• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.11
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• pp.2604-2612
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• 1997

Media access control(MAC) protocol that is used between aircraft and ground station now is non-persistent CSMA protocol, but this protocol hs defects to apply in the wireless mobile radio communication environment. In this paper, to solve this Problems, the modified ICMA/CD protocol which ban be applied in the wireless environment was proposed and analyzed. In the modified ICMA/CD protocol, instead of usig special control channel, control signal was inserted into the uplink message. After the analysis, simulation was performed to approve the analysis resutls. As a results, modified ICMA/CD protocol can solve the hidden termined effect of CSMA protocol and packet detection delay time problem of ICMA/CD protocol and acquired the same channel throughput as CSMA/CD protocol. This results shows the modified ICMA/CD protocol can be used in the aeronauical telecommunication.

• Journal of Communications and Networks
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• v.11 no.2
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• pp.175-186
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• 2009

A new medium access control (MAC) scheme embedding physical channels into multiband carrier sense multiple access/collision avoidance (CSMA/CA) networks is proposed to provide strict quality of service (QoS) guarantee to high priority users. In the proposed scheme, two priority classes of users, primary and secondary users, are supported. For primary users physical channels are provided to ensure strict QoS, whereas secondary users are provided with best-effort service using CSMA/CA modified for multiband operation. The performance of the proposed MAC scheme is investigated using a new multiband CSMA/CA Markov chain model capturing the primary user activity and the operation of secondary users in multiple bands. The throughput of secondary users is obtained as a function of the primary user activity and other CSMA/CA parameters. It is shown that the new MAC scheme yields larger throughput than the conventional single-band CSMA/CA when both schemes use the same bandwidth.

• Journal of Advanced Navigation Technology
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• v.7 no.2
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• pp.199-205
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• 2003

In this paper, CSMA/CA protocol is modified for aeronautical VHF communication through collision alleviation and the change of retransmission slot selection method in flag used transmission. When collision occurred in the contention period of CSMA/CA process, it is generally waiting for retransmission delay and it has the double size of CW(Contention Window). To solve this problem, this paper modifies the change procedure of original contention window size and reduces the state transition in collision among the whole of it. Also, in this paper we reduces the second collision probability through the station has to enter Backoff mode with increased contention window in the first collision. In the result of simulation, it is verified that it has good property in throughput and delay, So the proposed protocol is suitable for aeronautical VHF communication.

• Journal of Communications and Networks
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• v.6 no.3
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• pp.226-234
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• 2004

This work presents a deterministic channel that rules according to inverse a power propagation law. The proposed channel model allows us to derive the lower bound and upper bound of packet's capture probability in Rayleigh fading and shadowing cellular mobile system. According to these capture probabilities, we analyze the system performance in the case of finite stations and finite communicated coverage of a base station. We also adopted a dynamic backoff window size to discuss the robustness of IEEE 802.11 draft standard. Some suggestions and conclusions from numerical results are given to establish the more strong CSMA/CA protocol.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.3 no.1
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• pp.75-82
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• 1999

This paper describes the implementation of wireless realtime monitoring system using modified CSMA/CA protocol. This system consists of wireless modem, central monitor, mobile station, DB server, and offer advantage of mobility, reduced installation time, long-term cost savings, and so on. And this system offers patient position pursuit service. Patient position pursuit service must be offered to deal with emergency which can be occured during patient movement. This paper proposes modified CSMA/CA protocol and patient position pursuit algorithm, implements wireless realtime monitoring system using it.

• Proceedings of the IEEK Conference
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• 2003.07a
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• pp.49-52
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• 2003

IEEE 802.11 MAC uses a distributed coordination function (DCF) known as carrier sense multiple access with collision avoidance (CSMA/CA) for medium access. Random back-off algorithm helps to avoid the collision. This paper proposes virtual back-off and modified back-off algorithm for reduce a waiting time by back-off and reduce the collision. The modified DCF is consisted of these two algorithms. We expect to reduce the average waiting time of each transmission by using the modified DCF algorithm.

• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.1032-1035
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• 1996

While Ethernet and TCP/IP are the most widely used protocol, for Real-time system, it is not applicable because it doesn't guarantee the deterministic transmission time. Furthermore, the TCP acknowledgement scheme and sliding window algorithm enforce to collide packets. Although various Collision-Free CSMA protocol was presented, it is very difficult to implement in well known OS(UNIX, WilidowsNT) because we have to modify network kernel. This paper presents another transmission protocol based on modified UDP. The colliding probability can be minimized by avoiding successive packet transmission and decreasing competition duration. The proposed algorithm can be used for the soft real-time industrial automation network.

• Journal of Internet Computing and Services
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• v.13 no.1
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• pp.7-14
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• 2012

In this paper, performance of IEEE 802.11 carrier-sense multiple access with collision-avoidance (CSMA/CA) protocols in saturated traffic conditions is presented taking into account the impact of imperfect channel sensing. The imperfect channel sensing includes both missed-detection and false alarm and their impact on the performance of IEEE 802.11 is analyzed and expressed as a closed form. To include the imperfect channel sensing at the physical layer, we modified the state transition probabilities of well-known two state Markov process model. Simulation results closely match the theoretical expressions confirming the effectiveness of the proposed model. Based on both theoretical and simulated results, the probability of detection is concluded as a dominant factor for the performance of IEEE 802.11.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.14 no.2
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• pp.83-88
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• 2000

A Development of a data logger for monitoring wasted water is introduced. A characteristics of the system with microcontroller are simple and cheaper. A portable RAM card is consisted for saving a monitored data. Serial communication is adopted to communicate with a remote monitoring computer. CSMA/CD, which is used widely as MAC(Medium Access Control) in ethernet, is modified to apply a RS485 serial communication. When the measured values run over a limit values, the data logger takes alarm.

• Proceedings of the IEEK Conference
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• 2003.11c
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• pp.191-194
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• 2003

In IEEE 802.11b, Medium Access Control Sublayer consists of DCF (Distributed Coordination Function) and PCF (Point Coordination Function). DCF provides contention based services and PCF provides contention free services for QoS satisfaction. DCF uses CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) as an access protocol. And PCF uses Polling Scheme. In this paper, a modified New-PCF, which gives weights to channels with heavier traffic load, was suggested. NS-2 simulations were conducted to compare the service performances with original DCF, PCF and the modified New-PCF respectively. Simulation results has shown the increased overall throughput with the proposed New-PCF compared with other cases.