• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.10A
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• pp.1532-1538
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• 1999

In general, because error rate of wireless link is higher than that of wired link, DLC layer protocol for wired network with low error rate is not proper for wireless environments. In addition, the conventional DLC layer protocol for wireless network is optimized for the low-speed data service, so it is difficult to use conventional DLC protocol in the current mobile communication environments handing high-speed and multimedia services. Therefore, a DLC layer protocol that is suitable to current wireless communication environments is required. In this paper, we propose a novel error control scheme that supports a variety of traffic attribute and is applicable to high-speed and multimedia data service in WATM. The proposed scheme provides enhanced throughput performance for real-time traffic by using modified ASR ARQ without ACK and reduces loss rate by using FEC in the case of high error condition. Also, for non real-time traffic, the use of ASR ARQ without ACK enhances throughput performance and delay time is decreased by using FEC in the case of high error rate channel. As a result of simulation, the proposed scheme has better performance than conventional ASR ARQ protocol in view of delay and throughput.

• The Transactions of the Korea Information Processing Society
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• v.1 no.2
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• pp.244-253
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• 1994

Computer networks need a variety of services. Some services such as, video, voice and plantcontrol traffic require a real-time communication with explicit timing constraints. In this pater, we introduce a real-time communication technique which use a reservation technique on dualilnk networks. We introduce an enhanced technique that determines priorities of the message based on time constraints when real-time messages are transmitted. A simulation was conducted to compare and to analyze traditional technique. We used the SLAM II language to simulate this technique. Message loss rate were compared and analyzed as a performance criteria in this simulation.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.9
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• pp.1492-1512
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• 2011

Due to multiple hops, mobility and time-varying channel, supporting delay sensitive real-time traffic in wireless local area network-based (WLAN) mesh networks is a challenging task. In particular for real-time traffic subject to medium access control (MAC) layer control overhead, such as preamble, carrier sense waiting time and the random backoff period, the performance of real-time flows will be degraded greatly. In order to support real-time traffic, an efficient adaptive packet scheduling (APS) scheme is proposed, which aims to improve the system performance by guaranteeing inter-class, intra-class service differentiation and adaptively adjusting the packet length. APS classifies incoming packets by the IEEE 802.11e access class and then queued into a suitable buffer queue. APS employs strict priority service discipline for resource allocation among different service classes to achieve inter-class fairness. By estimating the received signal to interference plus noise ratio (SINR) per bit and current link condition, APS is able to calculate the optimized packet length with bi-dimensional markov MAC model to improve system performance. To achieve the fairness of intra-class, APS also takes maximum tolerable packet delay, transmission requests, and average allocation transmission into consideration to allocate transmission opportunity to the corresponding traffic. Detailed simulation results and comparison with IEEE 802.11e enhanced distributed channel access (EDCA) scheme show that the proposed APS scheme is able to effectively provide inter-class and intra-class differentiate services and improve QoS for real-time traffic in terms of throughput, end-to-end delay, packet loss rate and fairness.

• Journal of Korea Multimedia Society
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• v.17 no.2
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• pp.143-151
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• 2014

In images degraded by bad weather, edges representing object boundaries become weak and faint. In this paper we present an image enhancement method, which increases image visibility by making edges as clear as possible. First, we choose edge candidate regions by finding local maxima and minima in an image intensity field, and then build a histogram using image intensities of pixels located at the two sides of candidate edges. Second, we decompose this histogram into multiple modes, which are determined by local minima in the histogram. Once modes are computed, we find modes connected by edges in the image intensity field and build link chains of connected modes. Finally we choose the longest link chain of modes and make the distances between every connected modes as large as possible. The darkest mode and the brightest mode should be within the image intensity range. This stretch makes edges clear and increases image visibility. Experiments show that the proposed method real-time enhances images degraded by bad weather as good as well known time-consuming methods.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.48 no.3
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• pp.6-12
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• 2011

Electric vehicles and robots are real-time distributed control systems composed of multiple drive subsystems using micro controller units. Each control subsystem should be modular, compact, power saving, interoperable and fault tolerable in order to be incorporated into the networked real-time distributed control system. Under the networked real-time distributed control the synchronization problem can be occurred to the position and orientation tracking control due to the load variance, mismatch and time delay between the multiple drive subsystems. This paper suggests two types of position synchronization control of the single link manipulators. One of them is composed of cross controller, Kalman filter and disturbance observer, and the other uses the generation of target trajectories to minimize the gradient vector of the scalar function which is composed of the sum of square errors between the reference input vector and the output vectors. The availability of the proposed control schemes is shown through the control experiments.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.12B
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• pp.1677-1685
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• 2001

In this paper, we propose a call admission control scheme that can be performed within guaranteeing of required QoS(Quality of Services) in DS-CDMA(Direct Sequence-Code Division Multiple Access) reverse link. It has been performed rely on a physical channel numberonly and based on quality of received signal from MODEM(modulator/demodulator) part in established study. In other methods, the standard for services would have been set from statistical analysis of users\` location and using received power level in BTS(Base Transceiver Station). These ways bring about not only system loads but time delay or great differences from real environment. To solve these problems, we propose a call drop rate estimation algorithm for the purpose of call admission control based on measured value at LNA(Low Noise Amplifier) ports of BTS(Base Transceiver Station) in real time. This method proposed in this paper estimates a quality of offered service in real time, reduce system loads and shorten time delay which is needed to determine the standard for call admission control. But it requires a additional 17W complexity which can measure received signal power in BTS and estimate call drop rate.

• Journal of Korean Society of Transportation
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• v.13 no.4
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• pp.5-29
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• 1995

Advanced Traveler Inoformation Systems*ATIS) , as a subsystem of ITS influence the travel choices of dreivers by providing them with historical, real-time and predictive information to supprot travel decisions and consequently improves the speed and quality of travel. For thesuccessul accomplishment of ATIS, the time-dependent variations of traffic in a road network and travel times of vehicles during their journey must be predicted . The purpose of this study is to evaluate the past developments in the dynamic route choice models and to apply the instantaneous dynamic user optimal route choice model. recently formulated with flow propagation constraints by Ran, Boyce and LeBlanc, to the real transportation network of Seocho-Ku in Seoul. As input data for this application, the time-dependent travel rates are estimated and the link travel time function is derived. The modelis validated from three view points : the efficiency of model itself the ability to predict traffic volume and travel time on links, and the optimal traffic control.

• Geomechanics and Engineering
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• v.25 no.2
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• pp.135-142
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• 2021

This study provided a new research perspective for processing and analyzing AE data to evaluate rock failure. Cluster method and information entropy theory were introduced to investigate temporal and spatial correlation of acoustic emission (AE) events during the rock failure process. Laboratory experiments of granite subjected to compression were carried out, accompanied by real-time acoustic emission monitoring. The cumulative length and dip angle curves of single links were fitted by different distribution models and distribution functions of link length and directionality were determined. Spatial scale and directionality of AE event distribution, which are characterized by two parameters, i.e., spatial correlation length and spatial correlation directionality, were studied with the normalized applied stress. The entropies of link length and link directionality were also discussed. The results show that the distribution of accumulative link length and directionality obeys Weibull distribution. Spatial correlation length shows an upward trend preceding rock failure, while there are no remarkable upward or downward trends in spatial correlation directionality. There are obvious downward trends in entropies of link length and directionality. This research could enrich mathematical methods for processing AE data and facilitate the early-warning of rock failure-related geological disasters.

• The Journal of the Acoustical Society of Korea
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• v.19 no.1
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• pp.89-96
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• 2000

ABR service is defined by ATM Forum and ITU for the efficient use of link bandwidth, and 2-pass service policing is proposed for this service. 2-pass service policing is effective by the real-time measurement of the used bandwidth, and this scheme obtains multiplexing gam and control efficiently ABR traffic as dynamically allocating rate by residual bandwidth information. In this study, we propose the real-time bandwidth prediction scheme for ABR traffic control, as using dynamic rate allocation by available bandwidth information. This study can obtain the simple hardware structure by means of as predicting available bandwidth by the total link bandwidth and the sum of transmission rate on the backlogged state connections.

• ETRI Journal
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• v.33 no.3
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• pp.382-392
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• 2011

This paper proposes the streaming radio frequency identification (RFID) protocol to support robust data streaming in a passive communication, which is extended from the ISO18000-6 Type C RFID standard. By observing and modeling the unique bit error behavior through detailed analysis in this paper, we found that performance is significantly limited by inaccurate and unstable link frequencies as well as low SNR which are inevitable for passive devices. Based on the analysis, we propose a simple and efficient protocol to adaptively insert extra error control sequences in a packet for tolerating tough link condition while maximizing the throughput and preserving the minimal implementation cost. To evaluate effectiveness of our proposal in real-time streaming applications, we experimented on real-time H.264 video streaming and prototyped the system on FPGA. To our best knowledge, our paper is the first work to take analytical approach for maximizing the throughput and demonstrate the possibility of the realtime multimedia streaming transmission in the passive RFID system.