• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.10
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• pp.2389-2396
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• 2014

Spectrum handoff is the process of exchanging progressing data transmission from the current channel to another idle channel. The essential goal of spectrum handoff in CR(Cognitive Radio) networks is to perform consistent data transmission while sustaining performance of ongoing transmission of secondary users. This handoff procedure can cause additional latency that eventually affects on the performance of CR transmission. Channel prediction method is expected to avoid the disruption to primary users and to reduce the handoff latency. In this paper, adaptive channel prediction is proposed to cope with time-varying channel and an adaptive channel prediction based proactive handoff procedure is designed to enhance data transmission performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.9B
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• pp.1108-1116
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• 2011

The visible light communication system that transmits data by controlling light emission of LED and receives data through photo detecter is considered as one of the strong candidates of the next generation wireless communication systems. The visible light communication provides both lighting and wireless communication wherever the LED lamps are installed. Due to the feature of visible light communication system, the communication is possible within the area that LED light reaches, and the communication quality depends on the light intensity received at the receiver. In this paper, we analyze the effects of LED panel position and lighting angel on communication channel quality in visible light communication systems. Through computer simulations, we prove that position of LED panel and light angle have a great impact on illuminance and SNR of the visible light communication systems.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.2B
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• pp.334-344
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• 2010

Recently, due to the prevalence of various mobile devices and broadband wireless networks, a significant interests and demands for multimedia streaming services over the Internet have been increasing. However, it is difficult to transmit continuous multimedia stream when mobile terminals are moving. Therefore, in order to deploy mobile IPTV service in the broadband wireless network, efficient wireless resource utilization and seamless QoE (Quality of Experience) offers to the users are an important issue. In this paper, we propose a network based adaptive streaming scheme, called MARC (Mobile Adaptive Rate Control), which controls the quality of the video and rate of the video based on the status of the wireless channel. The proposed scheme uses awareness information of the wireless channel status and controls transmitting streaming video which is suitable for the wireless channel status and mobile station location, in order to provide a seamless video playback for mobile environment in addition to improving the quality of a streaming service. The proposed MARC scheme alleviates the discontinuity of video playback and allocates suitable client buffer in broadband wireless network. Simulation results demonstrate the effectiveness of our proposed scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.6B
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• pp.517-526
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• 2006

In order to achieve high capacity and reliable link quality in wireless communication, the significant efforts should be concentrated on mitigating interference between cells. To solve the interference problem, the newly introduced concept of a Distributed Wireless Communication System (DWCS) can provide the capability of joint control of the signals at multiple cells. This paper proposes a new concept of virtual cell: the Dual Virtual Cell (DVC), and also proposes DVC employment strategy based on DWCS network. The proposed system manages two kinds of virtual cell. One is the Active Virtual Cell which exists for user's actual data traffic and the other is the Candidate Virtual Cell which contains a set of candidate antennas to protect user's link quality from performance degradation or interruption. The proposed system constructs DVC by using antenna selection method. Also, for multi-user high-rate data transmission, the proposed system introduces multiple antenna technology to get a spatial and temporal diversity gam and exploits space-Time Trellis Codes known as STTC to increase a spectral efficiency.

• Journal of Broadcast Engineering
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• v.14 no.1
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• pp.44-58
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• 2009

To provide efficient video streaming service over a wireless networks, the rate adaptation scheme should be applied at the low layer and the quality adaptation scheme should be considered at the high layer. In this paper, we propose a new cross-layer design which includes rate adaptation scheme at the MAC/PHY layers and quality control at the application layer. Proposed rate adaptation scheme improves the wireless channel utilization by transmitting the consecutive frames and selects optimal transmission mode by calculating the goodputs for each transmission mode. Based on selected transmission mode, the rate adaptation scheme calculates the rate limits and informs that to the application layer. Then the video streaming application utilizes this rate limits to adjust the quality of the video stream. Through performance evaluations, we prove that our cross-layer design improves the quality of the wireless video streaming service by means of the proposed rate adaptation scheme.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.10
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• pp.58-65
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• 2016

This paper presents optimization techniques to reduce the processing time of the dehazing method and proposes an efficient dehazing method based on them. In the proposed techniques, the atmospheric light is estimated based on the distributed sorting of the dark channel pixels, so as to reduce the computations. The normalization process required in the transmission estimation is simplified by the assumption that the atmospheric light is monochromatic. In addition, the dark channel is modified into the median dark channel in order to eliminate the transmission refinement process while achieving a comparable dehazing quality. The proposed dehazing method based on the optimization techniques is presented and its performance is investigated by developing a prototype system. When compared to the previous method, the proposed dehazing method reduces the processing time by 65% while maintaining the dehazing quality.

• Journal of Advanced Navigation Technology
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• v.19 no.4
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• pp.318-322
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• 2015

In wireless communication networks, most of the prediction techniques are used for predicting the amount of resource required by user's calls for improving their demanding quality of service. However, we propose a channel allocation scheme based on predicting the resources of white spectrum holes for improving the QoS of rental user's spectrum handoff calls for cognitive radio networks in this paper. This method is supported by Wiener predictor to predict the amount of white spectrum holes of license user's free spectrum resources. We classify rental user's calls into initial calls and spectrum handoff calls, and some portion of predicted spectrum-hole resources is reserved for spectrum handoff calls' priority allocation. Simulations show that the performance of the proposed scheme outperforms in spectrum handoff call's dropping rate than an existing method without spectrum hole prediction(11% average improvement in 50% reservation).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.1B
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• pp.20-26
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• 2010

The downlink scheduling algorithm has a great impact on the performance of mobile telecommunication system. In proportional fairness (PF) scheduling algorithm, the resource is allocated proportionally to the quality of wireless channel. Thus, PF has difficulty in servicing the users having more downlink traffic. One can allocate the resource proportionally to the accumulated queue length. However, this leads to system throughput degradation since the users having low channel quality get more and more resource allocated due to accumulation property of queue. In this paper, we propose a new downlink scheduling algorithm, which extends PF algorithm by incorporating downlink traffic arrival rate. The proposed algorithm can effectively cope with users having more downlink traffic, and maintain high system throughput by eliminating accumulation effect in the algorithm. With computer simulations, it is verified that the proposed algorithm performs better than existing algorithms.

• Journal of Digital Policy
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• v.2 no.3
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• pp.1-7
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• 2023

In this paper, I proposes a method for performing single image super resolution by separating texture-spatial domains and then classifying features based on detailed information. In CNN (Convolutional Neural Network) based super resolution, the complex procedures and generation of redundant feature information in feature estimation process for enhancing details can lead to quality degradation in super resolution. The proposed method reduced procedural complexity and minimizes generation of redundant feature information by splitting input image into two channels: texture and spatial. In texture channel, a feature refinement process with step-wise skip connections is applied for detail restoration, while in spatial channel, a method is introduced to preserve the structural features of the image. Experimental results using proposed method demonstrate improved performance in terms of PSNR and SSIM evaluations compared to existing super resolution methods, confirmed the enhancement in quality.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.2
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• pp.24-31
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• 2000

The channel allocation strategy is very important in wireless multimedia networks since the mobility of users needs to be considered in addition to diversity of QoS requirements of multimedia traffic. A existing strategy to decrease the probability of handoff failure is guard channel method, which reserves channels at each base station for handoff calls. In this paper, we propose an efficient channel allocation strategy based on the prioritization of handoff calls used in the guard channel method. In the Proposed strategy guard channels are shared between non-real time and real time handoff calls. To decrease the probability of handoff failure, (when resources become scarce), the Call Admission Control takes some resources away from the active calls. The simulation results demonstrate that the Proposed strategy Provides higher channel utilization and lower probability of handoff failure than those of existing strategies.