• Journal of the Korean Institute of Telematics and Electronics S
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• v.34S no.9
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• pp.1-12
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• 1997

The performance of Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) protocol adopted as a draft standard of IEEE 802.11 wireless LAN, is analyzed by using mathematical method based on renewal theory. We introdude three kinds of CSMA/CA protocols basic, stop-and-wait and 4-Way handshake CSMA/CA with their mathematical analysis. First, a network of finite population is considered and then expand to infinite population. We model the CSMA/CA protocol as a hybrid protocol of 1-persistent CSMA and p-persistent CSMA protocol, and verify analaytical results by computer simulation. We have found that 4-Way Handshake CAMA/CA shows better performance than those of other two types of CSMA/CA in case of high traffic load.

• Proceedings of the IEEK Conference
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• 2003.11c
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• pp.117-120
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• 2003

PON (Passive Optical Network) is an emerging local subscriber access architecture that provides more bandwidth and services to subscriber than DSL (Digital Subscriber Line and HFC (Hybrid-Fiber Coaxial) network. A PON is a point-to-multipoint optical network with no active elements in the signals' path from source to destination. Advantages of using PON for a subscriber access network include large coverage area, reduced fiber deployment, multicast and broadcast capabilities, reduced cost of maintenance (due to devices being passive), and ease of upgrades to higher bit rate or additional wavelengths. PON uses WDM (Wavelength Division Multiplexing) technique that transmits the downstream and upstream data at each different wavelength. For transmitting the CATV (Community Antenna television) service through PON network, we give out additional wavelength. This study shows the available TPS (Triple play service) architecture using CATV overlay EPON (Ethernet PON) architecture and analyzes the effects of EPON-based CATV transmission by measuring the power loss fur each wavelength and the power range of the available analog wavelength and RF.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.3B
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• pp.456-463
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• 2000

Bidirectional cable TV networks using HFC(Hybrid Fiber Coaxial) networks need MAC (Medium access control) protocols to have efficient access in upstream channels. In this paper, we have studied and evaluated several contention resolution algorithms and mapping of higher layer traffic described in IEEE 802.14 and MCNS (Multimedial Cable Network System) MAC protocols with respect to IP, ABR and CBR traffic types. IEEE 802.14 MAC protocol demonstrates better performance for transmitting ATM cells while the MCNS MAC protocols for the IP traffic.

• The Transactions of the Korea Information Processing Society
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• v.6 no.7
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• pp.1909-1918
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• 1999

The terrestrial/satellite hybrid network may replace or supply the terrestrial network in some areas or certain applications. For example, it may play a major role in global B-ISDN or in certain areas where the deployment of optical cable is not feasible, especially at the early stage of implementing terrestrial B-ISDN. Furthermore, it can play an important role in the development of B-ISDN due to their features of flexible wide coverage, independent of ground distances and geographical constraints, multiple access and multipoint broadcast. Also, satellite have the capability to supply terrestrial B-ISDN/ATM with flexible links for access networks as well as trunk networks. This paper describes the design and verification of the interworking protocol between terrestrial B-ISDN뭉 satellite network. For the verification, the designed interworking protocol is modeled by Petri-net and the model is analyzed by reachability tree.

• Journal of Integrative Natural Science
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• v.4 no.3
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• pp.238-242
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• 2011

For any pattern matching based algorithm in WLAN environment, the characteristics of signal to noise ratio(SNR) to multiple access points(APs) are utilized to establish database in the training phase, and in the estimation phase, the actual two dimensional coordinates of mobile unit(MU) are estimated based on the comparison between the new recorded SNR and fingerprints stored in database. The system that uses the artificial neural network(ANN) falls in a local minima when it learns many nonlinear data, and its classification accuracy ratio becomes low. To make up for this risk, the SVM/ANN hybrid algorithm is proposed in this paper. The proposed algorithm is the method that ANN learns selectively after clustering the SNR data by SVM, then more improved performance estimation can be obtained than using ANN only and The proposed algorithm can make the higher classification accuracy by decreasing the nonlinearity of the massive data during the training procedure. Experimental results indicate that the proposed SVM/ANN hybrid algorithm generally outperforms ANN algorithm.

• Structural Engineering and Mechanics
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• v.60 no.2
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• pp.193-209
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• 2016

In this study, wave force tests were carried out for the four types of offshore support structures with scale factor 1:25 and wave forces to the support structure shapes were investigated. As the results of this study, it was found that, as the wave period increased at the normal wave condition, wave force decreased for the most cases. Extreme wave force was affected by the impact wave force. Impact wave force of this study significantly effect on Monopile and slightly on GBS and Hybrid type. Accordingly, Hybrid type indicated even lower wave force at the extreme and irregular wave conditions than the Monopile although Hybrid type indicated higher wave force at the normal wave condition of the regular wave because of the larger wave area of wave body. In respects of the structural design, since critical loading is extreme wave force, it should be contributed to improve structural safety of offshore support structure. However, since the impact wave force has nonlinearity and complication dependent on the support structure shape, wave height, wave period, and etc., more research is needed to access the impact wave force for other support structure shapes and wave conditions.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.6
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• pp.1435-1440
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• 2014

Nodes in WSNs must operate under limited energy resource. Controlling access to the channel in WSNs plays a key role in determining channel utilization and energy consumption. This paper introduces a priority-based time slot allocation protocol for hybrid TDMA/CSMA MAC in WSNs. This protocol combines both TDMA and CSMA techniques while introducing prioritization by (m,k)-firm constraint. The performance of this protocol is obtained through simulations for various number of nodes and show significant improvements in delay and packet delivery ratio compared to S-MAC.

• KIPS Transactions on Computer and Communication Systems
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• v.2 no.10
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• pp.437-444
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• 2013

Recently, there are several attempts to save temporal, spatial and paper resources through mobile teleconference. However, present application-based mobile solutions have limited access, and are occasionally not working because of its operating system dependency. In recent times, several researchers attempt to develop mobile teleconference systems that can operate in all operating systems. It is still required to install proprietary applications to sync screens in user device. In this paper, we propose a full duplex and real-time data mirroring technology based on hybrid web that allows syncing screens without application installation, and operates in all mobile devices.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.7A
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• pp.682-688
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• 2006

In this paper, a soft-decision method for initial PN code acquisition in pilot-channel aided Direct Sequence Code Division Multiple Access (DS-CDMA) systems is proposed in order to improve the acquisition performance. We apply this technique to the conventional hybrid search algorithm and analyze it in terms of mean code acquisition time. For the analysis, we present mathematical model of proposed algorithm and also perform the simulation under IMT-2000 channel models. Numerical results show that our proposed scheme outperforms the conventional one by 0.2 - 0.4 sec with respect to the mean code acquisition time because the soft decision technique can mitigate the possible decline in search performance caused by the use of a hard-decision technique.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.9B
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• pp.1616-1623
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• 1999

This paper describes error resilient coding scheme is added in WLL system and its application for robust low-bit rate still image transmission over power controlled W-CDA system Rayleigh fading channels. The baseline JPEG compressing methods are uses in image coding over wireless channel. The channel uses Reed-Solomon(RS) outer codes concatenated with convolutional inner codes, and truncated type I hybrid ARQ protocol based on the selective repeat strategy and the RS error detection capability. Simulation results are proved for the statistics of the frame-error bursts of the proposed system in comparison with conventional WLL system. it gains the 2 dB of the Eb/No in same BER.