高铁环境下无线接入技术研究

发布时间：2018-06-05 12:29

本文选题：快时变信道 + 自适应调制编码　；参考：《杭州电子科技大学》2017年硕士论文

【摘要】：高速铁路环境作为高速移动典型的应用场景之一,相对低速情况下需要更稳定可靠的通信系统支撑。高移动性加剧了无线信道时变程度,在如此恶劣的信道环境下,提供稳定可靠的高数据传输速率的用户体验成为一项需要深入研究的课题。本文围绕高速移动环境及高铁场景下,对自适应调制编码(Adaptive Modulation and Coding,AMC)中信道质量指示(Channel Quality Index,CQI)自适应调整算法和频率同步进行研究,具体完成的工作如下:首先,介绍移动通信的发展以及高速铁路专用通信系统演进方向,分析高速移动环境下通信系统面临的问题以及国内外有关高移动环境下的研究热点。其次,介绍无线信道的传播特性和高速环境下的衰落信道,并对高铁环境的信道特点进行阐述以及现有的高铁场景信道模型。此外,介绍几种高速铁路无线接入网络覆盖方案,如单个基带处理单元(Base Band Unite,BBU)+多个射频远端单元RRU(Remote Radio Unite,RRU)的覆盖方式。然后,根据标准中15种调制编码方式以及对应的码率在加性高斯白噪声(Additive White Gaussian Noise,AWGN)信道下仿真获得目标误块率对应的信噪比,建立CQI切换的阈值表,同时引入有效信噪比映射,用单个信噪比值代表多状态信道以降低复杂度。针对CQI固定上报周期的问题,本文提出一种适用于高速移动环境下AMC系统中CQI自适应调整算法和方案,其通过统计帧内相邻符号上的信噪比差值来评估当前信道变化程度,并利用评估结果来预测未来信噪比变化程度。接着基于CQI的量化颗粒度来计算CQI反馈周期自适应调整量,使CQI反馈负载和吞吐量性均能获得相对较好的性能。最后通过计算机仿真验证了本文提出方案的可行性和有效性。最后,在高速移动环境下对频率同步算法性能的影响进行分析。针对多普勒频偏和晶振频偏同时存在的情况下,采用一种正交角域子空间算法,将接收信号投影到各个子空间,并对各子空间内的等效多普勒频偏进行估计,获得多普勒频偏和晶振频偏的混合频偏,然后利用估计的混合频偏对各子空间内的接收信号补偿,达到频率同步的效果。仿真结果表明,未对估计值进行自回归(Autoregressive,AR)滤波能获得较好的误码率性能,这是由于多普勒频偏呈现快速时变,造成滤波无法提高估计值的精度,还增加估计噪声。此外,该算法在大部分采样位置上能够有效降低误比特数,仅在到达角快变情况下特别是在某些特殊场景如到达区域(Arrival Area,AA)和切换区域呈现较高的误比特数。
[Abstract]:As one of the typical application scenarios of high-speed movement, high-speed railway environment needs more stable and reliable communication system support than at low speed. High mobility intensifies the time-varying degree of wireless channel. In such a bad channel environment, providing a stable and reliable user experience with high data transmission rate has become a subject that needs further study. In this paper, the adaptive Modulation and coding algorithm and frequency synchronization of CITIC channel quality indication channel Quality index (CQI) are studied in high speed mobile environment and high-speed railway scene. The detailed work is as follows: first of all, This paper introduces the development of mobile communication and the evolution direction of high-speed railway special communication system, analyzes the problems faced by the communication system in high-speed mobile environment and the research hot spots at home and abroad on the high mobile environment. Secondly, the propagation characteristics of wireless channel and fading channel in high-speed environment are introduced, and the channel characteristics of high-speed rail environment and the existing high-speed rail scene channel model are described. In addition, several high-speed railway wireless access network coverage schemes, such as a single baseband processing unit (Base Band Unite BBU), multiple radio frequency remote units (RRU(Remote Radio Unite RRU), are introduced. Then, according to the 15 modulation coding schemes and the corresponding bit rates in the standard, the SNR corresponding to the target block error rate is obtained by simulation under the additive White Gaussian noise channel, and the threshold table of CQI handoff is established, and the effective signal-to-noise ratio mapping is introduced. The multistate channel is represented by a single signal-to-noise ratio (SNR) value to reduce the complexity. In order to solve the problem of fixed reporting period of CQI, this paper presents an adaptive CQI adjustment algorithm and scheme for AMC systems in high-speed mobile environment, which evaluates the current channel variation by counting the SNR difference between adjacent symbols in the frame. The evaluation results are used to predict the variation of signal-to-noise ratio in the future. Then, based on the quantitative particle size of CQI, the adaptive adjustment of CQI feedback cycle is calculated, so that the feedback load and throughput of CQI can achieve relatively good performance. Finally, the feasibility and effectiveness of the proposed scheme are verified by computer simulation. Finally, the influence of frequency synchronization algorithm in high speed mobile environment is analyzed. In view of the existence of Doppler frequency offset and crystal oscillator frequency offset simultaneously, an orthogonal corner domain subspace algorithm is used to project the received signal to each subspace, and the equivalent Doppler frequency offset in each subspace is estimated. The mixed frequency offset of Doppler frequency offset and crystal oscillator frequency offset is obtained, and the received signals in each subspace are compensated by the estimated mixed frequency offset to achieve the effect of frequency synchronization. The simulation results show that the error rate performance can be obtained without autoregressive ARF filter, which is due to the fast time-varying Doppler frequency offset, which can not improve the estimation accuracy and increase the estimation noise. In addition, the algorithm can effectively reduce the number of error bits in most sampling locations, only in the case of fast angle of arrival, especially in some special scenarios such as arrival area (AAA) and handoff region.
【学位授予单位】：杭州电子科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN92

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