Distributed Interference-aware Medium Access Control for IEEE 802.15.7 Visible Light Communications

Kim, Eui-Jik,Kwon, Jung-Hyok,Kim, Dongwan,Lim, Yongseok MYU K.K. 2018 Sensors and materials Vol.30 No.8

<P>In this paper, we present a distributed interference-aware medium access control (DI-MAC) for IEEE 802.15.7 visible light communications (VLCs), which improves the spatial efficiency of VLC devices deployed in specific service areas. The DI-MAC adaptively adjusts the backoff exponent (BE) of each VLC device by considering the number of adjacent VLC devices causing the interference, which are called VLC interferers. Therefore, it reduces interference between the VLC devices and unnecessary waiting time for channel access. To this end, the DI-MAC conducts VLC interferer discovery by using the IDs of VLC interferers obtained via hello messages from adjacent VLC devices and then performing a BE adaptation to determine the BE of each VLC device based on the number of VLC interferers. An experimental simulation was conducted to evaluate the performance of the DI-MAC, and the results show that the DI-MAC obtains a higher aggregate throughput performance than the existing IEEE 802.15.7 VLC.</P>

Land Cover Classification of Imagery from Landsat Operational Land Imager Based on Optimum Index Factor

Acharya, Tri Dev,Yang, In Tae,Lee, Dong Ha MYU K.K. 2018 Sensors and materials Vol.30 No.8

<P>With over four decades spent collecting spaceborne moderate-resolution imagery, Landsat represents the longest remote sensing mission in the world, and has had various applications. Land cover mapping is its heritage for research around the world. Landsat 8 continues the legacy of previous Landsat systems, with a new Operational Land Imager (OLI) sensor that has high spectral resolution and improved signal-to-noise ratio for better characterization of land cover. With improved quality, data size also increases. Hence, with limited research in adjusting data size, it is necessary to explore robust land cover classification techniques that produce accurate maps with more or fewer inputs. The Optimum Index Factor (OIF) is a statistic value that can be used to select the optimum combination of three bands in a satellite image that has the highest amount of information. In this study, we explore the land cover classification of OLI imagery based on OIF. Two test sites were selected around the hilly regions of Korea for OLI original composite, first-rank OIF composite, and OLI original with sum derivative of top-three OIF ranked composites. These three composites were classified with the well-known Spectral Angle Mapper (SAM) and Support Vector Machine (SVM) classifiers. The results were then analyzed and compared on the basis of producer accuracy, user accuracy, overall accuracy, and kappa coefficient. The result shows that the first-ranked OIF with a three-band composite shows a similar classification accuracy in SVM and slightly less in SAM, while the ten-band composite with OLI original bands and the sum derivative of the top-three OIF rank shows the same result or a small improvement in SVM classification. OIF-derivative composites can be useful in classification problems depending on whether the minimum amount of data for a similar result or more data to achieve higher accuracy is preferred.</P>

Novel and Live Tracing Methodology for Power Cables and Transformers Based on Power Line Carrier Signals

Byun, Heejung,Shon, Sugoog,Yang, Soomi MYU K.K. 2018 Sensors and materials Vol.30 No.8

<P>The three-phase, four-cable type of power distribution lines branch into multiple circuits from local pole-or pad-mounted transformers, which makes the topology of lines complicated. A challenging issue is how to trace cables and transformers in a complicated distribution system. The proposed idea is based on a power line carrier signal, which has certain propagation characteristics along the distribution system. This novel and live tracing methodology, called the synchronized client and server method, is introduced, designed, and implemented to trace cables and transformers in the distribution system. The most difficult part of cable tracing is to isolate the signals needed for tracking from a mixture of signals routed through transformers or loads and signals transmitted directly along a test line. The algorithms needed to isolate the signals have been developed and a zero crossing sensor module is designed to ensure that the remote client and server are in phase. Simulations have been carried out to verify the proposed system using a Simulink simulator. Experiments have been conducted to verify the theoretical concepts in a test bed and a commercial building. Finally, the theory has been proved at a resolution of 0.5 ms from comparisons between the simulations and the experiments.</P>

Review of High-resolution Retinal Prosthetic System for Vision Rehabilitation: Our Perspective Based on 18 Years of Research

Lee, Sangmin,Koo, Kyo-in,Ko, Hyoungho,Seo, Jong-Mo,Cho, Dong-il Dan MYU K.K. 2018 Sensors and materials Vol.30 No.7

<P>Retinal degenerative diseases result in a progressive degeneration of photoreceptors in the retina and eventually lead to complete blindness. Among the many approaches tested, electrical stimulation of the remaining retinal neurons has shown the most promising results for vision rehabilitation of the blind. However, to improve the performance of retinal prosthetic systems, the fabrication of a device with a large number of stimulation electrodes is essential. For the successful development of a high-resolution prosthetic device, it is necessary to conduct highly collaborative research on microelectrode arrays and stimulation circuits, as well as verification of this research in animal experiments. In this paper, the requirements for a high-resolution retinal prosthetic system are explained, and then research efforts from around the world including the strategies of our research group to make major breakthroughs in artificial retina research are reviewed in detail.</P>

Adaptive Priority-based Medium Access Control Protocol for IEEE 802.15.6 Wireless Body Sensor Networks

Kim, Eui-Jik,Kim, Ho-Young,Kim, Daehee,Kim, Dongwan MYU K.K. 2018 Sensors and materials Vol.30 No.8

<P>Concern about energy-efficient medium access control (MAC) protocols for wearable devices is increasing owing to support for healthcare services using wireless body sensor networks (WBSNs). The most popular energy-efficient MAC protocol for WBSNs is the IEEE 802.15.6 standard, which adopts carrier sensing multiple access with collision avoidance (CSMA/CA). The CSMA/CA mechanism of the IEEE 802.15.6 standard allows differentiated channel access by assigning a different size of contention window to the nodes, each of which has a different priority. However, the existing CSMA/CA of IEEE 802.15.6 still cannot guarantee successful data transmission in error-prone channels and congested network environments, which leads to wasted energy owing to data retransmission. In this paper, we propose an adaptive priority-based MAC (AP-MAC) protocol for IEEE 802.15.6 WBSNs, which utilizes transmission opportunities suitable for WBSNs. For this, data types are classified with predefined priorities with each data type having a different opportunity to access the channel. In addition, the priority of each classification is updated adaptively according to the update metrics channel state and congestion level. Simulation results show the enhanced performance of the AP-MAC protocol compared with that of the IEEE 802.15.6 standard.</P>

Web-based User Interface for Electrical Cell-substrate Impedance Sensing System

Park, Chan-Young,Lee, Mi-So,Kim, Yu-Seop,Song, Hye-Jeong,Kim, Jong-Dae MYU K.K. 2018 Sensors and materials Vol.30 No.10

<P>In this paper, we propose a compact electrical cell-substrate impedance sensing (ECIS) system and a user interface for control and monitoring over the Internet. Since the proposed system is much smaller than existing devices and does not need input/output (I/O) devices, it is easy to install and prevents inadvertent user interaction. The proposed system can increase the efficiency of biological testing devices such as ECIS systems that require long-term experiments at long intervals. The temporal impedance change is measured and recorded on the embedded computer in the proposed system, and the resulting data can be displayed and controlled over the Internet using a web-based graphical user interface (GUI). Bioengineers are currently using the proposed systems for cell culture experiments and are very satisfied with the ease of installation and the ability to observe the experimental situation anytime and anywhere.</P>

Internet-of-Things-based Electric Cell-substrate Impedance Sensing System

Park, Chan-Young,Lee, Mi-So,Kim, Yu-Seop,Song, Hye-Jeong,Kim, Jong-Dae MYU K.K. 2018 Sensors and materials Vol.30 No.7

<P>In this paper, we propose an electric cell-substrate impedance sensing system that can be accessed from the internet. The hardware specification was derived using numerical simulations and culture chamber impedance emulators, and the impedance calculation methods were compared. In addition, we propose server-type software to easily control and monitor the system from the internet. Experimental results show that it is advantageous to use an acquisition device of 50 mega samples per second or more and to calculate the impedance using a sine fitting method rather than the lock-in detection method that is generally used. During experiments, there was no problem accessing the proposed server from the outside with standard computing devices.</P>

Optimization of a Pre-impact Fall Detection Algorithm and Development of Hip Protection Airbag System

Ahn, Soonjae,Choi, Dagyeong,Kim, Jongman,Kim, Seongjung,Jeong, Youngjae,Jo, Min,Kim, Youngho MYU K.K. 2018 Sensors and materials Vol.30 No.8

<P>In this study, a pre-impact fall detection algorithm using a custom-made inertial sensor was optimized, and a spring-trigger airbag system was developed for preventing injuries from falls. Four different types of simulated falls were performed by 20 healthy volunteers (age 23.4 +/- 4.4 years), and six different daily activities were tested in 14 elderly subjects (age 71.8 +/- 4.0 years). An inertial sensor unit was used to measure acceleration, angular velocity, and vertical angle during all activities. Thresholds of 0.9 g acceleration, 47.3 degrees/s angular velocity, and 24.7 degrees vertical angle were determined on the basis of optimizing lead time and accuracy in pre-impact fall detection. A belt-type airbag system consisted of a polyurethane inner skin, an artificial leather outer shell, and a spring-trigger inflator. To evaluate the accuracy of the airbag system, 10 healthy adult males (age 28.5 +/- 2.7 years) wore the system and performed three sets of simulated falls. Fall detection was achieved 401.9 +/- 46.9 ms before impact on average, and the airbag inflated without fail during the falls (100% sensitivity). In all daily activities, no airbag inflation occurred (100% specificity).</P>

Knee Acoustic Emission Characteristics of the Healthy and the Patients with Osteoarthritis Using Piezoelectric Sensor

Choi, Dagyeong,Ahn, Soonjae,Ryu, Jeseong,Nagao, Mitsuo,Kim, Youngho MYU K.K. 2018 Sensors and materials Vol.30 No.8

<P>Osteoarthritis (OA) is one of the most common causes of disability in elderly individuals. Although X-rays, MRIs, and arthroscopy are widely used to examine OA, they do not provide dynamic information on activity-based joint integrity. In this study, acoustic emission (AE) in healthy individuals and OA patients was determined using piezoelectric sensors. Twenty normal subjects and fourteen OA patients were asked to perform weight-bearing (stand-to-sit) and non-weight-bearing (extension to flexion) exercises for 4 s each. Sensors were attached to the medial and lateral epicondyles of the tibia and the front of the patella. An AE event was defined as the threshold crossing based on AE signals. The results indicated that OA and healthy groups exhibited signals at a frequency range corresponding to approximately 100 Hz-10 kHz and less than 1 kHz, respectively. The OA group exhibited an amplitude of AE signals and a number of AE events that exceeded those of the healthy group (p < 0.05). AE signals from lesions exhibited a higher dB value and a larger number of AE events than those at other locations. However, most patients exhibited significant increases in AE signal characteristics at the front of the patella. The results of this study can be helpful in the early diagnosis or easy monitoring of knee OA in daily lives.</P>

Regional Density-aware Data Collection Using Unmanned Aerial Vehicle in Large-scale Wireless Sensor Networks

Kim, Eui-Jik,Choi, Hyo Hyun,Kwon, Jung-Hyok MYU K.K. 2018 Sensors and materials Vol.30 No.8

<P>This paper presents a regional density-aware data collection (RDDC) using unmanned aerial vehicles (UAVs) in large-scale wireless sensor networks (WSNs). The RDDC is designed to support fast data collection by adaptively adjusting the value of the minimum contention window (CWmin) of the sensor nodes depending on the regional node density of sensing fields. The operation of RDDC consists of the region-partitioning, node-scanning, and data-collecting phases. In the region-partitioning phase, the RDDC partitions the sensing field into multiple regions and assigns a region ID to each sensor node according to the region to which it belongs. In the node-scanning phase, the RDDC calculates the node density of each region. Finally, in the data-collecting phase, the RDDC assigns different CWmin values to each sensor node considering the regional node density of each region. The experimental simulation results show that the RDDC obtains higher aggregate throughput and shorter delay than the existing data collection method.</P>