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Song, Jiho,Choi, Junil,Love, David J. Institute of Electrical and Electronics Engineers 2017 IEEE Transactions on Communications Vol. No.
<P>Fifth generation wireless networks are expected to utilize wide bandwidths available at millimeter wave (mmWave) frequencies for enhancing system throughput. However, the unfavorable channel conditions of mmWave links, such as, higher path loss and attenuation due to atmospheric gases or water vapor, hinder reliable communications. To compensate for these severe losses, it is essential to have a multitude of antennas to generate sharp and strong beams for directional transmission. In this paper, we consider mmWave systems using uniform planar array (UPA) antennas, which effectively place more antennas on a 2-D grid. A hybrid beamforming setup is also considered to generate beams by combining a multitude of antennas using only a few radio frequency chains. We focus on designing a set of transmit beamformers generating beams adapted to the directional characteristics of mmWave links assuming a UPA and hybrid beamforming. We first define ideal beam patterns for UPA structures. Each beamformer is constructed to minimize the mean squared error from the corresponding ideal beam pattern. Simulation results verify that the proposed codebooks enhance beamforming reliability and data rate in mmWave systems.</P>
Advanced Quantizer Designs for FDD-Based FD-MIMO Systems Using Uniform Planar Arrays
Song, Jiho,Choi, Junil,Kim, Taeyoung,Love, David J. Institute of Electrical and Electronics Engineers 2018 IEEE transactions on signal processing Vol.66 No.14
<P>Massive multiple-input multiple-output (MIMO) systems, which utilize a large number of antennas at the base station, are expected to enhance network throughput by enabling improved multiuser MIMO techniques. To deploy many antennas in reasonable form factors, base stations are expected to employ antenna arrays in both horizontal and vertical dimensions, which is known as full-dimensional (FD) MIMO. The most popular two-dimensional array is the uniform planar array (UPA), where antennas are placed in a grid pattern. To exploit the full benefit of massive MIMO in frequency division duplexing, the downlink channel state information (CSI) should be estimated, quantized, and fed back from the receiver to the transmitter. However, it is difficult to accurately quantize the channel in a computationally efficient manner due to the high dimensionality of the massive MIMO channel. In this paper, we develop both narrow-band and wideband CSI quantizers for FD-MIMO taking the properties of realistic channels and the UPA into consideration. To improve quantization quality, we focus on not only quantizing dominant radio paths in the channel, but also combining the quantized beams. We also develop a hierarchical beam search approach, which scans both vertical and horizontal domains jointly with moderate computational complexity. Numerical simulations verify that the performance of the proposed quantizers is better than that of previous CSI quantization techniques.</P>
Jiho Song,Chang-Yeob Chu,Youngseok Lee,Dong-In Lee,Han-Shin Youn,Ki-Bum Park 전력전자학회 2023 ICPE(ISPE)논문집 Vol.2023 No.-
Recently, with SiC devices, switching frequency and electromagnetic interference (EMI) noise are increasing for power factor correction (PFC) converters, and EMI filter is used to reduce EMI noise. However, when EMI filter size is reduced from 2-stage and 1-stage for increasing power density, there is a problem that EMI noise is increasing and EMI standard is no longer satisfied with conventional fixed frequency modulation (FFM). To solve this problem, parameter optimization of spread spectrum modulation (SSM) is performed in this paper. Considering waveform shape, amplitude, and frequency of switching frequency, an optimal switching frequency for minimizing EMI noise is found. As a result, EMI noise is minimized when waveform shape is random and amplitude is 18 kHz, and EMI margin is 11.13 %. Therefore, it is possible to reduce EMI filter size with optimized SSM, and also there is no difference in terms of inductor and switch losses.