基于LTE-A Pro的传输时间间隔（TTI）的优化研究

发布时间：2018-06-09 11:07

本文选题：传输时间间隔 + 子帧长度　；参考：《北京交通大学》2017年硕士论文

【摘要】：更高的数据速率,更低的数据延迟一直都是无线通信系统演进的目标,也是第四代移动通信技术(4th Generation,4G)相对于上一代移动无线通信技术的显著优势。而与4G相比,第五代移动通信技术(5th Generation,5G)更是明确提出了要进一步增大用户数据峰值速率、减小空中接口时延。作为4G和5G之间的过渡阶段,长期演进技术升级版后续(Long Term Evolution-Advanced Pro,LTE-APro)的目标之一就是在4G的基础上进一步减小用户时延,增大系统吞吐量,为5G的到来做好铺垫。考虑到缩减用户时延可以提高无线资源的利用效率,提高控制信令的传输速度,减小呼叫设置或承载设置时间,而传输时间间隔(Transmission Time Interval,TTI)是用户传输时延的重要组成部分,本文提出了通过优化TTI来减小用户传输时延的方法。虽然第三代合作伙伴计划(3rd Generation Partnership Project,3GPP)提出的各种预调度策略可以减小一部分时延,但是不能很好地兼顾效率问题,本文提出的通过优化TTI减小用户传输时延的方法就不存在效率问题,因此,本文的研究工作非常有必要。为了优化TTI,降低系统传输时延、提高系统吞吐量,本文主要做了两阶段的工作。第一阶段,在长期演进(Long Term Evolution,LTE)系统中,TTI在时间长度上对应着一个子帧的长度,因此可以通过优化子帧结构的方法来优化TTI。在对物理层信道和信号做出适应性改进,保证后向兼容性的前提下,将LTE下行链路子帧长度从14个正交频分复用技术(Orthogonal Frequency Division Multiplexing,OFDM)符号分别缩减为7个OFDM符号和2个OFDM符号。并在静态控制开销的前提下,通过设置最大调度用户数目以及数据包大小等条件,进行了仿真分析,可得在信道条件良好时,子帧长度越短,即TTI越小,系统时延改善越明显。第二阶段的工作在动态控制开销的前提下展开,分为两部分。第一部分,通过设置数据包大小、慢启动阈值等条件,进行了仿真分析。在信道条件良好时,TTI越小,系统性能增益越大。但是由于TTI越小,对硬件的要求越高,对规范协议的改动越大,实现难度也越大。在第二部分工作中,为了兼顾系统性能与实现难度,即在子帧长度为7个OFDM符号的情况下实现最大的系统增益,本文又提出了优化上行链路接入时延和混合自动重传请求(Hybrid Automatic Repeat Request,HARQ)肯定应答/否定应答(Acknowledgement/Non-acknowledgement,ACK/NACK)往返时延的方法。仿真证明,在采用此种方法后,子帧长度为7个OFDM符号时,以传统TII的系统性能作为参考量,对于系统低负载情况下的小区边缘用户和中心用户,系统时延可以减少45.6%和40.6%,优于没有采用此方法的子帧长度为2个OFDM符号的系统性能表现,兼顾了系统性能增益与实现难度。
[Abstract]:Higher data rates and lower data delays have been the goal of the evolution of the wireless communication system and the significant advantage of the fourth generation 4th Generation (4G) relative to the previous generation of mobile wireless communication technology. Compared with the 4G, the fifth generation mobile communication technology (5th Generation, 5G) is more clearly proposed to increase. User data peak rate, reducing air interface delay. As a transition phase between 4G and 5G, one of the goals of Long Term Evolution-Advanced Pro, LTE-APro is to further reduce user delay on the basis of 4G, increase system throughput, paving for the arrival of 5G. Considering the reduction of users Time delay can improve the utilization efficiency of wireless resources, improve the transmission speed of the control signaling, reduce the call setting or load setting time, and the Transmission Time Interval (TTI) is an important part of the user's transmission delay. This paper proposes a method to reduce the transmission delay of the user through the optimization of TTI. Although the third generation of the method is used to reduce the time delay of the user. The various pre scheduling strategies proposed by 3rd Generation Partnership Project (3GPP) can reduce a part of the time delay, but can not give consideration to the efficiency problem well. The method proposed in this paper does not exist the efficiency problem by optimizing the method of reducing the transmission delay of the user by TTI. Therefore, the research work of this paper is very necessary. In order to reduce the TTI transmission delay and improve the system throughput, this paper mainly does two stages of work. In the first stage, in the Long Term Evolution (LTE) system, TTI corresponds to the length of a subframe in the length of time. Therefore, the method of optimizing the subframe structure to optimize the TTI. in the physical layer channel and signal can be optimized. On the premise of adaptive improvement and ensuring backward compatibility, the LTE downlink subframe length is reduced from 14 orthogonal frequency division multiplexing (Orthogonal Frequency Division Multiplexing, OFDM) symbols to 7 OFDM symbols and 2 OFDM symbols respectively. Under the premise of static control overhead, the number and number of the maximum scheduling users are set by setting the number and number of the maximum scheduling. According to the package size and other conditions, the simulation analysis is carried out. When the channel condition is good, the shorter the sub frame length is, the smaller the TTI is, the more obvious the improvement of the system delay. The second stage is divided into two parts under the premise of dynamic control overhead. The first part, the simulation analysis is carried out by setting the packet size, the slow start threshold and so on. When the channel conditions are good, the smaller the TTI, the greater the system performance gain. But the smaller the TTI, the higher the requirement for the hardware, the greater the change to the specification protocol, the greater the difficulty. In the second part, the maximum system increase is achieved in order to give consideration to the system performance and the realization of the difficulty, that is, in the case of the subframe length of 7 OFDM symbols. This paper also proposes a method to optimize the uplink access delay and the Hybrid Automatic Repeat Request (HARQ) affirmative response / negative response (Acknowledgement/Non-acknowledgement, ACK/NACK) round-trip delay. The simulation proves that, when this method is adopted, the length of the subframe is 7 OFDM symbols, and the system is based on the traditional TII. As a reference, the system delay can be reduced by 45.6% and 40.6% for small cell edge users and central users under low load conditions. It is superior to the system performance performance of 2 OFDM symbols without using the subframe length of this method, which takes into account the performance gain and difficulty of the system.
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN929.5

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