• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.7
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• pp.45-51
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• 2009

We have presented a routing mechanism that selects a route by considering channel statuses in order to fast transfer delay-sensitive data in WSNs (Wireless Sensor Networks). The existing methods for real-time data transfer select a path whose latency is the shortest or the number of hops is the smallest. An algorithm to select a real-time transfer path based on link error rates according to the characteristic of wireless medium was also suggested. However, the propagation delay and retransmission timeout affected by link error rates are shorter than channel assessment time and backoff time. Therefore, the mechanism proposed in this paper estimated the time spent in using a clear channel and sending out a packet, which is based on channel backoff rates. A source node comes to select a route with the shortest end-to-end delay as a fast transfer path for real-time traffic, and sends data along the path chosen. We found that this proposed mechanism improves the speed of event-to-sink data transfer by performing experiments under different link error and channel backoff rates.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.10 s.340
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• pp.39-50
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• 2005

In this paper, we propose a performance improving MAC algerian for the IEEE 802.11 DCF. WLAN based IEEE 802.11 uses two control methods called 'Distributed Coordination Function(UF)' and 'Point Coordination Function(PCF)'. The nF controls the Urnsmission based on carrier sense multiple access with collision detection(CSMA/CA), that decides a random backoff time with the range of contention window for each terminal. Normally, each terminal the CW double after collision, and reduces the CW to the minimum after successful transmission. This paper proposes an enhanced DCF algorithm that decreases the CW smoothly after successful transmission in order to reduce the collision Probability by utilizing the current status information of WLAN. We also analyze the throughput and delay performance for the unsaturated case mathematically. Simulation results show that our algorithm enhances the saturation throughput of WLAN. They also coincide well with the analytical results.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2011.05a
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• pp.796-798
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• 2011

The IEEE 802.11 MAC uses DCF for media access among the participating network nodes. But DCF alone is neither capable nor suitable for fulfilling the QoS requirements of realtime applications. There are many ways in which QoS is provided by modifying DCF based MAC. This paper proposes (m,k)-collision scheme which is based on IEEE 802.11 and (m,k)-firm scheme tries to improve DCF functionality. The proposed scheme uses different Contention Window according to the number of collision in the node. The simulation result shows that the proposed scheme helps improve the throughput of the DCF.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.1
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• pp.578-582
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• 2005

This paper describes MAC schemes for QoS enhancement taking into account the traffic characteristics and network states over IEEE 802.11 wireless networks. Our approach uses AR as a Backoff parameter and to slide IFS adaptively for increasing the medium utilization ratio and throughput, and providing fairness. In addition, we evaluate through simulations using NS-2 the performance of proposed MAC scheme and compare it with other MAC schemes.

• Journal of Korea Society of Digital Industry and Information Management
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• v.5 no.4
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• pp.117-126
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• 2009

The recent interest in sensor networks has led to a number of routing schemes that use the limited resources available at sensor nodes more efficiently. These schemes typically try to find the minimum energy path to optimize energy usage at a node. Some schemes, however, are prone to unbalance of the traffic and energy. To solve this problem, we propose a novel solution: a gradient-field approach which takes account of the minimum cost data delivery, energy consumption balancing, and traffic equalization. We also modify the backoff-based cost field setup algorithm to establish our gradient-field based sensor network and give the algorithm. Simulation results show that the overhead of routing establishment obtained by our algorithm is much less than the one obtained by Flooding. What's more, our approach guarantees the basic Quality of Service (QoS) without extra spending.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.32 no.3
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• pp.10-19
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• 2009

Wireless LAN systems have been widely implemented for supporting the wireless internet services especially in the hotspot areas such as hospitals, homes, conference rooms, and so on. Compared with wired LAN systems, wireless LAN systems have the advantages of the users' mobility support and low implementation and maintenance costs. IEEE 802.11 wireless LAN systems employ the backoff algorithm to avoid contentions among STAs when two or more STAs attempt to transmit their data frames simultaneously. The MAC efficiency can be improved if the CW values are adaptively changed according to the channel state of IEEE 802.11 wireless LANs. In this paper, a dynamic contention window control algorithm is proposed using the genetic algorithm to improve the MAC throughput of IEEE 802.11 wireless LANs.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.1
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• pp.561-564
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• 2005

This paper proposes an access control algorithm for guaranteeing fair packet transmissions in CDMA-based slotted ALOHA systems. In the proposed algorithm, the base station calculates the packet transmission and retransmission probabilities based on the offered loads and then broadcasts these probabilities to all mobile stations. Mobile stations, which have a packet to transmit, attempt to transmit a packet with the received probabilities. Simulation results show that the proposed algorithm can offer better system throughput and average delay than the conventional algorithm. Results also show that the proposed algorithm can guarantee a good fairness among all mobile stations regardless of the offered loads.

• Proceedings of the Korea Society of Information Technology Applications Conference
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• 2005.11a
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• pp.179-182
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• 2005

The Home Phoneline Networking Alliance (HomePNA) 2.0 technology can establish a home network using existing in-home phone lines, which provides a channel rate of 4 - 32 Mbps. HomePNA 2.0 Medium Access Control (MAC) protocol adopts an IEEE 802.3 Carrier Sense Multiple Access with Collision Detection (CSMA/CD) access method, a Quality of Service (QoS) algorithm, and a Distributed Fair Priority Queuing (DFPQ) collision resolution algorithm. In this paper, we analyze the HomePNA 2.0 MAC protocol and propose the architecture of HomePNA 2.0 MAC controller circuit. Then, we present the simulation result of each block included in the HomePNA 2.0 MAC controller.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2005.10a
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• pp.365-368
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• 2005

이동중인 단말에게 인터넷 서비스를 제공하고자 하는 WiBro 시스템은, 무선자원의 효율적인 사용을 위해서 전송할 데이터가 있는 단말들에게만 대역폭을 할당하는 demand-based 대역폭 할당 방식을 사용한다. 이때 여러 단말들이 동시에 데이터를 전송하고자할 경우 충돌이 발생하므로 이들의 전송순서를 정해주는 것이 필요하다. 기존의 WiBro 시스템에서는 binary exponential backoff algorithm 에 기초한 random access 기법을 사용하는데, 본 연구에서는 conflict resolution 기법에 기초한 새로운 random access 기법을 제안하고, 새로운 기법의 성능이 보다 우수함을 시뮬레이션을 통해 보였다.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.10 s.352
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• pp.79-89
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• 2006

TCP is the most widely used transport protocol in Internet applications that guarantees a reliable data transfer. But, in the wireless multi-hop networks, TCP performance is degraded because it is designed for wired networks. The main reasons of TCP performance degradation are contention for wireless medium at the MAC layer, hidden terminal problem, exposed terminal problem, packet losses in the link layer, unfairness problem, reordering problem caused by path disconnection, bandwidth waste caused by exponential backoff of retransmission timer due to node's mobility and so on. Specially, in the mobile ad-hoc networks, discrepancy between a station's transmission range and interference range produces hidden terminal problem that decreases TCP performance greatly by limiting simultaneous transmission at a time. In this paper, we propose a new MAC algorithm for mobile ad-hoc networks to solve the problem that a node can not transmit and just increase CW by hidden terminal. In the IEEE 802.11 MAC DCF, a node increases CW exponentially when it fails to transmit, but the proposed algorithm, changes CW adaptively according to the reason of failure so we get a TCP performance enhancement. We show by ns-2 simulation that the proposed algorithm enhances the TCP performance by fairly distributing the transmission opportunity to the failed nodes by hidden terminal problems.