基于GNU Radio的FDD-LTE上行多用户系统设计与实现

发布时间：2018-07-20 09:22

【摘要】：在LTE上行链路中,由于叠加在一起的不同用户的信号定时偏移和频率偏移各不相同,因此上行同步需要估计多个参数,如何同时对不同用户进行补偿是一个难点。论文首先对LTE系统重点介绍了与本论文工作相关的知识,包括系统帧结构、上行调制技术、上行通信信道、基带信号处理流程,此外还介绍了LTE系统上行同步所用到的关键序列以及上行多用户系统特点与子载波资源分配方式。其次,基于已实现的LTE演示系统,针对其每个上行子帧只能传输一个终端数据的问题,详细讨论了基站侧多用户并发功能的改进设计,从而支持在单个上行子帧内同时传输多个终端的数据。具体包括:第一,将上行调度由时分复用的轮询调度修改成了频分复用的子载波块状分配;第二,用“多路并行处理+资源解映射”而非窄带滤波器组的方式来分离上行多用户的数据;第三,设计了适合上行多用户系统的上行时频同步方案。在时频同步方案中,利用DMRS信号进行上行时间提前量(TA)的估计,并控制终端进行样点调整以维持上行定时同步;分别利用SRS信号和DMRS信号进行粗频偏估计和残余频偏估计,并相应在FFT前进行频偏补偿,以完成上行频率同步。在多径仿真信道下对所实现同步模块的仿真结果表明,五个用户同时通信,定时估计算法在高斯信道下性能优于多径信道;联合频偏估计算法在高斯信道下性能与多径信道类似。然后,本文基于GNU Radio/USRP软硬件平台和已有LTE演示系统实现了上述设计。第一,实现了上行多用户的资源调度,可在同一子帧对多个终端的请求进行调度,提高了效率和频带利用率。第二,实现了所设计的上行同步方案,包括频偏补偿和UE定时调整的实现;此外,在用SRS和DMRS进行偏差估计时分别引入了SRS互相关算法和CRC校验,从而提高了偏差估计值的准确度和有效性。第三,基于GNURadio的平台特点和信号驱动的流图机制,搭建出完整的可支持上行多用户时频同步与信号处理的LTE无线通信实际系统。最后,在室内无线环境下对该系统进行了实测。结果表明,基站能够同时调度两个终端的请求,也能够同时接收两个终端所发送的视频流;在3MHz带宽无线环境中,使用QPSK调制方式,上行编码码率为0.5条件下,平均上行误包率为1.3×10-5,播放视频的主观质量清晰流畅;两终端可以达到227.6KBytes/s的总上行速率,与理论分析基本吻合。
[Abstract]:In the LTE uplink, because the signal timing offset and frequency offset of different users superimposed together are different, uplink synchronization needs to estimate multiple parameters, so how to compensate different users at the same time is a difficulty. Firstly, the thesis introduces the knowledge of LTE system, including system frame structure, uplink modulation technology, uplink communication channel, baseband signal processing flow. In addition, the key sequences used in uplink synchronization of LTE system and the characteristics of uplink multiuser system and subcarrier resource allocation are also introduced. Secondly, based on the implemented LTE demonstration system, aiming at the problem that only one terminal data can be transmitted per uplink sub-frame, this paper discusses in detail the improved design of multi-user concurrent function on the base station side. Thus, the data of multiple terminals can be transmitted simultaneously in a single uplink subframe. Specifically including: first, the uplink scheduling is modified from the polling scheduling of time division multiplexing to subcarrier block allocation of frequency division multiplexing; second, The data of uplink multiuser is separated by "multi-channel parallel processing resource demapping" instead of narrowband filter bank. Thirdly, an uplink time-frequency synchronization scheme suitable for uplink multiuser system is designed. In the time-frequency synchronization scheme, DMRS signal is used to estimate the uplink time advance (TA), and the terminal is controlled to adjust the sample points to maintain the uplink timing synchronization, and the SRS and DMRS signals are used to estimate the coarse frequency offset and the residual frequency offset, respectively. Frequency offset compensation is carried out before FFT to achieve uplink frequency synchronization. The simulation results of the synchronization module in multipath simulation channel show that the performance of timing estimation algorithm in Gao Si channel is better than that in multipath channel. The performance of joint frequency offset estimation algorithm in Gao Si channel is similar to that in multipath channel. Then, based on GNU Radio / USRP software and hardware platform and LTE demonstration system, the above design is implemented. First, the uplink multi-user resource scheduling is realized, which can schedule the requests of multiple terminals in the same sub-frame, which improves the efficiency and frequency band efficiency. Secondly, the proposed uplink synchronization scheme is implemented, including frequency offset compensation and UE timing adjustment, in addition, SRS cross-correlation algorithm and CRC check are introduced in the estimation of deviation by SRS and DMRS, respectively. Therefore, the accuracy and validity of the deviation estimate are improved. Thirdly, based on the platform characteristics of GNURadio and the signal-driven flow graph mechanism, a complete LTE wireless communication system which can support uplink multi-user time-frequency synchronization and signal processing is built. Finally, the system is measured in indoor wireless environment. The results show that the base station can simultaneously schedule the requests of the two terminals and receive the video streams transmitted by the two terminals at the same time. In the 3MHz bandwidth wireless environment, using QPSK modulation mode, the uplink coding rate is 0.5. The average uplink packet error rate is 1.3 脳 10 ~ (-5), the subjective quality of video playing is clear and smooth, and the two terminals can achieve the total uplink rate of 227.6 KBytes / s, which is basically consistent with the theoretical analysis.
【学位授予单位】：西安电子科技大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TN929.5

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