| Wireless communication has been developing rapidly in China in recent years, from 2G to 3G cellular networks. In order to meet the demand of wireless mobile broadband services in next generation,3GPP (3rd Generation Partnership Project) launched the LTE (Long Term Evolution) research project.TD-LTE-Advanced (time division long term evolution) is proposed by China with independent property rights of the new generation mobile communication technology after TD-SCDMA. By 2009, due to its flexibility of spectrum allocation, LTE Obtained the rapid development and wide spread. Until the end of 2013, China has begun the td-scdma LTE formally awarded. The td-scdma LTE-Advanced has become one of the 4G standard of ITU, obtained the 3GPP and widespread support from the United States and Europe many communications companies, such as the chip maker marvels, qualcomm, mediate in Taiwan and so on. AT&T in the United States, Japan NTN, South Korea’s KT, China mobile and Ericsson, nokia, zte, huawei and other equipment manufacturers and operators have said that they would support for TD-LTE. But the td-scdma LTE base station and terminal equipment of the research has just begun, performance testing and verification needs some proprietary equipment. So we need research td-scdma LTE test equipment to study the principle and key technology, promotes the progress, and development of the industry, which has strong practical significance.For any communication system, transmitter transmitting quality is the entire communication system guarantee. EVM entry is an important standard of evaluation communication transmitter signal quality, usually computed by two branches in sampling symbol of IQ samples values. In the transmitter, amplifier, modulator, mixer, power amplifier device’s distortion will affect the EVM entry index, caused a drop in the quality of transmitter, influence the final performance of communication system.This paper first introduces the research background and significance of the development of td-scdma LTE system and the definition of EVM entry and current research state of the subject, as well as the td-scdma LTE system System technical characteristics and advantages, focused on the basis of OFDM technology, especially the comparison of the multiple carrier system and single carrier system, cyclic prefix of OFDM. This paper introduces several kinds of different physical channel and the td-scdma LTE system frame structure. Given the RF test requirements in the 3GPP, in this article, starting from the structure of the transmitter IQ modulation prone to all kinds of mismatch in the process of factors, including the phase mismatch, DC distortion and amplitude mismatch, from the perspective of mathematical theory, analyzed the IQ branch Impact. Analyzes the phase mismatch of IQ in the quantitative influence under QPSK, quantitative analysis of the effects of nonlinear power amplifier to EVM entry; analyze the Time and frequency’s effect, and research different receiver time synchronization and carrier wave synchronization method. For channel estimation, compared the LS, DFT and MMSE. For td-scdma LTE Downlink link, this paper studies the Physical Downlink Shared channel (PDSCH, Physical Downlink Shared Channel), combined with the 3 GPP standards of EVM (error vector magnitude) value calculation method, gives the general uplink and downlink signal EVM test solution, give details The receiving block diagram of hardware structure of EVM test, analyzed the error of measurement. Finally, do simulation in MATLAB platform, in different SNR, compared the different modulation mode EVM entry value, and BER are compared, the results of simulation and theory, have certain reference value in engineering. |
