TD-LTE系统下行PDSCH信道EVM测试研究

发布时间：2018-09-19 18:09

【摘要】：近年来我国无线通信发展迅速,从2G到3G蜂窝网络,同时又为了满足下一代无线移动宽带业务需求。从90年代开始,LTE研究项目就被3GPP (3rd Generation Partnership Project)提出了。我国在3G标准TD-SCDMA之后,紧接着又提出了拥有自主产权的新一代移动通信技术TD-LTE-Advanced(分时长期演进)。截止到2009年LTE商用以来,由于其频谱配置的灵活性,使其得到了飞速的发展和广泛的传播,直到2013年底,中国已经开始正式发放TD-LTE牌照。TD-LTE-Advanced已经成为了国际电联ITU的4G标准之一,得到了3GPP、美国和欧洲许多移动通信公司的大力支持,比如美国的芯片厂商marvell、高通,台湾的联发科等等。美国的ATT、日本的NTN、韩国的KT、中国移动以及爱立信、诺基亚、中兴、华为等电信设备制造商以及运营商明确表示了支持TD-LTE。但是TD-LTE的基站和终端设备的研制才刚刚开始,性能的测试和验证需要一些专有的仪器。因此我们需要对TD-LTE的测试设备的原理和关键技术进行研究,有助于推动这个产业的进步和发展,具有很强的现实意义。对于任何通信系统,发射机的发射质量好坏是整个通信系统的保证。EVM是评估通信发射机发射信号质量的重要标准,一般通过在采样符号的IQ两个支路的采样值来完成。在发射机中,放大器、调制器、混频器以及功率放大器等器件的不理想都会影响EVM指标,造成发射质量的下降,影响通信系统的最终性能。本文首先介绍了课题的研究背景和意义,介绍了TD-LTE系统的发展以及EVM的定义和目前该课题的研究状况,以及TD-LTE系统的技术特点和优势,重点阐述了OFDM技术的基础,特别是多载波系统和单载波系统的比较,OFDM的循环前缀等关键技术。分类介绍了几种不同的物理信道以及TD-LTE系统的帧结构。给出了3GPP中的测试要求,从发射机的结构出发,分析了在IQ调制的过程中容易出现的各种失配因素,包括相位失配,直流失配以及幅度失配,从数学理论的角度,分析了IQ的相位失配在QPSK下的定量影响,定量分析了功率放大器的非线性对EVM的影响；给出了时频不同步对EVM指标的影响,研究了不同的接收机时间同步和载波同步方法。对于信道估计,比较了LS、DFT以及MMSE这三种信道估计算法的理论依据和性能曲线。针对TD-LTE下行链路,着重研究了物理下行共享信道(PDSCH Physical Downlink Shared Channel),结合3GPP标准规定的EVM(误差向量幅度)值的计算方法,给出了通用的上行和下行信号EVM测试方案,详细给出了EVM测试的接收框图硬件结构,分析了测量误差。最后,在MATLAB仿真环境下,在不同的信噪比,对比了不同调制方式下的EVM值,与BER进行了对比,仿真结果和理论相符合,具有一定的工程参考价值。
[Abstract]:In recent years, China's wireless communication has developed rapidly, from 2G to 3G cellular networks, and to meet the needs of the next generation of wireless mobile broadband services. Since 1990's, the research project of LTE has been put forward by 3GPP (3rd Generation Partnership Project). Following the 3G standard TD-SCDMA, a new generation of mobile communication technology TD-LTE-Advanced (time-sharing long term evolution) with independent property rights is proposed. Since the commercial use of LTE in 2009, because of the flexibility of its spectrum configuration, it has been rapidly developed and widely disseminated. Until the end of 2013, China has officially issued the TD-LTE license. TD-LTE-Advanced has become one of the 4G standards of ITU. It has strong support from 3GPP, the United States and many European mobile companies, such as marvell, Qualcomm, an American chipmaker, and MediaTek in Taiwan. Us ATT, Japan NTN, Korea KT, China Mobile and Ericsson Nokia ZTE Huawei and other telecom equipment manufacturers and operators have made clear their support for TD-LTE. But the development of TD-LTE base station and terminal equipment is just beginning. Some proprietary instruments are needed for performance test and verification. Therefore, we need to study the principle and key technology of TD-LTE test equipment, which is helpful to promote the progress and development of this industry. For any communication system, the transmitting quality of transmitter is the guarantee of the whole communication system. EVM is an important standard to evaluate the signal quality of communication transmitter. In the transmitter, the imperfect of amplifiers, modulators, mixers and power amplifiers will affect the EVM index, resulting in the deterioration of the quality of transmission and the final performance of the communication system. This paper first introduces the research background and significance of the subject, introduces the development of TD-LTE system, the definition of EVM and the current research status of the subject, and the technical characteristics and advantages of TD-LTE system, and emphasizes on the basis of OFDM technology. Especially the comparison between multi-carrier system and single-carrier system, such as cyclic prefix of OFDM and so on. Several different physical channels and frame structure of TD-LTE system are introduced in this paper. The test requirements in 3GPP are given. Starting from the structure of transmitter, various mismatch factors, including phase mismatch, DC mismatch and amplitude mismatch, are analyzed in the process of IQ modulation. The quantitative effect of phase mismatch of IQ on QPSK is analyzed, the influence of nonlinear power amplifier on EVM is quantitatively analyzed, the influence of time-frequency nonsynchronization on EVM index is given, and different methods of receiver time synchronization and carrier synchronization are studied. For channel estimation, the theoretical basis and performance curve of three channel estimation algorithms, LS,DFT and MMSE, are compared. Aiming at the downlink of TD-LTE, the calculation method of (PDSCH Physical Downlink Shared Channel), (error vector amplitude) of physical downlink shared channel combined with EVM (error vector amplitude) specified by 3GPP standard is studied emphatically, and a general EVM test scheme for uplink and downlink signals is given. The hardware structure of receiving block diagram of EVM test is given in detail, and the measurement error is analyzed. Finally, in the MATLAB simulation environment, under different SNR, the EVM values of different modulation modes are compared and compared with BER. The simulation results are consistent with the theory, and have certain engineering reference value.
【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

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