• 한국멀티미디어학회논문지
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• 제21권2호
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• pp.188-198
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• 2018

With recent development of high-speed wide-area wireless networks and wide spread of highperformance wireless devices, the demand on seamless video streaming services in Long Term Evolution (LTE) network environments is ever increasing. To meet the demand and provide enhanced Quality of Experience (QoE) with mobile users, the Dynamic Adaptive Streaming over HTTP (DASH) has been actively studied to achieve QoE enhanced video streaming service in dynamic network environments. However, the existing DASH algorithm to select the quality of requesting video segments is based on a procedural algorithm so that it reveals a limitation to adapt its performance to dynamic network situations. To overcome this limitation this paper proposes a novel quality selection mechanism based on a Deep Q-Network (DQN) model, the DQN-based DASH ABR($DQN_{ABR}$) mechanism. The $DQN_{ABR}$ mechanism replaces the existing DASH ABR algorithm with an intelligent deep learning model which optimizes service quality to mobile users through reinforcement learning. Compared to the existing approaches, the experimental analysis shows that the proposed solution outperforms in terms of adapting to dynamic wireless network situations and improving QoE experience of end users.

• ETRI Journal
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• 제36권2호
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• pp.317-320
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• 2014

A balanced RF duplexer with low interference in an extremely narrow bandgap is proposed. The Long-Term Evolution band-7 duplexer should be designed to prevent the co-existence problem with the WiFi band, whose fractional bandgap corresponds to only 0.7%. By implementing a hybrid bulk acoustic wave (BAW) structure, the temperature coefficient of frequency (TCF) value of the duplexer is successfully reduced and the suppressed interference for the narrow bandgap is performed. To achieve an RF duplexer with balanced Rx output topology, we also propose a novel balanced BAW Rx topology and RF circuit block. The novel balanced Rx filter is designed with both lattice- and ladder-type configurations to ensure excellent attenuation. The RF circuit block, which is located between the antenna and the Rx filter, is developed to simultaneously function as a balance-tounbalance transformer and a phase shift network. The size of the fabricated duplexer is as small as $2.0mm{\times}1.6mm$. The maximum insertion loss of the duplexer is as low as 2.4 dB in the Tx band, and the minimum attenuation in the WiFi band is as high as 36.8 dB. The TCF value is considerably lowered to $-16.9ppm/^{\circ}C$.

• 한국정보통신학회논문지
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• 제19권6호
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• pp.1449-1454
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• 2015

자동차 진단 데이터의 양이 증가함에 따라 자동차 에코시스템의 액터는 스마트 자동차에서 수집된 데이터에 따라 새로운 서비스를 시뮬레이션 하거나 설계하기 위하여 실시간으로 분석을 해야 하는 어려움에 직면하게 된다. 본 논문에서는 자동차에서 생성된 막대한 양의 자동차 내장 진단 데이터를 처리하고 분석하는데 필수적이고 심오한 해석학을 제시하는 빅 데이터 솔루션에 관한 연구를 하였다. Hadoop 및 그 에코시스템은 자동차 소유자에 대한 새로운 서비스 제공을 위해 자동차 에코시스템의 액터에 의해 사용될 수 있는 막대한 데이터 및 전달된 유용한 결과를 처리하기 위해 개발된 것이다. 지능형 교통시스템이 안전성 보장, 속도로 인한 사고로 입는 상해 및 충돌의 비율 감소 등에 관여함에 따라, 자동차 진단 데이터 기반의 빅 데이터 솔루션 개발을 통해 향후 실시간 결과 감시, 여러 스마트 자동차에서의 데이터 수집, 수집된 데이터에 대한 신뢰성 있는 처리 및 용이한 저장을 실현화하게 된다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권11호
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• pp.3876-3895
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• 2014

Recently, Heterogeneous Network (HetNet) with Coordinated Multi-Point (CoMP) scheme is introduced into Long Term Evolution-Advanced (LTE-A) systems to improve digital services for User Equipments (UEs), especially for cell-edge UEs. However, Radio Resource Management (RRM), including Resource Block (RB) scheduling and Power Allocation (PA), in this scenario becomes challenging, due to the intercell cooperation. In this paper, we investigate the RRM problem for downlink transmission of HetNet system with Joint Processing (JP) CoMP (both joint transmission and dynamic cell selection schemes), aiming at maximizing weighted sum data rate under the constraints of both transmission power and backhaul capacity. First, joint RB scheduling and PA problem is formulated as a constrained Mixed Integer Programming (MIP) which is NP-hard. To simplify the formulation problem, we decompose it into two problems of RB scheduling and PA. For RB scheduling, we propose an algorithm with less computational complexity to achieve a suboptimal solution. Then, according to the obtained scheduling results, we present an iterative Karush-Kuhn-Tucker (KKT) method to solve the PA problem. Extensive simulations are conducted to verify the effectiveness and efficiency of the proposed algorithms. Two kinds of JP CoMP schemes are compared with a non-CoMP greedy scheme (max capacity scheme). Simulation results prove that the CoMP schemes with the proposed RRM algorithms dramatically enhance data rate of cell-edge UEs, thereby improving UEs' fairness of data rate. Also, it is shown that the proposed PA algorithms can decrease power consumption of transmission antennas without loss of transmission performance.

• JSTS:Journal of Semiconductor Technology and Science
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• 제14권6호
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• pp.802-809
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• 2014

This paper presents a dual-mode bias modulator (BM) for complementary metal oxide semiconductor (CMOS) power amplifiers (PAs). The BM includes a hybrid buck converter and a normal buck converter for an envelope tracking (ET) mode for high output power and for an average power tracking (APT) mode for low output power, respectively. The dual-mode BM and CMOS PA are designed using a $0.18-{\mu}m$ CMOS process for the 1.75 GHz band. For the 16-QAM LTE signal with a peak-to-average power ratio of 7.3 dB and a bandwidth of 5 MHz, the PA with the ET mode exhibited a poweradded efficiency (PAE) of 39.2%, an EVM of 4.8%, a gain of 19.0 dB, and an adjacent channel leakage power ratio of -30 dBc at an average output power of 22 dBm, while the stand-alone PA has a PAE of 8% lower at the same condition. The PA with APT mode has a PAE of 21.3%, which is an improvement of 13.4% from that of the stand-alone PA at an output power of 13 dBm.

• 한국전자통신학회논문지
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• 제7권1호
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• pp.135-139
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• 2012

LTE (long-term evolution) 를 비롯한 4G 이동통신 기지국 시스템에 있어서 최근에 DU(digital unit)와 RU(radio unit) 로 분리된 형상의 기지국들이 많이 등장하고 있다. 이러한 형태의 기지국에서 DU 는 전화국사에 설치하고 RU 는 옥외에 설치하는 형태로서, DU와 RU 간의 분리 가능한 거리는 이동통신 망 설계를 하는데 있어서 매우 중요한 요소가 된다. 하지만, DU와 RU 간 허용거리는 이동통신의 물리계층 기술에 의해 제약을 받을 수 있다. 본 논문에서는 FDD (frequency division duplexing) 기반의 4G 이동통신 시스템에서 Closed-Loop MIMO (multiple input multiple output) 기술에 의해 제한되는 DU와 RU 간 한계거리에 대해 분석하였다. DU와 RU 간 한계거리는 이동통신 시스템의 동작 주파수에 따라 다른 결과를 나타내며, 2 GHz의 동작주파수를 가정할 경우에는 약 11 km의 한계거리를 가지는 것으로 분석되었다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권9호
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• pp.2967-2981
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• 2014

Device-to-Device (D2D) communication is a technology component for long-term evolution-advanced (LTE-A). In D2D communication, users in close proximity to each other can communicate directly without going through a base station; such direct communication can improve spectral efficiency. Although D2D communication brings improvement in spectral efficiency, it also causes interference to the cellular network as a result of spectrum sharing. In particularly, D2D communication can generate interference for each D2D pair when the common wireless medium in a co-located limited area is accessed. Even though the interference management for between the D2D pair and cellular networks has been proposed, the interference reducing methods have still not been fully studied for the D2D pairs. In this paper, we investigate the problem of D2D pair coexistence in which interference is considered between D2D pairs. Using a signal to interference model for a target D2D pair, we provide an analysis of the aggregated throughput of a dense D2D network. For a target D2D pair, we assume that the desired signal and interference signals obey multipath fading and shadow fading. Through analysis, we demonstrate the effect of cluster size such as the number of D2D pairs and the size of the considered area on the network performance. The analytical results are compared with computer simulations. Our work can be used for a rough guideline for controlling the system throughput in a dense D2D network environment.

• 한국융합학회논문지
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• 제10권10호
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• pp.107-115
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• 2019

인적 및 물적 피해를 크게 초래하는 건설현장의 안전사고를 효과적으로 방지할 수 있는 시스템이 절실히 필요하다. 건설현장의 안전관리 시스템은 주로 대규모 건설현장 위주로 시범 운용되고 있으나, 중소규모의 현장에서 저비용으로 운용할 수 있는 안전관리 시스템은 많이 부족한 실정이다. 건설현장의 안전사고는 예상되는 위험 지역에 허가받지 않은 작업자가 접근하지 못하도록 사전 조치를 하면 효과적으로 방지할 수 있다. 본 연구에서는 소규모 건설현장에서 저비용으로 운용할 수 있는 사물인터넷 기반의 위험구역 경보 시스템을 개발하였다. 본 시스템은 지그비 기반의 비콘기술과 셀룰러 이동통신 기술 등을 활용하여 건설현장에서 추가적인 네트워크의 구축이 없이 허가된 작업자 또는 외부인이 위험구역에 접근시에 감지하고, 안전 관리자에게 위험 경보를 즉시 통보하여 적절한 안전조치를 취할 수 있다.

• Journal of Internet Technology
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• 제21권1호
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• pp.249-264
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• 2020

Cellular (C) setups facilitate the connectivity amongst the devices with better provisioning of services to its users. Vehicular networks are one of the representative setups that aim at expanding their functionalities by using the available cellular systems like Long Term Evolution (LTE)-based Evolved Universal Terrestrial Radio Access Network (E-UTRAN) as well as the upcoming Fifth Generation (5G)-based functional architecture. The vehicular networks include Vehicle to Vehicle (V2V), Vehicle to Infrastructure (V2I), Vehicle to Pedestrian (V2P) and Vehicle to Network (V2N), all of which are referred to as Vehicle to Everything (V2X). 5G has dominated the vehicular network and most of the upcoming research is motivated towards the fully functional utilization of 5G-V2X. Despite that, credential management and edge-initiated security are yet to be resolved under 5G-V2X. To further understand the issue, this paper presents security management as a principle of sustainability and key-management. The performance tradeoff is evaluated with the key-updates required to maintain a secure connection between the vehicles and the 5G-terminals. The proposed approach aims at the utilization of high-speed mmWave-based backhaul for enhancing the security operations between the core and the sub-divided functions at the edge of the network through a dual security management framework. The evaluations are conducted using numerical simulations, which help to understand the impact on the sustainability of connections as well as identification of the fail-safe points for secure and fast operations. Furthermore, the evaluations help to follow the multiple tradeoffs of security and performance based on the metrics like mandatory key updates, the range of operations and the probability of connectivity.

• 한국산학기술학회논문지
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• 제12권5호
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• pp.2241-2248
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• 2011

본 논문에서는 고출력 및 고효율 특성을 지니는 질화갈륨(gallium nitride, GaN) 고출력 트랜지스터 소자를 이용하여 WiMAX 및 LTE(long term evolution) 시스템에 사용 가능한 60watt급 고출력증폭기 모듈을 팔렛트(palette) 타입으로 개발한 결과에 대하여 기술한다. 높은 이득을 얻기 위한 라인업(lineup) 구성을 위해 저전력이면서 고이득을 지니는 전치증폭단, 8watt급의 GaN 구동증폭단, 그리고 30watt급 GaN 소자 2개를 도허티(doherty) 구조로 구성한 60watt 고출력증폭단을 사용하였으며, 이로부터 2.5~2.68GHz에서 61.4dB의 이득과 ${\pm}$0.075dB의 우수한 이득 평탄도를 얻었다. 특히 구동단과 고출력증폭단은 고효율 및 고출력 특성의 GaN 소자를 사용하였고, 또한 추가적인 효율 개선을 위해 도허티 구조를 적용함으로써 보다 높은 효율을 가지도록 하였다. 현재 전 세계적으로 널리 사용되고 있는 WiMAX 신호를 사용하여 제작된 팔렛트 타입의 증폭기 모듈의 성능을 측정하였는데, RRH(remote radio head) 타입으로 구성된 사용 예에서 WiMAX 변조 신호 10watt 출력 기준으로 약 37~38%의 효율을 나타내었다. 제작된 증폭기 모듈을 디지털 전치왜곡기(digital predistorter, DPD)와 연동하여 시험한 결과 WiMAX 변조 신호 10watt 출력에서 ACLR은 46dBc 이상의 특성을 지닌다.