Seunghoon Lee

Analog beamforming technology is being used to overcome various technical drawbacks of mm-wave wireless communications systems. However, the errors caused by circuit implementations, quantized control, and imperfect isolation between antenna elements result in radiation pattern (RP) distortion and performance deterioration. In particular, the quantization error and mutual coupling cause the active reflection coefficient (ARC) of each antenna element to vary with respect to the main beam directio

As machine learning (ML) has been proven effective in solving various problems, researchers in the real-time systems (RT) community have recently paid increasing attention to ML. While most of them focused on timing issues for ML applications (i.e., RT for ML), only a little has been done on the use of ML for solving fundamental RT problems. In this paper, we aim at utilizing ML to solve a fundamental RT problem of priority assignment for global fixed-priority preemptive (gFP) scheduling on a mu

A new current reused quadrature voltage controlled oscillator (QVCO) is proposed and implemented using UMC 0.18 μm CMOS 1P6M process. The proposed circuit topology is made up two low voltage LC-tank VCOs, where the QVCO is obtained using the transformer coupling and current reuse technique. At 1.8 V supply voltage, the phase noise of the VCO is -117.13 dBc/Hz at 1 MHz offset frequency from the carrier frequency of 2.18GHz, the core power consumption is 4.14mW, the total power consumption is 6.48

The Terahertz (THz) band, encompassing a range from 0.1 to 10 THz, has attracted research interest due to its expansive frequency bandwidth and minimal hardware footprint requirements. Unfortunately, the output power of transmitter (TX) in the THz band is low, while the free-space path loss is high, resulting in an short operating range for wireless communication systems [1]. The THz communication via a low-loss plastic waveguide emerges as a formidable alternative to existing solutions such as

In millimeter-wave wireless communications systems, analog beamforming technology is being used to overcome technical drawbacks such as limited service coverage, high atmospheric loss, and insufficient signal-to-noise ratios. However, the errors caused by circuit implementation, quantized control, and imperfect isolation between antenna elements result in radiation pattern distortion and performance deterioration. In this work, we derived the statistical behavior of radiation pattern distortion

Federated learning over wireless networks requires aggregating locally computed gradients at a server where the mobile devices send statistically distinct gradient information over heterogenous communication links. This paper proposes a Bayesian approach for wireless federated learning referred to as soft-sign stochastic gradient descent (soft-signSGD). The idea of soft-signSGD is to aggregate the one-bit quantized local gradients at the server by jointly exploiting i) the prior distributions of

The bipolar dc grid has many advantages compared with the unipolar dc grid. The triple-active-bridge (TAB) converter is a popular topology to implement the bipolar dc grid due to its dual-output structure. However, the voltage imbalance caused by the asymmetric load condition is a major issue. This study proposes an integrated transformer to achieve voltage balancing in the TAB converter without the need for any additional balancer circuits or dedicated control schemes. In this study, the high-f

This brief presents an I/Q imbalance calibration scheme for a 5G direct-conversion transmitter (TX). By utilizing a simple 1-bit phase-to-digital converter and 9-bit digital-to-analog converter, a quadrature phase error associated with fabrication tolerances can be minimized effectively using a binary search algorithm. This approach implements a continuous, real-time calibration that adaptively adjusts the resistive components of the type-I polyphase filter in response to detected phase errors,

본 논문에서는 프로그램 선택 소자는 채널 폭이 큰 NMOS (N-channel MOSFET) 트랜지스터 대신 DNW (Deep N-Well) 안에 형성된 채널 폭이 작은 isolated NMOS 트랜지스터의 body인 PW (P-Well)과 source 노드인 n+ diffusion 영역 사이에 형성된 기생하는 접합 다이오드를 사용하는 NMOS-Diode eFuse OTP (One-Time Programmable) 셀을 제안하였다. 제안된 eFuse OTP 셀은 프로그램 모드에서 NMOS 트랜지스터에 형성되는 기생하는 접합 다이오드를 이용하여 eFuse를 blowing 시킨다. 그리고 읽기 모드에서는 접합 다이오드를 이용하는 것이 아니고 NMOS 트랜지스터를 이용하기 때문에 다이오드의 contact voltage 강하를 제거할 수 있으므로 ‘0’ 데이터에 대한 센싱불량을 제거할 수 있다. 또한 읽기 모드에서 채널 폭이 작은 NMOS 트랜지스터를 이용하여 BL에 전압을 전달하므로 OT

CAD systems which are used in ship design are variety among different usage and purpose. So designed data exchange between CAD systems is needed from different formats during stage of ship. Because of every CAD system has its own format inside, data exchange between them is difficult to implement. Many parts of ship design data exchange are worked by many designers at present. So design expense and man-hour are increasing in proportion to extension of ship industry. In this paper, we discuss abo