• Journal of Electrical Engineering and Technology
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• v.5 no.2
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• pp.179-190
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• 2010

This paper describes a new stochastic heuristic algorithm in engineering problem optimization especially in power system applications. An improved particle swarm optimization (PSO) called adaptive particle swarm optimization (APSO), mixed with simulated annealing (SA), is introduced and referred to as APSO-SA. This algorithm uses a novel PSO algorithm (APSO) to increase the convergence rate and incorporate the ability of SA to avoid being trapped in a local optimum. The APSO-SA algorithm efficiency is verified using some benchmark functions. This paper presents the application of APSO-SA to find the optimal location, type and size of flexible AC transmission system devices. Two types of FACTS devices, the thyristor controlled series capacitor (TCSC) and the static VAR compensator (SVC), are considered. The main objectives of the presented method are increasing the voltage stability index and over load factor, decreasing the cost of investment and total real power losses in the power system. In this regard, two cases are considered: single-type devices (same type of FACTS devices) and multi-type devices (combination of TCSC, SVC). Using the proposed method, the locations, type and sizes of FACTS devices are obtained to reach the optimal objective function. The APSO-SA is used to solve the above non.linear programming optimization problem for better accuracy and fast convergence and its results are compared with results of conventional PSO. The presented method expands the search space, improves performance and accelerates to the speed convergence, in comparison with the conventional PSO algorithm. The optimization results are compared with the standard PSO method. This comparison confirms the efficiency and validity of the proposed method. The proposed approach is examined and tested on IEEE 14 bus systems by MATLAB software. Numerical results demonstrate that the APSO-SA is fast and has a much lower computational cost.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.3
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• pp.727-734
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• 2014

Digital processing technologies are being studied in various areas of image compression, recognition and recovery. However, image deterioration still occurs due to the noises in the process of image acquisition, storage and transmission. Generally in the typical noises which are included in the images, there are Gaussian noise and the mixed noise where the Gaussian noise and impulse noise are overlapped and in order to remove these noises, various researches are being executed. In order to preserve the edge and effectively remove mixed noises, image recovery filter algorithm was suggested in this study which sets and processes the adaptive weight using the median values and average values after noise judgment. Additionally, existing methods were compared through simulations and PSNR(peak signal to noise ratio) was used as a judgment standard.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.2B
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• pp.76-81
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• 2008

LEACH (Low Energy Adaptive Clustering Hierarchy) has been proposed as a routing protocol with a hierarchical structure, in order to achieve the energy efficiency that is of primary importance in the wireless sensor networks. A wireless sensor network adopting LEACH is composed of a few clusters, each of which consists of member nodes that sense the data, and head nodes that deliver the collected data from member nodes to a sink node that is connected to a backbone network. A head node in a cluster allocates TDMA slots to its member nodes without taking into account whether they have data to transmit or not, thus resulting in inefficiency of energy usage of head node that remains in active mode during the entire round time. This motivates us to propose a scheme to improve the energy efficiency of LEACH, by assigning TDMA slots only to those member nodes who have data to send. As a result, the head node can remain sleep during the period of no data transmission from member nodes, leading to the substantial energy saving. By using the ns-2 simulator, we evaluate the performance of the proposed scheme in comparison with the original LEACH. Experimental results validate our scheme, showing a better performance than original LEACH in terms of the number of outliving nodes and the quantity of energy consumption as time evolves.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.8A
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• pp.787-793
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• 2008

3GPP evolved packet system (EPS) is an all-IP based system that supports various access networks such LTE, HSPA/HSPA+, and non-3GPP networks. Recently, the support of IP flows with packet level QoS profiles was added to the requirements of the EPS. This paper proposes an adaptive modulation and coding (AMC) scheme that supports the QoS of such IP flows in the 3G LTE access network of the EPS. Defining the retransmission as a critical factor for QoS, the proposed scheme applies different maximum packet error probability $P_{max}$ to each packet when selecting the AMC transmission mode. In determining $P_{max}$, the QoS constraints and NACK-to-ACK error as well as channel condition are considered, balancing two objectives: the satisfaction of the QoS and the maximization of spectral efficiency. The simulation results show that it is able to reduce both delay violation and status report by 10%, while improving the throughput 10% in comparison with an existing scheme.

• Journal of Broadcast Engineering
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• v.17 no.1
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• pp.95-107
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• 2012

Network coding was proposed to increase the achievable throughput of multicast in a network. Recently, combining network coding into user cooperation has attracted research attention. For cooperative transmission schemes with network coding, users combine their own and their partners messages by network coding. In previous works, it was shown that adaptive DF with network coding can achieve diversity gain and additional throughput gain. In this paper, to improve performance of conventional protocols and maximize advantage of using network coding, we propose a new network coding based user cooperation scheme which uses adaptively amplify-and-forward and decode-and-forward according to interuser channel status. We derive outage probability bound of proposed scheme and prove that it has full diversity order in the high SNR regime. Moreover, based on the outage bound, we compute optimal power allocation for the proposed scheme.

• Journal of Satellite, Information and Communications
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• v.7 no.1
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• pp.65-74
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• 2012

The QoS guarantee for the forward link in satellite communication networks is very important because there are a variety of packets with multiplexing. Especially, the packets are processed depending on the available bandwidth in satellite network changing the wireless channel state in accordance with weather condition. The DVB-S2 increases the transmission efficiency by applying the adaptive coding and modulation (ACM) techniques as a countermeasure of rain attenuations. However, the channel estimation algorithm is required to support the ACM techniques that select the MODCOD values depending on the feedback data transmitted by RCSTs(Return Channel via Satellite Terminal) because satellite communication networks have a long propagation delay. In this paper, we proposed the channel estimation algorithm using rain attenuation values and reference data and the packet scheduling scheme to support the QoS and fairness. As a result of performance evaluation, we showed that proposed algorithm exactly predicts the channel conditions and supports bandwidth fairness to the individual RCST and guarantees QoS for user traffics.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.1
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• pp.237-243
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• 2015

In recent image processing, active researches have been made along with rapid development in digital times. However, it is know that the image degradation occurs due to various external factors in the processes of image data processing, transmission and storage, and the main reason of image degradation is due to the noise. Typical methods to remove the noise are CWMF(center weighted median filter), A-TMF(alpha-trimmed mean filter) and AWMF(adaptive weighted median filter) and these methods have a little bit lacking noise reduction characteristics in mixed noise environments. Therefore, in order to remove the mixed noise, image restoration filter processing algorithm was suggested in this paper which processes by applying the median value of the mask and space weighted value after noise judgment. And for the objective judgment, it was compared with existing methods and PSNR(peak signal to noise ratio) was used as a judgment standard.

• The KIPS Transactions:PartA
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• v.16A no.5
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• pp.327-338
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• 2009

Recently, with the advance of computing and networking technique, the high speed internet becomes widespread, however, it is still hard job to do streaming the media which requires high network bandwidth over the internet. Previous researches for streaming over the internet mainly proposed techniques that controls the QoS(Quality of Service) of the media in proportion to the network status. Though, this could be the solution for the service provider while the service user who wants constant QoS may not satisfy with variable QoS. In the paper, we propose a network adaptive prefetching technique, PAP, for guarantee of constant QoS. The PAP prefetches frames by increasing the frame transmission rate while the available network bandwidth is high. The PAP uses the prefetched frames to guarantee the QoS while the available network bandwidth is low and increases the playout interval to prevent buffer underflow. The experiment result shows that the proposed PAP could guarantee the constant QoS by prefetching the frames adaptively to the network bandwidth with the characteristic of video stream.

• Journal of Internet Computing and Services
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• v.17 no.6
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• pp.9-15
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• 2016

In this paper, we propose a smart HLS(HTTP Live Stream) platform with dynamic single buffering for the best transmission of adaptive video bit-rates. This smart HLS can optimizes the channel transition zapping-time with the monitoring of bandwidth between HLS server and OTT(Over The Top) client. This platform is designed through the control of video stream due to proper multi-bitrates and bandwidths. This proposed OTT can decode the live and VOD(Video On Demand) videos with the buffering of optimumal bitrate. And, the HLS can be cooperated with a smart OTT, and segmented for the m3u8 files of H.265 MPEG-2 TS(Transport Stream) videos. As a resullt, this single buffer based smart OTT can transmit optimal videos with the maximum data buffering according to the adaptive bit-rate depending on the network bandwidth efficiency and the decoded VOD video, too.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.1
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• pp.164-171
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• 2008

Adaptive equalizers are inevitable schemes in digital communication systems for compensating the transmission channel distortion. Additionally, to obtain the required BER(Bit Error Rate), the adaptive algorithms appropriate to the mobile communication channels are required. In this paper, we propose the NPDFE (Noise-Predictive Decision Feedback Equalizer) for communication systems performance improvement in mobile communication channels. The performance of the proposed NPDFE with QPSK (Quadrature Phase Shift Keying) is simulated under AWGN (Additive White Gaussian Noise), Ricean fading, ETSI (European Telecommunications Standards Institute) fading, and Rayleigh fading channels. The equalizers used in simulations are a LE (Linear Equalizer), a DFE (Decision Feedback Equalizer), and a NPDFE. Moreover, the equalizer performance criterion of the QPSK is the BER.