• Proceedings of the Korean Information Science Society Conference
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• 2006.06d
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• pp.85-87
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• 2006

센서 네트워크에서의 네트워크 리프로그래밍은 무선 통신을 통해 센서 노드에서 수행되는 소프트웨어를 변경하는 것으로서, 이를 사용하면 센서 네트워크를 구성하는 수백 개 혹은 수천 개의 노드들의 소프트웨어를 효과적으로 변경시킬 수 있다. 현재 네트워크 리프로그래밍을 위해 XNP, MNP. MOAP, Deluge, Mate 및 Incremental 기법 등이 제안되어 왔지만 아직 만족할만한 방법은 찾아보기 힘든 실정이다. 본 논문에서는 멀티홉을 지원하는 Deluge에 Incremental 기법을 통합하여 효율적인 리프로그래밍 기법을 구현하였다. 제안된 기법은 TinyOS 1.1.14 버전에 구현되었으며, 이를 통해서 네트워크 리프로그래밍을 위해 요구되는 패킷의 수와 소요시간을 크게 단축시킬 수 있다. 또한 센서 노드에서 패킷 전송에 따른 전력소 모가 가장 큰 점을 고려할 때 본 연구에서 제안하는 방식을 사용하면 센서 노드의 전력소모량도 크게 감소시킬 수 있는 효과를 기대할 수 있다.

• Proceedings of the Korea Contents Association Conference
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• 2003.05a
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• pp.361-367
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• 2003

Ad-hoc network is a multi-hop wireless network formed by a collection of mobile nodes without the aid of any establish infrastructure and this network can provide an extremely flexible method for establishing communications for fire, safety, rescue operations, battle field or other fields requiring rapidly deployable communications with survivable, efficient dynamic networking. Recently new expended mechanism is proposed as Ad-hoc relay system, so guarantee of QoS for multimedia applications is needed more and more. In this paper, we propose ARM based QoS Distribution Monitoring Mechanism to provide Quality of Service guarantees to multimedia application with MANET.

• Journal of Communications and Networks
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• v.13 no.4
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• pp.306-312
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• 2011

In this paper, an efficient retransmission scheme using cooperation from neighboring nodes is investigated. In the cooperative retransmission scheme, an erroneous packet is retransmitted to the destination by cooperative nodes where distributed beamforming is used to accommodate multiple cooperating nodes. A Markov model is used to analyze throughput efficiency and average delay of the proposed retransmission scheme. It is shown that the analytical results are well matched with the simulated results and improved throughput and delay performance can be achieved as compared to the traditional retransmission scheme. The performance of the proposed cooperative retransmission is investigated in the multi-hop configuration via computer simulation. The transmit power for retransmission packet is also investigated and it can be significantly reduced by using a small feedback channel.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.6A
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• pp.538-546
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• 2010

This paper presents an overview of position-based routing algorithms. We analyze performances of routing algorithms such as Hybrid Opportunistic Forwarding (HOF), Opportunistic multi-hop routing (ExOR), Location based Geocasting and Forwarding (LGF), and Greedy Forwarding in nearest with forward Progress (GFP) routing algorithms to find the best one in terms of packet error rate and throughput efficiency over effects of fading and noise variance in wireless networks. The analyses in closed form expressions are confirmed by the simulation results, which fully agree to analysis results. Additionally, the simulation results indicate significant differences among algorithms when varying the average SNR or the number of relays.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.5C
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• pp.487-494
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• 2010

This paper presents an OFDM-based dual-hop multi-relay system with best relay selection maximizing the mutual information. For the system either with decode-and-forward (DF) relays or with amplify-and-forward (AF) relays, we derive a lower-bound on the outage probability and the diversity order achievable in frequency selective fading channels and provide the outage capacity from simulation. Performance evaluation shows that both DF and AF provide the same diversity order as in the lower-bound but DF of which the outage probability is much closer to the lower-bound provides a better outage capacity than AF. It is also observed that the SNR gain of DF over AF gets larger as either the number of resolvable multipaths or the number of relay candidates increases, which makes DF relaying more favorable to the OFDM-based multi-relay system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.2A
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• pp.165-173
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• 2010

WMN(Wireless Mesh Network) is an wireless backbone network technology that is an easily configurable network in the low cost compared to the wireless LAN(Local Area Network). Most of the previous researches have evaluated their algorithms by the simulations rather than by the implementation. There exist some implementation papers, however, they have the limitations of the flexibility on the link establishment and the link quality utilization. Consequently, the benefit of the WMN - configuration flexibility is degraded and the performance deterioration occurs in the multi-hop wireless environment. In this paper, we introduce a Linux-based link layer Wireless Mesh Routing System - WBMR. The design and implementation of WBMR provides the dynamic link establishment and the effective multi-channel usage. We have modified the ntroof the original WLAN operation for the dynamic link establishment, and the Linux bridge for the link layer routing. The result of performance evaluation verifies that our WBMR supports fast self-configuration and increases data transmission throughput compared to the other researches of the wireless multi-hop environment.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.2B
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• pp.170-177
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• 2009

In this paper, we propose the structures of the NBTC (Narrow-Beam Trisector Cell) and the WBTC(Wide-Beam Trisector Cell) in which directional antennas both at the base station and at the relay station are used. We analyze and compare total capacity of the both systems taking the co-channel interference into consideration for two channel models. Through analysis, we find the effect of LOS (Lind of Sight) path to the total capacity of NBTC structure and that of WBTC structure. Our work may be useful as a guideline to control the interference for the next generation mobile communication and WiBro systems using multi-hop relays.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.11
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• pp.5253-5270
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• 2016

With device-to-device (D2D) communications, an inactive user terminal can be utilized as a relay node to support multi-hop communication so that connective experience of the cell-edge user as well as the capacity of the whole system can be significantly improved. In this paper, we investigate the spectrum sharing for a cooperative relay assisted D2D communication underlying a cellular network. We formulate a joint relay selection and channel assignment problem to maximize the throughput of the system while guaranteeing the quality of service (QoS) requirements of cellular users (CUs) and D2D users (DUs). By exploiting coalition formation game theory, we propose two algorithms to solve the problem. The first algorithm is designed based on merge and split rules while the second one is developed based on single user's movement. Both of them are proved to be stable and convergent. Simulation results are presented to show the effectiveness of the proposed algorithms.

• KIPS Transactions on Computer and Communication Systems
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• v.8 no.8
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• pp.191-200
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• 2019

In an Ad-hoc network, a method of time synchronizing all the nodes in a network centering on one reference node can be used. A representative algorithm based on a reference node is Flooding Time Synchronization Protocol (FTSP). In the process of sending and receiving messages, predictable and unpredictable delays occur, which should be removed because it hinders accurate time synchronization. In multi-hop communications, hop delays occur when a packet traverses a number of hops. These hop delays significantly degrade the synchronization performance among nodes. Therefore, we need to find a method to reduce these hop delays and increase synchronization performance. In the FTSP scheme, hop delays can be greatly increased depending on the position of a reference node. In addition, in FTSP, a node with the smallest node ID is elected as a reference node, hence, the position of a reference node is actually arbitrarily determined. In this paper, we propose an optimal reference node election algorithm to reduce hop delays, and compare the performance of the proposed scheme with FTSP using the network simulator OPNET. In addition, we verify that the proposed scheme has an improved synchronization performance, which is robust to topology changes.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.3A
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• pp.290-296
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• 2007

We propose new routing scheme, Cooperative Diversity-based Routing (CDR) which utilizes the cooperative space diversity for power saving and performance enhancement of wireless ad-hoc networks. The improved performance is compared with Multi-hop Relay Routing (NRR) by analytical methods. When the required outage probability is $1\times10^{-3}$ at the destination node in ad-hoc networks with 7 nodes, we noticed that each node can save power consumption by 15.5 dB in average, by using our proposed CDR compared to MRR.