Vol. 44, No. 6,
Jun. 2017
Digital Library
A UAV Flight Control Algorithm for Improving Flight Safety
Suncheol Park, Sungrok Jung, Myungjin Chung
http://doi.org/10.5626/JOK.2017.44.6.559
A UAV(unmanned aerial vehicle) requires higher reliability for external effects such as electromagnetic interference because a UAV is operated by pre-designed programs that are not under human control. The design of a small UAV with a complete resistance against the external effects, however, is difficult because of its weight and size limitation. In this circumstance, a conventional small UAV dropped to the ground when an external effect caused the rebooting of the flight-control computer(FCC); therefore, this paper presents a novel algorithm for the improvement of the flight safety of a small UAV. The proposed algorithm consists of three steps. The first step comprises the calibration of the navigation equipment and validation of the calibrated data. The second step is the storage of the calibration data from the UAV take-off. The third step is the restoration of the calibration data when the UAV is in flight and FCC has been rebooted. The experiment results show that the flight-control system can be safely operated upon the rebooting of the FCC.
Multi-core Scalable Real-time Flash Storage Simulation
Hyeon-gyu Lee, Sang Lyul Min, Kanghee Kim
http://doi.org/10.5626/JOK.2017.44.6.566
As NAND flash storage is being widely used, its simulation methodologies have been studied in various aspects such as performance, reliability, and endurance. As a result, there have been advances in NAND flash storage simulation for both functional modeling and timing modeling. However, in addition to these advances, there is a need to drastically reduce the long simulation time that is required to evaluate the aging effect on flash storage. This paper proposes a so-called multi-core scalable real-time flash storage simulation method, which can control the simulation speed according to the user’s preference. According to this method, it is possible to speed up the simulation in proportion to the number of CPU cores arbitrarily given while guaranteeing the correctness of the simulation result. Using our simulator implemented in the form of the Linux kernel module, we demonstrate the multi-core scalability and correctness of the proposed method.
Grid Acceleration Structure for Efficiently Tracing the Secondary Rays in Dynamic Scenes on Mobile Platforms
Woong Seo, Byeongjun Choi, Insung Ihm
http://doi.org/10.5626/JOK.2017.44.6.573
Despite the recent remarkable advances in the computing power of mobile devices, the heat and battery problems still restrict their performances, particularly compared to PCs. Therefore, in the application of the ray-tracing technique for high-quality rendering, the consideration of a method that traces only the secondary rays while the effects of the primary rays are generated through rasterization-based OpenGL ES rendering is worthwhile. Given that most of the rendering time is for the secondary-ray processing in such a method, a new volume-grid technique for dynamic scenes that enhances the tracing performance of the secondary rays with a low coherence is proposed here. The proposed method attempts to model all of the possible spatial secondary rays in a fixed number of sampling rays, thereby alleviating the visitation problem regarding all of the cells along the ray in a uniform grid. Also, a hybrid rendering pipeline that speeds up the overall rendering performance by exploiting the mobile-device CPU and GPU is presented.
Korean Web Content Extraction using Tag Rank Position and Gradient Boosting
http://doi.org/10.5626/JOK.2017.44.6.581
For automatic web scraping, unnecessary components such as menus and advertisements need to be removed from web pages and main contents should be extracted automatically. A content block tends to be located in the middle of a web page. In particular, Korean web documents rarely include metadata and have a complex design; a suitable method of content extraction is therefore needed. Existing content extraction algorithms use the textual and structural features of content blocks because processing visual features requires heavy computation for rendering and image processing. In this paper, we propose a new content extraction method using the tag positions in HTML as a quasi-visual feature. In addition, we develop a tag rank position, a type of tag position not affected by text length, and show that gradient boosting with the tag rank position is a very accurate content extraction method. The result of this paper shows that the content extraction method can be used to collect high-quality text data automatically from various web pages.
Filter-Bank Based Regularized Common Spatial Pattern for Classification of Motor Imagery EEG
Sang-Hoon Park, Ha-Young Kim, David Lee, Sang-Goog Lee
http://doi.org/10.5626/JOK.2017.44.6.587
Recently, motor imagery electroencephalogram(EEG) based Brain-Computer Interface (BCI) systems have received a significant amount of attention in various fields, including medicine and engineering. The Common Spatial Pattern(CSP) algorithm is the most commonly-used method to extract the features from motor imagery EEG. However, the CSP algorithm has limited applicability in Small-Sample Setting(SSS) situations because these situations rely on a covariance matrix. In addition, large differences in performance depend on the frequency bands that are being used. To address these problems, 4-40Hz band EEG signals are divided using nine filter-banks and Regularized CSP(R-CSP) is applied to individual frequency bands. Then, the Mutual Information-Based Individual Feature(MIBIF) algorithm is applied to the features of R-CSP for selecting discriminative features. Thereafter, selected features are used as inputs of the classifier Least Square Support Vector Machine (LS-SVM). The proposed method yielded a classification accuracy of 87.5%, 100%, 63.78%, 82.14%, and 86.11% in five subjects(“aa”, “al”, “av”, “aw”, and “ay”, respectively) for BCI competition III dataset Iva by using 18 channels in the vicinity of the motor area of the cerebral cortex. The proposed method improved the mean classification accuracy by 16.21%, 10.77% and 3.32% compared to the CSP, R-CSP and FBCSP, respectively The proposed method shows a particularly excellent performance in the SSS situation.
A Test Scenario Generation Technique based on Task Information for Interaction Testing among Android Components
http://doi.org/10.5626/JOK.2017.44.6.595
Android applications are composed of one or more components. The components within an application or several applications may interact with each other primarily through intents. Such interactions may cause security and reliability issues such as broadcast theft, activity hijacking, and intent spoofing. These problems need to be resolved through testing techniques using various interaction test scenarios before an application gets launched. However, with the existing test scenario generation approach, some infeasible test scenarios may be generated since they do not consider the re-execution order based on activity setting when pressing the back button. This paper proposes a test case generation technique which removes infeasible interaction paths by utilizing the activity stack information.
Development of a Motor Speed Controller of Drones Considering Voltage Drop of Battery
Sunghee Lee, Bo Ram Yun, Deok Yeop Kim, Hwangsoo Kim, Woo Jin Lee
http://doi.org/10.5626/JOK.2017.44.6.601
Recently, we have frequently encountered flying drones with the growth of drone industry. However, it is difficult for a driver to stabilize the motor speed of drones, since the voltage of a Lithium polymer battery used in drones may suddenly drop or rise when its power is exhausted. The instability of the motor speed precludes the drone from maintaining a flight altitude, so that the fuselage of a drone performs ascending and descending repeatedly. For solving this problem, existing techniques either add a compensator considering voltage drop of battery or change the control model. Since these techniques use hardware-implemented modules or depend on motor type and experimental results, there is a problem that new suitable modules should be implemented in accordance with the used motor of the fuselage. For solving this problem, in this paper, we implement a motor speed controller in the firmware of drones by considering voltage drop of battery to enhance drone flight stability.
Water Level Forecasting based on Deep Learning : A Use Case of Trinity River-Texas-The United States
Quang-Khai Tran, Sa-kwang Song
http://doi.org/10.5626/JOK.2017.44.6.607
This paper presents an attempt to apply Deep Learning technology to solve the problem of forecasting floods in urban areas. We employ Recurrent Neural Networks (RNNs), which are suitable for analyzing time series data, to learn observed data of river water and to predict the water level. To test the model, we use water observation data of a station in the Trinity River, Texas, the U.S., with data from 2013 to 2015 for training and data in 2016 for testing. Input of the neural networks is a 16-record-length sequence of 15-minute-interval time-series data, and output is the predicted value of the water level at the next 30 minutes and 60 minutes. In the experiment, we compare three Deep Learning models including standard RNN, RNN trained with Back Propagation Through Time(RNN-BPTT), and Long Short-Term Memory (LSTM). The prediction quality of LSTM can obtain Nash Efficiency exceeding 0.98, while the standard RNN and RNN-BPTT also provide very high accuracy.
An Efficient MapReduce-based Skyline Query Processing Method with Two-level Grid Blocks
http://doi.org/10.5626/JOK.2017.44.6.613
Skyline queries are used extensively to solve various problems, such as in decision making, because they find data that meet a variety of user criteria. Recent research has focused on skyline queries by using the MapReduce framework for large database processing, mainly in terms of applying existing index structures to MapReduce. In a skyline, data closer to the origin dominate more area. However, the existing index structure does not reflect such characteristics of the skyline. In this paper, we propose a grid-block structure that groups grid cells to match the characteristics of a skyline, and a two-level grid-block structure that can be used even when there are no data close to the origin. We also propose an efficient skyline-query algorithm that uses the two-level grid-block structure.
An Effective Preference Model to Improve Top-N Recommendation
http://doi.org/10.5626/JOK.2017.44.6.621
Collaborative filtering is a technique that effectively recommends unrated items for users. Collaborative filtering is based on the similarity of the items evaluated by users. The existing top-N recommendation methods are based on pair-wise and list-wise preference models. However, these methods do not effectively represent the relative preference of items that are evaluated by users, and can not reflect the importance of each item. In this paper, we propose a new method to represent user"s latent preference by combining an existing preference model and the notion of inverse user frequency. The proposed method improves the accuracy of existing methods by up to two times.
Jitter-based Rate Control Scheme for Seamless HTTP Adaptive Streaming in Wireless Networks
Yunho Kim, Jiwoo Park, Kwangsue Chung
http://doi.org/10.5626/JOK.2017.44.6.628
HTTP adaptive streaming is a technique that improves the quality of experience by storing various quality videos on the server and requesting files of the appropriate quality based on network bandwidth. However, it is difficult to measure the actual bandwidth in wireless networks with frequent bandwidth changes and high loss rate. Frequent quality changes and playback interruptions due to bandwidth measurement errors degrade the quality of experience. We propose a technique to estimate the available bandwidth by measuring the jitter, which is the derivation of delay, on a packet basis and assigning a weight according to jitter. The proposed scheme reduces the number of quality changes and mitigates the buffer underflow by reflecting less bandwidth change when high jitter occurs due to rapid bandwidth change. The experimental results show that the proposed scheme improves the quality of experience by mitigating buffer underflow and reducing the number of quality changes in wireless networks.
The Analysis of Cipher Padding Problem for Message Recovery Security Function of Honey Encryption
http://doi.org/10.5626/JOK.2017.44.6.637
Honey Encryption (HE) is a technique to overcome the weakness of a brute-force attack of the existing password-based encryption (PBE). By outputting a plausible plaintext even if the wrong key is entered, it provides message recovery security which an attacker can tolerate even if the attacker tries a brute-force attack against a small entropy secret key. However, application of a cipher that requires encryption padding to the HE present a bigger problem than the conventional PBE method. In this paper, we apply a typical block cipher (AES-128) and a stream cipher (A5 / 1) to verify the problem of padding through the analysis of the sentence frequency and we propose a safe operation method of the HE.
Graph-based Wi-Fi Radio Map Construction and Update Method
http://doi.org/10.5626/JOK.2017.44.6.643
Among Wi-Fi based indoor positioning systems, fingerprinting localization is the most common technique with high precision. However, construction of the initial radio map and the update process require considerable labor and time effort. To address this problem, we propose an efficient method that constructs the initial radio map at each vertex based on a graph. In addition, we introduce a method to update the radio map automatically by mapping signal data acquired from users to the reference point created on each edge. Since the proposed method collects signal data manually only at the vertex of the graph to build the initial radio map and updates it automatically, our proposed method can dramatically reduce labor and time effort, which are the disadvantages of the conventional fingerprinting method. In our experimental study, we show validity of our radio map update method by comparing with the actual reference point data. We also show that our proposed method is able to construct the radio map with an accuracy of about 3.5m by automatically updating the radio map.
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