LTE系统中上下行同步研究与实现

发布时间：2019-06-21 06:25

【摘要】：移动通信在近三十多年来发展迅速,尤其3GPP提出的“准4G”标准LTE更是近几年的研究热点。为提高频谱利用率,LTE中采用了OFDM技术,然而OFDM技术对时频偏差的敏感,使时频同步技术成为LTE通信过程中一个巨大的挑战。本文基于Linux系统中的开源软件无线电平台GNU Radio与USRP研究LTE中的上下行同步过程。论文首先分析了LTE的基带传输技术基础。包括LTE中的上下行调制传输方式、基本的帧结构以及相应物理信道的处理流程,此外还介绍了LTE中为解决时频偏差而引入的导频信号序列,包括主辅同步序列(PSS, SSS)和参考符号序列(RS)。其次在分析时频偏差对系统影响的基础上分别研究并设计了上下行同步方案。第一、设计下行时频同步方案,主要包括利用PSS与SSS序列完成定时粗同步与频率粗同步,完成小区搜索功能；利用RS信号进行信道估计与均衡,同时利用信道估计结果进行系统残余定时偏差、残余频率偏差的估计,并完成时频误差调整及补偿,以此完成下行追踪过程的同步。第二、设计上行同步方案,主要包括在eNB侧利用上行SRS进行上行时间提前量的估计,并通过TA指令控制UE侧进行样点调整以完成上行定时同步；此外,在UE侧还通过频偏预补偿来完成上行频率同步。第三、设计上下行之间的同步方案,在UE侧以下行定时同步为基础计算下行接收时刻表,作为上行发送时刻的基准,并结合TA过程使所有UE发送数据到达eNB的帧起始时刻一致,完成上下行间同步。第四、针对GNU Radio平台给出LTE中系统同步的整体流程。最后使用C++语言在GNU Radio平台上实现了本文提出的LTE系统同步方案,并分别在室内无线环境与莱斯仿真信道下进行测试。测试结果表明：第一、在无线传输环境中,下行捕获时间在0.35s～0.45s之内,并且稳定工作后子帧处理时间约为0.25ms～0.31ms,证明本论文设计的同步方案能够完成并保证接收数据的正确、实时处理；第二、在无线环境中,系统残余定时偏差与残余频率偏差均在5ms内完成收敛；第三、在多径仿真信道中,SNR为0dB时,定时位置误检概率低于10%,残余定时偏差小于10-2,残余频率偏差小于10-3,并且SNR为6dB时定时位置检测无差错。
[Abstract]:Mobile communication has developed rapidly in recent 30 years, especially the "quasi-4G" standard LTE proposed by 3GPP is a hot research topic in recent years. In order to improve the spectrum efficiency, OFDM technology is used in LTE. However, the sensitivity of OFDM technology to time-frequency deviation makes time-frequency synchronization technology become a great challenge in the process of LTE communication. In this paper, based on the open source software radio platform GNU Radio and USRP in Linux system, the uplink and downlink synchronization process in LTE is studied. Firstly, the basis of baseband transmission technology of LTE is analyzed. It includes the uplink and downlink modulation transmission mode in LTE, the basic frame structure and the processing flow of the corresponding physical channel. In addition, the pilot signal sequence introduced in LTE to solve the time-frequency deviation is also introduced, including the primary and auxiliary synchronization sequence (PSS, SSS) and the reference symbol sequence (RS). Secondly, based on the analysis of the influence of time-frequency deviation on the system, the uplink and downlink synchronization schemes are studied and designed. Firstly, the downlink time-frequency synchronization scheme is designed, which mainly includes using PSS and SSS sequences to complete timing rough synchronization and frequency rough synchronization, completing cell search function, using RS signal to estimate and equalize the residual timing deviation and residual frequency deviation, and completing the adjustment and compensation of time-frequency error, so as to complete the synchronization of downlink tracking process. Secondly, the uplink synchronization scheme is designed, which mainly includes the estimation of uplink time advance by using uplink SRS on the eNB side, and the sample point adjustment through TA instruction to complete uplink timing synchronization; in addition, the uplink frequency synchronization is completed by frequency offset pre-compensation on the UE side. Thirdly, the synchronization scheme between uplink and downlink is designed, and the downlink receiving schedule is calculated on the basis of row timing synchronization below UE side, which is used as the reference of uplink transmission time, and the frame starting time of all UE transmission data arriving at eNB is consistent with TA process, and the synchronization between up and down lines is completed. Fourth, the overall process of system synchronization in LTE is given for GNU Radio platform. Finally, the synchronization scheme of LTE system proposed in this paper is implemented on GNU Radio platform with C language, and tested in indoor wireless environment and Rice simulation channel respectively. The test results show that: first, in the wireless transmission environment, the downlink acquisition time is within 0.35s~0.45s, and the subframe processing time after stable operation is about 0.25ms 鈮，

本文编号：2503861