• Journal of Satellite, Information and Communications
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• v.12 no.1
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• pp.125-131
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• 2017

In this paper, an efficient structure of device-to-device (D2D) synchronization preamble is proposed to meet the enhanced time and frequency synchronization requirements for D2D communication. D2D communication can be applied not only for the cellular communications, but also unmaned aerial vehicle communications and vehicle-to vehicle communication. The proposed preamble structure is transmitting signals at every odd subcarriers, and empty the other subcarriers to minimize the effect of inter-carrier interference. According to the simulation results, the proposed preamble structure provides improved time offset estimation performance, without degrading frequency offset estimation performance compared to the current LTE D2D preamble.

• Proceedings of the Korea Information Processing Society Conference
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• 2012.04a
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• pp.60-61
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• 2012

D2D는 단말 디바이스간의 중간의 매개체 없이 직접 연결을 통해서 메시지나 컨텐츠 등을 전송하는 시스템으로서 이의 개발에는 동시에 두개 이상의 단말을 연결하여 직접 통신을 수행하고 그 결과를 확인하는 테스팅 기능이 요구된다. 기존의 일반적인 테스팅 환경은 하나의 단말에서 구현되는 응용이나 서비스의 구현을 테스팅하는데 집중되어 있으나 본 연구에서는 다수개의 단말을 연결하여 테스트할 수 있는 간이 테스팅 프레임워크를 구축하고자 한다. 이를 위하여 간단한 테스트 스크립트 엔진을 설계하였고 테스트 스크립트 상에 개별 디바이스를 지정할 수 있는 항목을 추가하여 디바이스 간의 동작을 명세할 수 있도록 하였다.

• Information and Communications Magazine
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• v.30 no.6
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• pp.26-32
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• 2013

Wi-Fi Direct는 Wi-Fi Alliance에서 인증한 Wi-Fi 기반기술로 AP (Access Point)나 라우터 같은 인프라장비 없이 단말 간에 직접 통신을 하는 프로토콜 방식을 의미한다. Wi-Fi Direct는 현재 스마트폰 뿐만 아니라 TV, 노트북, 프린터, 카메라와 같은 다양한 기기 등에 탑재되어 단말 간 직접 통신을 통하여 콘텐츠 및 서비스를 사용할 수 있는 기술이다. 본고에서 Wi-Fi Direct 기술을 동작 단계별로 구체적으로 살펴보고 새롭게 정의된 전력 절감 기술에 대해서도 살펴본다. 또한 Wi-Fi Direct 기반 응용 서비스를 알아본다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.2
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• pp.208-211
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• 2016

Device-to-Device communication(D2D) enables devices in proximity to communicate directly without going through the network infrastructure. In particular, D2D communications in a cellular network can improve the spectral efficiency by allowing the reuse of cellular resources. However, it is not easy to maintain the channel quality of the D2D links and to protect the cellular links from the D2D interferences, since the resource allocations for the cellular users will change with time due to the time-varying nature of the cellular channels. To mitigate the performance degradation of D2D links, we propose to exploit unlicensed bands as auxiliary resources when the D2D links share the uplink cellular resources. The effectiveness of the proposed scheme is verified through simulations.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.24 no.11
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• pp.1500-1506
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• 2020

In this paper, we study a scheduling problem based on reinforcement learning for overlay device-to-device (D2D) communication networks. Even though various technologies for D2D communication networks using Q-learning, which is one of reinforcement learning models, have been studied, Q-learning causes a tremendous complexity as the number of states and actions increases. In order to solve this problem, D2D communication technologies based on Deep Q Network (DQN) have been studied. In this paper, we thus design a DQN model by considering the characteristics of wireless communication systems, and propose a distributed scheduling scheme based on the DQN model that can reduce feedback and signaling overhead. The proposed model trains all parameters in a centralized manner, and transfers the final trained parameters to all mobiles. All mobiles individually determine their actions by using the transferred parameters. We analyze the performance of the proposed scheme by computer simulation and compare it with optimal scheme, opportunistic selection scheme and full transmission scheme.

• KIPS Transactions on Computer and Communication Systems
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• v.3 no.12
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• pp.455-462
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• 2014

In recent years, various services in mobile environments due to the growth of mobile devices and related techniques like wireless networks. Furthermore, as the increasing communication traffic in cellular networks has become a new significant issue, many studies for device-to-device(D2D) communication and D2D-based cooperative services have been performed recently. In this paper, we design a smart agent system for D2D-based cooperative services and propose a dynamic service binding method based on service ontology. We classify roles of mobile devices for cooperative services by defining three types of smart agents, and construct a knowledge base in order to describe properties of 'service' unit. The proposed knowledge model, D2D cooperative service ontology, can enable a autonomous cooperative services between mobile devices by binding a requested service to the appropriate member device according to the real-time context in mobile environments.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.10
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• pp.1986-1993
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• 2015

We investigate the optimal resource and power allocation for device-to-device (D2D) communications in a multicell environment. When D2D links reuse the cellular radio resources, each D2D user will interfere with a cellular link and other D2D links, in its own cell as well as in adjacent cells. Under such situation, we propose a coordinated resource allocation scheme that can handle the intercell interferences as well as the intracell interference. For a given resource allocation, we also formulate a power optimization problem and present an algorithm for finding the optimal solution. The resource and power allocation algorithms are designed to maximize the achievable rate of the D2D link, while limiting the generated interference to the cellular link. The performance of the proposed algorithms is evaluated through simulations in a multicell environment. Numerical results are presented to verify the coordination gain in the resource and power allocation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.2
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• pp.151-163
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• 2014

The recent wearable device's applications concentrates on providing diverse services such as location based service, context aware service to the users. These various services are implemented by the interactions between the wearable device and the user. In the legacy system, the interaction requires certain explicit configuration from the user. If the user is unfamiliar with the IT technology, it will be impossible to get the wanted service. Therefore, a new autonomous communication concept among neighbor devices is essential for people who is unfamiliar with the IT technology. The implicit human computer interface enables the user to acquire the services, even though the user don't know the IT technology. In this paper, we propose two BLE based protocols (B-LIDx protocol, B-PniP). B-LIDx protocol is the protocol for locationing the mobile device in indoor. B-PniP is a zero-configure opportunistic direct M2M communication protocol between neighbor devices to achieve the autonomous communication concept with zero-configuration. The protocol's evaluations are performed by measuring the time for finding the location of a mobile device in actual environment and aligning the time spent in services using the B-PniP.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.4
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• pp.229-239
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• 2013

Recently, device-to-device (D2D) communications have been highlighted to improve the spectral efficiency and offer various user experiences in cellular networks. In this paper, we survey standards and literatures related to the D2D technology and address various advantages of D2D technology, and the problems to be resolved before practically implemented. Especially, by considering an important interference issue between cellular and D2D links, five resource allocation and interference management scenarios are provided and their performances are evaluated through the system level simulations. The simulation results show that the use of D2D significantly improve the cell capacity and the D2D user rate due to the effects of frequency reuse and data off-loading. Notably, it is also shown that an optimal D2D communication range exists to maximize the system performance.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2015.05a
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• pp.126-129
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• 2015

Device-to-device (D2D) communications, a subset of Proximity-based Services that enables direct communication between LTE network subscribers, is gaining popularity. It is well underway to be adopted in cellular communication systems for pedestrian and connected-vehicles alike. In this paper, we briefly present our model of an Evolved Packet Core Network-assisted device discovery simulator and show the applicability of Proximity-based Services for Vehicular Ad-hoc Networks. Through the performance evaluation based on the developed simulation environment, it is shown that in case when users gather in the same vicinity, as in public transportation, LTE network data can be efficiently offloaded and multicasted through Wi-Fi for e.g. delivering traffic-related information and for the benefit of infotainment service consumers.