LTE上下行链路设计与实现

发布时间：2018-07-11 16:50

本文选题：GNU + Radio　；参考：《西安电子科技大学》2014年硕士论文

【摘要】：长期演进项目LTE作为下一代技术标准已经被市场所接受,其主要优点有高速率、宽频谱、低时延等,因此越来越受到研究机构和运营商的重视。本文基于GNU Radio/USRP设计并实现了LTE的上下行链路。本文首先对LTE标准做了简要概述,重点讨论与本文工作相关的标准和技术细节,包括信道译码、链路层的功能、物理层帧格式、物理信道等。其次,基于分层思想,详细阐述了LTE的上下行链路设计,具体来说,将LTE上下行链路分为TUN/TAP、RLC、MAC和物理层等几个功能子层分别设计,其中使用TUN/TAP子层完成IP层与LTE二层/物理层的适配功能,便于支持各种高层业务;使用RLC子层保证数据传输的有序性和有界性;在基站侧的MAC层,设计了上下行调度器,用于对上下行信道资源进行调度分配,在终端侧的MAC层,设计了上行调度请求和状态上报机制,用于上行数据的传输控制;在下行链路的物理层主要设计实现了PBCH、PCFICH、PDCCH、PDSCH信道,上行链路设计实现了PUCCH和PUSCH。然后,使用C++在GNU Radio平台下实现了本文的设计,重点完成以下几点内容:第一,使用MAX_LOG_MAP译码算法完成信道译码,并且对分量译码器输出的外信息进行了缩放处理,避免了信道置信度值的计算,简化了译码器,高斯白噪声信道下的仿真表明,在2dB信噪比、1/2码率条件下,迭代5次误码率可达到10-5;第二,MAC层采用令牌环技术实现了上下行链路资源的简单调度,确定数据传输过程中使用的码块长度、调制方式、带宽分配等参数,并使用调度结果驱动上下行链路子帧的生成与接收;第三,重点分析了系统运行中的时序控制,为了应对软件运行中的时间抖动,论文设置了几个时间裕值来吸收时间抖动,保证系统的稳定、长时间运行,并根据实际测试给出了裕值的设定范围。最后,基于实现的上下行链路模块,在Linux中搭建了IP传输环境进行了功能和性能测试。首先使用ping命令来测试上下行链路的时延,测试表明,ping命令能够正常工作,往返时延基本稳定在135ms左右;其次,使用FTP来测试大业务量下的链路性能,测试表明,FTP能够正常工作,在3MHz带宽无线环境中,使用16QAM调制方式,编码码率为0.7,可以达到下行450KBytes/s的文件传输速率,与理论分析吻合。
[Abstract]:LTE, a long-term evolution project, has been accepted by the market as the next generation technology standard, and its main advantages are high speed, broadband spectrum, low delay and so on, so it has been paid more and more attention by research institutions and operators. This paper designs and implements the uplink and downlink of LTE based on GNU Radio / USRP. This paper first gives a brief overview of the LTE standard, focusing on the standards and technical details related to this work, including channel decoding, link layer function, physical layer frame format, physical channel and so on. Secondly, based on the idea of layering, the design of LTE uplink and downlink is described in detail. Specifically, the LTE uplink and downlink are divided into several functional sub-layers, such as the functional sub-layer of the TUN-P / TCP RLCO MAC and the physical layer. TUN-tap sub-layer is used to complete the adaptation function between IP layer and LTE layer 2 / physical layer, which is convenient to support various high-level services; RLC sublayer is used to ensure the order and boundedness of data transmission; the MAC layer on the base station side is designed, and an uplink and downlink scheduler is designed. In the MAC layer of terminal side, the uplink scheduling request and status report mechanism are designed to control the transmission of uplink data, and the physical layer of downlink is mainly designed to implement the PBCH-PCFICHH / PDCCH PDSCH channel, which is used for the allocation of uplink and downlink channel resources, and the mechanism of uplink scheduling request and status report is designed for the uplink data transmission control. Uplink design and implementation of PUCCH and PUSCH. Then, using C to implement the design of this paper on GNU Radio platform, the following contents are emphatically completed: first, the channel decoding is accomplished by using MAXL _ LOGMAP decoding algorithm, and the output information of the component decoder is scaled and processed. The calculation of channel confidence value is avoided, and the decoder is simplified. The simulation of Gao Si white noise channel shows that under the condition of 2dB SNR / 1 / 2 bit rate, The second MAC layer uses token ring technology to realize the simple scheduling of upstream and downlink resources, and determines the parameters of block length, modulation mode, bandwidth allocation and so on, which are used in the process of data transmission. The scheduling results are used to drive the generation and reception of subframes in the uplink and downlink. Thirdly, the timing control in the system operation is analyzed. In order to deal with the time jitter in the software operation, several time margin values are set up to absorb the time jitter. The system is stable and running for a long time, and the range of margin is given according to the actual test. Finally, based on the realized uplink and downlink module, the IP transmission environment is built in Linux for function and performance testing. First, the ping command is used to test the delay of the uplink and downlink. The test shows that the ping command can work normally, and the round-trip delay is basically stable at about 135ms. Secondly, the ping is used to test the link performance under the large traffic. The test results show that the FTP can work normally. In the 3MHz bandwidth wireless environment, using 16QAM modulation mode, the coding rate is 0.7, which can achieve the downlink 450 KBytes / s file transfer rate, which is 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】：2014
【分类号】：TN929.5

【相似文献】