• The Journal of the Korea Contents Association
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• v.9 no.2
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• pp.36-42
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• 2009

In 2005, Chien and Chen proposed a remote user authentication scheme for preserving user anonymity to conquer some problems Das et. al. schemes have. In 2007, Hu et. al. pointed out that their scheme have some problems. Therefore, they proposed a new one and claimed that their scheme overcome all of these problems. However, We will show that Hu et. al. scheme still hold some problems; it cannot resist to denial of service attack and protect the user anonymity. Hence, we propose ours and demonstrate our scheme conquer these problems.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.9A
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• pp.762-771
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• 2005

In this paper, an efficient Adaptive quality-of-service (QoS) traffic control scheme with priority scheduling is proposed for the multimedia traffic transmission over wireless access networks. The objective of the proposed adaptive QoS control (AQC) scheme is to realize end-to-end QoS, to be scalable without the excess signaling process, and to adapt dynamically to the network traffic state according to traffic flow characteristics. Here, the reservation scheme can be used over the wireless access network in order to get the per-flow guarantees necessary for implementation of some kinds of multimedia applications. The AQC model is based on both differentiated service model with different lier hop behaviors and priority scheduling one. It consists of several various routers, access points, and bandwidth broker and adopts the IEEE 802.1 le wireless radio technique for wireless access interface. The AQC scheme includes queue management and packet scheduler to transmit class-based packets with different per hop behaviors (PHBs). Simulation results demonstrate effectiveness of the proposed AQC scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.10C
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• pp.635-640
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• 2011

This paper proposes a frequency offset estimation scheme with low-complexity for orthogonal frequency division multiplexing (OFDM)-based cognitive radio (CR) systems. The proposed scheme is applicable to any type of training symbol and has a lower complexity than the scheme in [9] by using the partial periodogram. Simulation results show that the estimation performance of the proposed scheme is almost the same as that of the scheme in [9].

• Journal of Institute of Control, Robotics and Systems
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• v.5 no.5
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• pp.540-549
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• 1999

In this paper, the vibration suppression scheme based on a model referece approach is proposed. The vibration results from the coupling of the system and its frequency are given by the mechanical factors. In the proposed scheme, a low frequency vibration mode is transferred to high one. And also its damping ratio can be increased without any mechanical redesign. Therefore, bandwidth and open loop gain of the plant are increased and the performance of the system can be improved. This paper analyzes the proposed vibration suppression scheme, which is compared with the conventional control scheme for mechanical resonance suppression. For proving the realistic validity, we apply the proposed scheme to a LOS(Line Of Sight) stabilization system which has vibration effect. Finally, the proposed scheme is verified through simulations and experiments.

• Journal of Industrial Technology
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• v.24 no.B
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• pp.177-186
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• 2004

The main bottleneck for a VOD system is bandwidth of storage or network I/O due to the high bandwidth requirements and long-lived nature of digital video. Patching is one of the most efficient techniques to overcome the bottleneck of the VOD system through the use of multicast scheme. In this paper, we propose a new patching scheme, P2P proxy patching, for improving the typical patching technique by jointly using the proxy prefix caching scheme and the P2P proxy. In our proposed scheme, each client play a role in a proxy for multicasting a regular stream to other clients that request the same stream. Due the use of the P2P proxy and the prefix caching, the server bandwidth is required significantly less than that of the typical patching technique. In the performance study, we show that our patching scheme can reduce the server bandwidth requirements compared with the existing patching techniques.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2004.10a
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• pp.19-26
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• 2004

This study constructs the reduced system by two-level condensation scheme. This scheme consists of two steps. First step selects the candidate area for the primary degrees of freedom by energy estimation in element level. In the second step, the primary degrees of freedom are selected by the sequential elimination scheme. The efficiency and reliability of this scheme is shown through the prediction of eigenvalues of a few numerical examples. Time integration in the reduced system can save the computing time effectively. The well-constructed reduced system can present the accurate behavior of the structure under arbitrary dynamic loads so much as the global system. Through the numerical example, the efficiency and reliability of the proposed scheme will be demonstrated.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.3
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• pp.1319-1335
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• 2017

This paper proposes an opportunistic reporting-based sensing-reporting-throughput optimization scheme that maximizes the spectral efficiency of secondary users (SUs) in cooperative cognitive radio networks with a soft combining rule. The performance of cooperative spectrum sensing depends on the sensing time, the reporting time of transmitting sensing results, and the fusion scheme. While longer sensing time and reporting time improve the sensing performance, this shortens the allowable data transmission time, which in turn degrades the spectral efficiency of SUs. The proposed scheme adopts an opportunistic reporting scheme to restrain the reporting overhead and it jointly controls the sensing-reporting overhead in order to increase the spectral efficiency of SUs. We show that there is a trade-off between the spectral efficiency of SUs and the overheads of cooperative spectrum sensing. The numerical results demonstrate that the proposed scheme significantly outperforms the conventional sensing-throughput optimization schemes when there are many SUs. Moreover, the numerical results show that the sensing-reporting time should be jointly optimized in order to maximize the spectral efficiency of SUs.

• Journal of The Institute of Information and Telecommunication Facilities Engineering
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• v.10 no.4
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• pp.135-142
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• 2011

This paper proposes a performance evaluation method for power consumption of set-top box (STB) stand-by mode transition schemes. A stand-by mode transition scheme characterizes the timing of mode transition. The timing of mode transition affects the duration of stand-by mode operation, and the power consumptions of STB as well. Recently a fast stand-by mode transition scheme (FMT) has been proposed based on user input for selecting the device to be connected to TV. In this paper, we evaluate power consumption of FMT and a conventional mode transition scheme. For the computation of the duration of stand-by mode operation, the user input events are modeled as Poisson process. Simulation results based on the modeling reveals that the proposed scheme is more effective in power saving than the conventional scheme by up to 30%.

• Journal of the Korea Institute of Military Science and Technology
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• v.17 no.3
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• pp.336-341
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• 2014

When using a higher-order modulation scheme, there are variations in bit-reliability depending on the bit position in a modulation symbol. Variations of bit-reliability in the codeword block lower the decoding performance. Also, the decoding performance increases as the sum of the bit-reliabilities in the codeword block increases. This paper presents a novel hybrid automatic repeat request scheme that increases the sum of the reliabilities of the transmitted bits by lowering the modulation order, and decreases the variations of bit-reliability in the codeword block by preferentially retransmitting bits with low reliability. The proposed scheme outperforms the constellation rearrangement scheme. Furthermore, the proposed scheme also provides a good solution in cases where the size of the retransmission block is smaller than the size of the initial transmission block.

• Journal of information and communication convergence engineering
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• v.10 no.2
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• pp.117-122
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• 2012

We propose a hybrid multiple access (HMA) for uplink orthogonal frequency division multiple access (OFDMA) systems, which combines two resource sharing schemes: a scheduling-based resource allocation (SBRA) scheme and a contentionbased resource allocation (CBRA) scheme. The SBRA scheme is appropriate for non-real time high data rate traffic, and, CBRA is appropriate for near-real time low/medium data rate traffic. Thus, the proposed HMA scheme supports various types of traffic. As a CBRA scheme, our proposed random frequency hopping (RFH)-OFDMA scheme was presented. Simulation results show that the proposed HMA yields the best performance among various resource allocation schemes for uplink OFDMA systems.