Modified Volterra Series Models for Behavioral Modeling of RF Power Amplifier with Memory Effects

Hoki Kim,Kyunghoon Kim,Jinwook Burm 대한전자공학회 2009 ITC-CSCC :International Technical Conference on Ci Vol.2009 No.7

In this paper, a behavior modeling method which is considered with memory effects of nonlinear RF power amplifiers is proposed. A modeling method distinguished from other simplified modeling methods based Volterra series is presented, which is designed with two blocks. One is the nonlinear block and the other is the linear block. To take into account memory effects, the linear block is designed by using delay taps. Power amplifiers modeled in this paper are WCDMA which used AWT6282 manufactured by ANADIGICS respectively. The data adopted in modeling is based on the collected data in WCDMA 1700㎒ Band measured by a signal analyzer. Modeling is designed with MATLAB program and simulated in Time-domain and Frequency-domain. Using the compensation methods, the proposed model successively predicted the power amplifier behavior within about 2 ㏈ accuracy.

Beacon-Based Slotted ALOHA for Wireless Networks with Large Propagation Delay

Hoki Baek,Jaesung Lim,Sangyoon Oh IEEE 2013 IEEE communications letters Vol.17 No.11

<P>In a wireless network with large propagation delay S-ALOHA(Slotted ALOHA) requires large guard time which causes lower normalized throughput. To reduce the large guard time in the ISA-ALOHA, a time alignment mechanism was proposed under the assumption of propagation delay estimation. In this letter, we propose a framed structure which is able to estimate propagation delay by employing coordinator beaconing. The framed structure consists of a time period for beaconing and a group of multiple time slots for random access. The proposed Beacon-based S-ALOHA(BS-ALOHA) can make packets generated during the time of beaconing evenly distributed over the random access period. Furthermore, we propose an analytical model considering overhead due to coordinator beaconing time and show that BS-ALOHA provides higher normalized throughput than both ALOHA and S-ALOHA employing the large guard time.</P>

Differential Item Functioning of an ESL Placement Exam for the Examinees with Different Academic Disciplines

Hoky Min 한국응용언어학회 2011 응용 언어학 Vol.27 No.4

The present research examines differential item functioning (DIF) of an ESL placement exam for the examinees with different academic disciplines using two DIF detection methods: the Mantel-Haenszel(MH) and logistic regression procedures. Findings indicated that no item showed large DIF in the MH procedure but one item showed uniform DIF and two items showed non-uniform DIF in the logistic regression procedure. The items flagged for DIF were not considered biased against students with particular academic backgrounds, however. The content expert panels shared the idea that the language in those items is not only domain specific but also part of general academic vocabulary that college students should know. In other words, knowledge of the language in the items flagged for DIF can be considered to be part of the construct being measured in the test. Consequently, it was judged that the difference in difficulty between the two groups of those items was attributed to a legitimate reading ability difference. Finally, validity of the ESLPE score interpretation, decision and consequences was also discussed.

Design of Future UAV-Relay Tactical Data Link for Reliable UAV Control and Situational Awareness

Baek, Hoki,Lim, Jaesung Institute of Electrical and Electronics Engineers 2018 IEEE communications magazine Vol.56 No.10

<P>Unmanned aerial vehicles (UAVs) have recently been widely used in the military and commercial domains. UAVs, especially in the military domain, were initially used for gathering intelligence, surveillance, and reconnaissance data, and sending them to a command center. Their use was then expanded to the tactical level to perform military operations with manned platforms. Operating a UAV as a relay node in the air has many advantages, including coverage, recovery from disconnection from a relay, clear communication channel, and easy deployment. Thus, the UAV-Relay tactical network can support more effective military operations. However, reliable UAV control and situational awareness must be guaranteed for the use of tactical UAVs. In other words, all tactical nodes must be able to send their location and status periodically under the dynamic and unexpected situation of a battlefield. However, a jamming attack from the enemy can make UAV control and situational awareness impossible. Thus, we need a robust tactical data link (TDL) to guarantee reliable UAV control and situational awareness under a jamming attack. In this article, we first explain the requirements for reliable UAV control and situational awareness. We then design a future UAV-relay TDL, called link-situational awareness and control (Link-SAC), which satisfies the requirements. We also deal with the spectrum allocation and management of Link-SAC because Link-SAC requires large bandwidth under the scarcity of spectrum resource. Thus, we consider spectrum sharing to allocate an X-Band uplink to Link-SAC. Based on the interference analysis in a prior study, we show that spectrum sharing is possible. We also show how Link-SAC can manage the spectrum. Lastly, we present our concluding remarks.</P>

500kV HVDC XLPE 지중송전 케이블 육상 시공을 위한 측압시험 실증 사례

김호기(Hoki Kim),김동규(Dongkyu Kim),박진우(Jinwoo Park),임진규(Jinkyu Lim),신승준(Seungjoon Shin),신용재(Yongjae Shin) 대한전기학회 2023 대한전기학회 학술대회 논문집 Vol.2023 No.7

500kV HVDC XLPE 지중송전 케이블 육상 시공을 위한 측압시험 실증 사례

김호기(Hoki Kim),김동규(Dongkyu Kim),박진우(Jinwoo Park),임진규(Jinkyu Lim),신승준(Seungjoon Shin),신용재(Yongjae Shin) 대한전기학회 2023 대한전기학회 학술대회 논문집 Vol.2023 No.7

Structural Seismic Design Optimization and Earthquake Engineering

반호기(Hoki Ban) 대한토목학회 2018 대한토목학회지 Vol.66 No.1

Link-16에서 이미지 전송을 위한 신뢰성 기반의 동적 TDMA 기법과 새로운 패킹 방법

백호기(Hoki Baek),임재성(Jaesung Lim),구자열(Jayeul Koo),진정환(Jeonghwan Jin),전필성(Philseong Chun),오일혁(Ilhyuk Oh) 한국통신학회 2012 韓國通信學會論文誌 Vol.37 No.11(융합기술)

Link-16은 가장 널리 사용 중인 전술데이터링크로써 TDMA(Time Division Multiple Access)를 기반으로 동작한다. Link-16은 안정적이지만 전송 속도가 매우 낮아 전술 메시지, 음성 등 작은 사이즈의 데이터 전송을 지원한다. 그러나 최근 효과중심작전(EBO: Effect-Based Operation)에 대한 관심이 증가하면서, Link-16을 통해 이미지와 같은 상황 인식 정보를 전송하려는 동향이 있다. 이미지는 기존 메시지에 비해 크기가 매우 크기 때문에 Link-16의 Static TDMA가 아닌 별도의 TDMA 스케줄링이 필요하다. 따라서 본 논문에서는 Link-16의 MAC을 진화시킨 Link-16K를 제안하였다. Link-16K는 Link-16과 호환성을 유지한다. 그리고 이미지 전송을 효과적으로 지원하기 위해 DTDMA(Dynamic TDMA), 새로운 재전송 방법, 새로운 패킹 방법을 포함한다. 제안하는 아이디어의 시뮬레이션 결과를 통해 이미지 전송 시간이 단축되었고, 채널 효율성이 높아졌음을 확인하였다. Link-16 is a widely used TDL (Tactical Data Link) which uses TDMA (Time Division Multiple Access). Link-16 is a very low rate system, so it supports small size of data like tactical message and voice. However, there are related works to transmit situation awareness information like image due to the increasing interest about EBO(Effect-Based Operation), recently. Special TDMA scheduling is needed not static TDMA of Link-16 for image transmission because image data has much larger size than the existing tactical data. In this paper, we proposed Link-16K which enhances the Link-16 MAC. The proposed Link-16K is compatible with Link-16, and includes dynamic TDMA, new packing method, and an efficient retransmission scheme for image transmission effectively. We can see that image transmission delay is reduced and channel utilization is increased through simulation results of proposed idea

Spectrum Sharing for Coexistence of Fixed Satellite Services and Frequency Hopping Tactical Data Link

Baek, Hoki,Lim, Jaesung IEEE 2016 IEEE journal on selected areas in communications Vol.34 No.10

<P>The growth in wireless communication services together with increasing demand has resulted in the scarcity of spectrum resources. Many researchers have attempted to address the scarcity problem by focusing on spectrum sharing to allow fixed satellite services (FSS) to coexist with other fixed services or other satellite communication systems. However, most secondary users are commercial systems, whose characteristics differ from military systems such as tactical data links (TDLs). A TDL requires anti-jamming capability and multiple operations support; thus, most TDLs use multiple frequency hopping (FH) patterns, known as multinet. To the best of our knowledge, no research has focused on the coexistence of FSS and TDL to date. In this paper, we verify whether spectrum sharing will facilitate the coexistence of FSS and FH-TDL. First, we propose FH-TDL with a spectrum use rule and a new FH method to reduce the pulse collision probability. We then prove that interference from FH-TDL to FSS is permissible. Instead of analyzing interference from FSS to FH-TDL, we simply consider the worst case, i.e., that a signal experiencing interference by FSS is always subject to collisions. We analyze the pulse collision probability under the worst case by constructing the mathematical models rather than using simulation. The numerical results show that the use of appropriate values for the weight parameter enables the proposed FH method to improve the pulse collision probability of FH-TDL.</P>

전파 지연이 긴 공중 전술 TDMA 네트워크에서 송신자 간 거리 기반 보호 시간 제어 기법

백호기(Hoki Baek),임재성(Jaesung Lim),구자열(Jayeul Koo),오일혁(Ilhyuk Oh) 한국통신학회 2012 韓國通信學會論文誌 Vol.37 No.11(융합기술)

공중 전술 네트워크는 공대공 또는 공대지 작전에 사용되고 전파 지연이 크다는 특징이 있다. 모든 노드는 TDMA 기반의 브로드캐스팅을 사용하여 데이터를 공유한다. 공중 전술 네트워크에서는 긴 전파 지연으로 인한 충돌 때문에, 브로드캐스팅을 보장하기 위해서는 각 타임 슬롯마다 보호 시간이 필요하다. 그러나 보호 시간의 낭비로 인해 네트워크의 채널 이용률이 크게 저하될 수 있다. 본 논문에서는 송신자 간 거리 정보를 사용하여 보호 시간의 낭비를 줄여 채널 이용률을 향상시키면서 브로드캐스팅을 보장하는 Inter-Transmitter Distance-Based TDMA(ID-TDMA) 기법을 제안한다. 그리고 성능 평가를 통해 ID-TDMA의 효과성을 확인하였다. Airborne tactical networks is used to air-to-air or air-to-ground operation and have a large propagation delay. All nodes share the data by using TDMA-based broadcasting. In airborne tactical networks, each time slot needs the guard time to ensure the broadcasting because the collisions occur due to the large propagation delay. However, the channel utilization of the networks can be greatly degraded due to the waste of guard time. In this paper, we propose Inter-Transmitter Distance-Based TDMA (ID-TDMA) scheme which ensures the broadcasting while improving the channel utilization by reducing the guard time with the inter-transmitter distance information. The proposed scheme shows the effectiveness through the performance evaluation.