• Journal of KIISE
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• v.43 no.8
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• pp.919-926
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• 2016

In a wireless network, TCP causes the performance degradation because of mistaking packet loss, which is caused by characteristics of wireless link and throughput oscillation due to change of devices connected on a limited bandwidth. Delay based TCP is not affected by packet loss because it controls window size by using the RTT. Therefore, it can solve the problem of unnecessary degradation of the rate caused by misunderstanding reason of packet loss. In this paper, we propose an algorithm for improving the remaining problems by using delay based TCP. The proposed scheme can change throughput adaptively by adding the RTT, which rapidly reflects the network conditions to BaseRTT. It changes the weight of RTT and the increases and decreases window size based on the remaining amount of the buffer. The simulation indicated that proposed scheme can alleviate the throughput oscillation problem, as compared to the legacy TCP Vegas.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.2
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• pp.53-59
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• 2009

In multi-user MIMO systems, a base station transmits multiple data to multi-user simultaneously in order to improve performance and bandwidth efficiency. When the base station transmits multiple data to multi-user simultaneously, multi-user interference occurs severely. In this paper, we define a post-processing leakage as the total power leaked from desired user to all other users after combining at the output of each user. Using concept of the post-processing leakage, we also define a performance metric, the so called signal-to-post-processing-leakage-plus-noise ratio (SPPLNR). Assuming that the receiver is the minimum mean square error (MMSE) receiver, we propose an iterative SPPLNR-based beamforming that determines beamforming vectors and combining vectors by using an iterative method. The proposed scheme does not impose a condition on the relation between the number of transmit antennas for the base station and the number of receive antennas for users. Simulation results show that the proposed scheme outperforms a beamforming scheme perfectly eliminating the multi-user interference when channel estimation error exists.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.7
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• pp.9-19
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• 2004

WLAN (Wireless Local Area Networks) needs error recovery and flow control schemes to support reliable multicast protocol. Limited wireless bandwidth, as well as queuing losses caused by the asymmetric wired/wireless interactions, demands more effective approaches for reducing packet losses. Moreover, since the wireless channel is a shared broadcast medium, if sender receives feedback information simultaneously from several receivers, the feedback delays data frame transmission of forward direction by introducing channel congestion and burden at the sender. Therefore, it is important to minimize the amount of feedback information from receivers. In this paper, we propose an ARS(Adaptive Redundancy Scheme) that combines FEC(Forward Error Correction) using channel state estimation and ARQ(Automatic Repeat Request) both to reduce the amount of feedback information and the number of retransmissions and to guarantee high data reliability in a WLAN multicast environment. Performance of the proposed scheme is evaluated by means of analysis and simulations in AWGN and Rayleigh fading channels. The results show that the proposed scheme reduces the amount of feedback information and the number of retransmissions and guarantees high data reliability, while keeping throughput efficiency similarly with the conventional FEC and ARQ scheme.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.12
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• pp.2323-2329
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• 2008

Advances in wireless communication and hardware technology have made it possible to manufacture high-performance tiny sensor nodes. More recently, the availability of inexpensive cameras modules that are able to capture multimedia data from the environment has fostered the development of Wireless Multimedia Sensor Networks(WMSNs). WMSN supplements the a advanced technique that senses, transmits, and processes the multimedia contents upon the text based traditional wireless sensor network. Since the amount of data which the multimedia contents have, is significantly larger than that of text based data, multimedia contents require lots of computing power and high network bandwidth. To process the multimedia contents on the wireless sensor node which has very limited computing power and energy, a technique for WMSN should take account of computing resource and efficient transmission. In the paper, we propose a new image compression technique YWCE for efficient compression and transmission of image data in WMSN. YWCE introduces 4 type of technique for motion estimation and compensation based on the Resolution Scalability of Wavelet. Experimental result shows that YWCE has high compression performance with different set of 4 type.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.5
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• pp.1325-1341
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• 1998

A conventional CBR channel is now capable of delivering several digitally compressed video programs due to recent advances in video compression, such as MPEG-2, and digital transmission technology. This paper presents a joint video coding scheme that is to maintain a constant sum of bit rates for all the programs but to allow the variable bit rate for individual program in the transimission environment mentioned above. Thus advantages of VBR video compression can be obtained. This paper contributes in two aspects. First, a rate-distortion estimation method for MPEG-2 video is proposed, which enavle us predict the amount of bits and the distortion generated from an encoded picture at a given quantization step size and vice versa. The most attractive features of the proposed rate-distortion estimation method are its accuracy and a computational complexity low enough to be applied to real-time video coding applications. Second, this paper presents an efficient and accurate joint rate control scheme using the rate-distortion estimation results and verifies its performance with experiments. The experimental results show that our coding scheme gives a significant gain even though a small number of video programs are coded jointly. For example, a stable picture quality is maintained among the video programs as well as within a program, and additional extra programs can be transmitted over the same channel bandwidth if the proposed joint video coding scheme is used.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.41 no.6
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• pp.209-220
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• 2004

The main feature of H.264 standard against conventional video standards is the high coding efficiency and the network friendliness. In spite of these outstanding features, it is not easy to implement H.264 codec as a real-time system due to its high requirement of memory bandwidth and intensive computation. Although the variable block size motion compensation using multiple reference frames is one of the key coding tools to bring about its main performance gain, it demands substantial computational complexity due to SAD (Sum of Absolute Difference) calculation among all possible combinations of coding modes to find the best motion vector. For speedup of motion estimation process, therefore, this paper proposes fast algorithms for both integer-pel and fractional-pel motion search. Since many conventional fast integer-pel motion estimation algorithms are not suitable for H.264 having variable motion block sizes, we propose the motion field adaptive search using the hierarchical block structure based on the diamond search applicable to variable motion block sizes. Besides, we also propose fast fractional-pel motion search using small diamond search centered by predictive motion vector based on statistical characteristic of motion vector.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.12
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• pp.22-31
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• 2015

Recently, 3rd Generation Partnership Project (3GPP) has developed device-to-device (D2D) communication to cope with the explosively increasing mobile data traffic. The D2D communication uses sidelink based on single carrier-frequency division multiple access (SC-FMDA) due to its low peak-to-average power ratio (PAPR). In addition, demodulation reference signal (DMRS) is designed to support multiple input multiple output (MIMO). In this paper, we propose the DFT-based channel estimation scheme for sidelink in D2D communication. The proposed scheme uses the 2-Dimensional Minimum Mean Square Error (2-D MMSE) interpolation scheme for the user moving at a high speed. We perform the system level simulation based on 20MHz bandwidth of 3GPP LTE-Advanced system. Simulation results show that the proposed channel estimation scheme can improve signal-to-interference-plus-noise ratio (SINR), throughput and spectral efficiency of conventional scheme.

• Journal of Korea Society of Industrial Information Systems
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• v.27 no.4
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• pp.19-27
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• 2022

In general, the performance of ML(Machine Learning) application is determined by various factors such as the type of ML model, the size of model (number of parameters), hyperparameters setting during the training, and training data. In particular, the recognition accuracy of ML may be deteriorated or experienced overfitting problem if the amount of dada used for training is insufficient. Existing studies focusing on image recognition have widely used open datasets for training and evaluating the proposed ML models. However, for specific applications where the sensor used, the target of recognition, and the recognition situation are different, it is necessary to build the dataset manually. In this case, the performance of ML largely depends on the quantity and quality of the data. In this paper, training data used for motion recognition application is augmented using the kernel density estimation algorithm which is a type of non-parametric estimation method. We then compare and analyze the recognition accuracy of a ML application by varying the number of original data, kernel types and augmentation rate used for data augmentation. Finally experimental results show that the recognition accuracy is improved by up to 14.31% when using the narrow bandwidth Tophat kernel.

• The Journal of the Acoustical Society of Korea
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• v.42 no.1
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• pp.25-31
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• 2023

In order to estimate the radial speed of an underwater object so-called target with active sonar, Continuous Wave (CW) pulse is generally used, but if a target is slow and at near distance, it is not easy to estimate the radial velocity of the target due to acoustic reverberation in the ocean. In 2017, Wang et al. utilized broadband signal of two Hyperbolic Frequency Modulation (HFM) pulses, which is known as a doppler-invariant pulse, with equal frequency band and in opposite sweep directions to overcome this problem and successfully estimate the radial speed of slow-moving nearby target. They demonstrated the estimation of the radial velocity with computer simulation using the parameters of two HFM starting time differences and receiving times. However, for it uses two HFM pulses with equal frequency, cross-correlation between the two pulses negatively affect the detection performance. To mitigate this cross-correlation effect, we suggest using two different band HFM with the opposite sweep directions. In this paper, a method of radial velocity estimation is derived and simulated using two HFM pulses with the pulse length of 1 second and bandwidth of 400 Hz. Applying the suggested method, the radial velocity was estimated with approximately 6 % of relative error in the simulation.

• The Transactions of the Korean Institute of Power Electronics
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• v.18 no.3
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• pp.225-231
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• 2013

This paper presents an improved signal processing technique in the square-wave-type voltage injection method for IPMSM sensorless drives. Since the sensorless method based on the square-wave voltage injection does not use low-pass filters to get an error signal for estimating rotor position and allows the frequency of the injected voltage signal to be high, the sensorless drive system may achieve an enhanced control bandwidth and reduced acoustic noise. However, this sensorless method still requires low-pass and band-pass filters to extract the fundamental component current and the injected frequency component current from the motor current, respectively. In this paper, these filters are replaced by simple arithmetic operations so that the time delay for estimating the rotor position can be effectively reduced to only one current sampling. Hence, the proposed technique can simplify its whole signal process for the IPMSM sensorless control using the square-wave-type voltage injection. The proposed technique is verified by the experiment on the 800W IPMSM drive system.