affects the throughput, energy efficiency and receiving reliability of the system, so it is of great significance to study the transmission technology of the system. In view of the importance of SCMA to the future communication network and the shortage of SCMA transmission technology, this paper mainly studies the energy efficiency optimization design of SCMA system and HARQ technology. Firstly, the energy efficiency optimization design of SCMA system is studied. Two energy efficiency optimization models are proposed. The objective function of the first optimization problem is the energy efficiency and optimization of all users of the system, and the objective function of the second optimization problem is to optimize the energy efficiency of the users of the worst link of the system. The two energy efficiency optimization problems ensure the minimum transmission rate requirement of SCMA users. According to the two energy efficiency optimization problems proposed, two algorithms are designed, whose basic idea is parametric optimization iteration. First, the parameter is introduced, the form of fractional objective function is transformed into a concave function with parameters, and the Karush-Kuhn-Tuckern KKT condition is used to solve the optimal user power allocation scheme for energy efficiency, then the parameters are updated and the optimization problem is solved. Until the optimal solution satisfies the convergence condition. The simulation results show that the proposed two energy efficiency optimization algorithms can solve the energy efficiency optimization problem under a given model and have good convergence. In addition, compared with the two energy efficiency optimization algorithms, the energy efficiency optimization can not guarantee the optimal transmission rate. Then, this paper studies the reliability enhancement of SCMA system. According to the decoding characteristics of the traditional message Passing algorithm (MPA) detector, a part Information based MPA-PI-MPAA decoder with known part of codeword information is proposed. The principle of improving the decoding accuracy compared with the traditional MPA is analyzed qualitatively. A high reliability SCMA-HARQ system is constructed based on PI-MPA. By analyzing the influence of the number of correct retransmitted codewords on system throughput and retransmission delay, a partial correct codeword dynamic retransmission algorithm based on user QoS packet is designed in this paper. All users are divided into two groups, and the number of users performing redundant retransmission can be determined adaptively according to the number of users whose current transmission error is based on the number of users who can use redundant retransmission users only from the group with lower QoS. The simulation results show that the proposed high reliability SCMA-HARQ system based on PI-MPA has less performance loss of retransmission delay than the traditional SCMA-HARQ system, but the reliability and throughput performance is obviously enhanced.
【学位授予单位】：电子科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN929.5

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