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An Improved DMRS Design Scheme of LTE-Advanced Uplink
Xiaowen Li,Youbo Feng,Dan Wang 보안공학연구지원센터 2015 International Journal of Smart Home Vol.9 No.4
The 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) uplink supports only a single antenna transmission. However, in order to improve the uplink spectrum efficiency, support multiple antenna transmission in LTE-Advanced. Meanwhile, taking into account backwards compatibility for LTE. LTE-Advanced De-Modulation Reference Signal (DMRS) needs to be designed [1]. According to requirement of LTE-Advanced uplink pilot design, introducing orthogonal cover code (OCC) as a supplement, analysis and study of the current problems, proposes a Circular Shift (CS), Group/Sequence Hopping (GSH) and the OCC joint instructions method of pilot design. Finally, simulation and analysis of the performance of this scheme. Results show that this scheme can meet LTE- Advanced demand for pilot design well.
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Improved Carrier Frequency Offset Estimation Algorithms for PUCCH Format 1 in LTE-Advanced
Dan Wang,Youbo Feng,Yiming Lin 보안공학연구지원센터 2015 International Journal of Signal Processing, Image Vol.8 No.9
Physical Uplink Control Channel (PUCCH) is an important narrow-band channel in LTE-Advanced system, which carries the uplink control information, such as acknowledge/non-acknowledge (ACK/NACK) bits, downlink channel quality indicator (CQI), HARQ-ACK feedback information, and it requires much higher transmission quality than the other channels. With the aid of orthogonal CDMA, multiple users share the same time-frequency resource, the multiuser interference has been the main factor that limits the transmission quality of the control information [1]. In the high-speed mobile scenario, there exists a large Doppler frequency shift, which leads to loss of code orthogonality and also introduces inter-carrier interference (ICI) within a single SC-FDMA symbol. Besides, the multiuser interference in high-speed mobile environment is severe. In this paper, the carrier frequency offset estimation algorithms are analyzed, and a double-iteration carrier frequency offset (CFO) estimation algorithm is proved to perform the best for PUCCH Format 1 in high-speed mobile scenario. The estimation process is achieved by coarse estimation and fine estimation, which enlarges the estimation range and improves the estimation accuracy.
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Study on numerical methods for transient flow induced by speed-changing impeller of fluid machinery
Dazhuan Wu,Tao Chen,Youbo Sun,Wentao Cheng,Leqin Wang 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.6
In order to establish a reliable numerical method for solving the transient rotating flow induced by a speed-changing impeller, two numerical methods based on finite volume method (FVM) were presented and analyzed in this study. Two-dimensional numerical simulations of incompressible transient unsteady flow induced by an impeller during starting process were carried out respectively by using DM and DSR methods. The accuracy and adaptability of the two methods were evaluated by comprehensively comparing the calculation results. Moreover, an intensive study on the application of DSR method was conducted subsequently. The results showed that transient flow structure evolution and transient characteristics of the starting impeller are obviously affected by the starting process. The transient flow can be captured by both two methods, and the DSR method shows a higher computational efficiency. As an application example, the starting process of a mixed-flow pump was simulated by using DSR method. The calculation results were analyzed by comparing with the experiment data.
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Binyu Wang,Jianpeng Wang,Dingkun Ma,Laili Wang,Fengtao Yang,Xinying Li,Youbo Tan 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
Due to a series of advantages compared with other existing power converters, modular multilevel converters (MMCs) have been widely used in the last decade. However, in some applications, such as the offshore wind power transmission, the MMC submodules (SMs) are subjected to harsh operating environment and adverse mission profiles which can easily lead to failures in the solder layers of IGBT modules. Therefore, the lifetime estimation is very important to predict the reliability of MMC. This paper studies the fundamental-frequency thermal cycles and proposes a lifetime estimation method of MMC SMs based on the combination of finite element analysis (FEA) and the physical lifetime model. This method provides a deeper physical description of the failure mechanism and considers the thermal coupling among the chips, which make the lifetime calculation more accurate. The simulation time of FE in this research is acceptable. The distribution of lifetime is presented in the form of a colorful cloud map, rather than a single number, from which we can know the most vulnerable part of the solder layers. This can help us find the appropriate measures to improve the reliability of MMC SMs. In this paper, the principle and reliability issues of MMC are first analyzed. Second, the loss of the SM is calculated through simulation and curve fitting. Then, a 3D finite element (FE) model of MMC SM is developed and the FE simulation is performed. Finally, the lifetime of the SM is obtained based on the FEA results and Morrow lifetime model.
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