• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2010.07a
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• pp.96-97
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• 2010

다중 홉 중계기술은 차세대 무선통신을 위한 핵심 기술로 최근 전 세계적으로 활발히 연구되고 있으며, 셀 용량 증대, 셀영역 확장, 음영지역 축소 등의 장점으로 인하여, IEEE 802.11s, 802.15.4, 802.16j 등의 표준화에의 반영을 위한 논의가 활발히 진행되고 있다. 본 논문에서는 간섭신호가 존재하지 않는 이상적 네트워크 환경을 고려한 기존 연구의 한계를 극복하기 위해, 다중 간섭신호가 존재하는 레일레이(Rayleigh) 페이딩 채널에서 이중 홉(dual-hop) 복호후재전송(DF : decode-and-forward) 중계시스템의 시스템 모델을 제안하고, 모의실험을 통하여 불능확률 및 4진 직교 진폭 변조(4-QAM)를 위한 평균비트오율 (average bit error rate) 성능을 살펴본다.

• Annual Conference of KIPS
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• 2005.11a
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• pp.1319-1322
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• 2005

복호 후 전달 협력 통신 프로토콜(DFP: Decode-and-Forward Cooperative Communication Protocol)은 물리적인 안테나의 증가 없이 다중 안테나 시스템의 장점을 가지는 통신 방법이다. 지금까지는 신호 대 잡음 비율(SNR: Signal to Noise Ratio)이나 경로이득 크기의 루트를 취한 값들을 이용하여 중계 노드에서 복호한 데이터를 전달 여부를 결정하여 중계 노드에서 부정확한 검파가 되지 않도록 방지하였다. 본 논문에서는 기존의 DFP 에서 사용되던 SNR 을 대체할 수 있는 LLR(Log-Likelihood Ratio)를 이용하는 방법을 제안하였다. 레일리 페이딩 환경과 AWGN 환경에서 기준값이나 중계 노드의 위치에 상관없이 LLR 기반의 DFP 가 SNR 기반의 DFP 보다 높은 성능을 보이는 것을 확인하였다.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.8
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• pp.46-51
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• 2012

In this paper, we investigate the power allocation for cognitive relay networks. Cognitive relay networks offer not only increasing spectral efficiency by spectrum sharing but also extending the coverage through the use of relays. For spectrum sharing, conventional works have assumed that secondary users know perfect channel information between the secondary and primary users. However, this channel information may be outdated at the secondary user because of the time-varying properties or feedback latency from the primary user. This causes the violation for interference constraint, and the secondary user cannot share the spectrum of the primary after all. To overcome this problem, we propose the power allocation scheme for the secondary user under the allowable primary user's outage probability constraint. Since the proposed power allocation scheme does not use the instantaneous channel information, the secondary users have lower feedback burden. In addition, the proposed scheme is also robust to the outdated channel environment.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.12A
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• pp.1198-1206
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• 2010

Recently smart phone and tablet PC are regarded as the most valuable mobile devices, so the demand of customers for multimedia supporting has been greatly increased. The network operators are now considering the deployment of relay stations ensuring low installation costs for its service cell to improve the cell capacity. Enhancing the relay stations, however, increases intra-cell interference, which is affecting the quality of service and outage ratio. In this paper, we present MPFR(Multihop Partial Frequency reuse) as the new frequency reuse scheme to increase cell throughput while maintaining low outage ratio for the OFDMA cellular multihop networks. Dynamic power control is also introduced to improve cell capacity. Overall cell throughput and outage ratio are observed by the simulation, and comparison between MPFR and conventional multihop frequency reuse schemes is convincing the performance enhancement.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.4
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• pp.295-301
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• 2020

When a spacecraft in deep space falls into an abnormal state, an emergency communication channel between ground and the spacecraft is essential in order to perform analysis to the cause of the anomaly, and to remedy the spacecraft from the distressed state. Because the recovery actions generally comprises of long and complicated sequences of commands, the transmission of the recovery commands may require a reliable and a delay tolerant networking technology based on bundle routing. While the delay tolerant networking protocol becomes a prominent method interfacing ground and space into a internet-like Solar system network because it can address the issues of the severe communication problems in deep space, the communication system on the spacecraft which based on space packet protocol cannot use the delay tolerant networking technology directly. So a community of the consultative committee for space data systems starts a discussion of the first-hop last-hop mechanism to establish a feasible concept and standardization. This paper presents an enhanced concept of the first-hop last-hop by applying it a virtual cislunar communication environment, and we believe this contributes to make a way applicable to an interoperable relay concept of the first hop last hop between the delay tolerant networking and space packet protocol standard.

• Journal of KIISE:Information Networking
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• v.30 no.2
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• pp.252-259
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• 2003

In the case of link congestion, most of the existing ad-hoc routing protocols like AODV and DSR do not try to discover a new route if there is no change in the network topology. Hence, with low mobility, traffic may get concentrated on some specific nodes. Since mobile devices have low battery power and low computing capability, traffic concentration on a specific node is not a desirable phenomenon. Therefore, in this paper, we propose a new protocol called SLAP (Simple Load-balancing Ad-hoc routing Protocol) which resolves the traffic concentration problem by letting each node check its own load situation and give up its role as a packet forwarder gracefully in the case of high traffic load. We compare the performance of SLAP with that of AODV and DSR in terms of the forwarding traffic distribution.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2018.10a
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• pp.571-573
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• 2018

Wireless sensor networks have unbalanced energy consumption due to the convergence structure in which data is concentrated to sink nodes. To solve this problem, in the previous research, the relay node was placed between the source node and the sink node to merge the data before being concentrated to the sink node. However, selecting a relay node that does not consider the link quality causes packet loss according to the link quality of the reconfigured routing path. Therefore, in this paper, we propose a link cost calculation method for data reliability in routing path reconfiguration for relay node selection. We propose a link cost estimation formula considering the number of hops and RSSI as the routing metric value and select the RSSI threshold value through the packet transmission experiment between the sensor modules.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.4
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• pp.430-436
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• 2014

This paper relates to the study about the street security light management system. The purpose of the wireless remote management system is to manage street security lights efficiently. The system is composed of three components like light controller, CDMA gateway and web based remote management server. The zigbee solution is adopted to make local wireless network between street security lights. The CDMA network is used for the wireless communication between street security light controller and the remote control center. The gateway to interconnect zigbee network and CDMA was designed with low power 32 bits Cortex M3 micro-controller. For the data communication between the management server and the gateway, SMS and socket based TCP streaming is used. The management server sends SMS to the gateway to deliver light control and management requests, and the gateway replies with the light controllers report via TCP streaming. By using both SMS and TCP streaming communication, it was verified that simple cost effective management is possible for street security lights. We tried real test for 95 street security lights in real environment during two months and analyzed the practical possibility for mass supply.

• Journal of Convergence for Information Technology
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• v.9 no.3
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• pp.22-29
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• 2019

Due to the development of ICT technology, convergence reality contents are utilized as technology for providing services in various industrial fields by visualizing various information such as sensor information and shared information in a service platform showing only simple three-dimensional contents. Research is underway to reduce the weight of applications by transmitting the resources of the object to be enhanced to the network as the information and the contents to be provided increase. In order to provide resources through the network, servers for processing various information such as pattern information, content information, and sensor information must be constructed in a cloud environment. However, in order to authenticate data transmitted and received in real-time in a cloud environment, there is a problem in that the processing is delayed and a delay phenomenon occurs in the rendering process and QoS is lowered. In this paper, we propose a system to distribute cloud server which provides augmented contents of convergent reality service that provides various contents such as sensor information and three - dimensional model, and shorten the processing time of reliable data through distributed relay between servers Respectively.

• KIISE Transactions on Computing Practices
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• v.20 no.11
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• pp.598-603
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• 2014

In wireless sensor networks, two methods have been generally used to track continuously moving object: a user query-based method and a periodic report-based method. Although the former method generates more overhead as a result of the user queries, the former one is also an energy-efficient method that does not transfer unnecessary information. For the user query-based method, a virtual tree that consist of sensor nodes is used to perform the user query and the sensor reporting. The tree stores the information of the mobile objects, and the stored information triggers a report b the user query. However, in case of a fast-moving object, the tracking accuracy decreases as a result of the time delay of the end-to-end repeated query. In order to solve this problem, we propose a query-relay method that reduces the time delay for mobile object tracking. In the proposed method, the nodes in the tree relay the query to adjacent nodes according to the movement of mobile object that is tracked. When the query messages are relayed. The end-to-end querying time delay is reduced. and a simulation shows that our method is superior to existing ones in terms of tracking accuracy.