Sunwoo Kim

EMI shielding intrinsically conducting polymer/PET textile composites

Intrinsically conducting polymer(ICP)/PET textile composites were prepared by chemical and electrochemical polymerization of ICP on a PET fabric in sequence. We investigated the effects of the chemical or electrochemical polymerization conditions on the properties of resulting composites such as electrical conductivity and electromagnetic interference shielding effectiveness (EMI SE). The ICP/PET composite prepared in this study was highly electrically conducting, showing 0.3 Ω-cm of the specific volume resistivity and about 35 dB of EMI SE over a wide frequency range.

Multihop range-free localization with approximate shortest path in anisotropic wireless sensor networks

This paper presents a multihop range-free localization algorithm that tolerates network anisotropy with a small number of anchors. A detoured path detection is proposed to detect if the shortest path between nodes is detoured from their direct path by measuring the deviation in the hop count between the direct and shortest paths. A novel distance estimation method is introduced to approximate the shortest path based on the path deviation and to estimate their distance by taking into account the extent of the detour of the approximate shortest path. Compared to other range-free algorithms, the proposed algorithm requires fewer anchors while achieving higher localization accuracy in anisotropic networks. We demonstrated its superiority over existing range-free localization algorithms through extensive computer simulations.

Dual-Band On-Body Repeater Antenna for In-on-On WBAN Applications

A dual-band on-body repeater antenna for in-on-on wireless body area network applications is proposed. The proposed antenna has a maximum radiation normal to the human-body surface for communication with implanted devices in the 5.8 GHz industrial, scientific, and medical (ISM) band. In addition, to transmit the biological information received from the implanted devices to other on-body devices, the proposed antenna was designed to have a monopole-like radiation pattern along the surface of the human body for communication in the 2.45 GHz ISM band. The antenna was fabricated, and its performance was measured by attaching it to a human-equivalent semisolid phantom. In addition, the human-body effect was studied to ensure antenna performance under an actual situation.

RAPS: Reliable Anchor Pair Selection for Range-Free Localization in Anisotropic Networks

This letter presents a range-free localization algorithm with reliable anchor pair selection (RAPS) for anisotropic networks. To mitigate the effects of different network anisotropy, the proposed RAPS algorithm selects reliable anchor pairs by measuring the average hop progresses. The distances to the reliable anchors are estimated based on the geometric approximation of the node location. Compared to existing algorithms, the RAPS algorithm enables higher localization accuracy with fewer anchors while having less communication overhead in anisotropic networks. The superiority of the proposed algorithm is validated over the recently developed algorithms through extensive computer simulations.

Effect of hydroquinone on electrochemical oxidation of polypyrrole

Polypyrrole(PPy) formed electrochemically lost the redox reactivity with repeated cycles. The reactivity was preserved greatly by adding 0.005M of hydroquinone in the system. The improved stability of PPy in redox reaction may be attributed to the stabilization of free radicals in the polaron structure by hydroquinone.

Range-free indoor positioning system using smartphone with bluetooth capability

This paper presents a range-free localization system using commercial smartphones with Bluetooth capabilities to investigate the feasibility of range-free localization for indoor positioning. In the range-free localization system, each smartphone periodically scans nearby Bluetooth enabled devices and sends the results to the localization server. The localization server collects the scanning results from smartphones for a short period and find their locations via range-free algorithms. We have developed an Android application for smartphones. In addition to the localization server, a monitoring unit has been developed to supervise the range-free localization system. The range-free localization system was tested in a real environment. The experimental results showed that 5 m accuracy is achievable via range-free localization.

Kalman filter-based indoor position tracking with self-calibration for RSS variation mitigation

This paper investigates the indoor position tracking problem under the variation of received signal strength (RSS) characteristic from the changes of device statuses and environmental factors. A novel indoor position tracking algorithm is introduced to provide reliable position estimates by integrating motion sensor-based positioning (i.e., dead-reckoning) and RSS-based fingerprinting positioning with Kalman filter. In the presence of the RSS variation, RSS-based fingerprinting positioning provides unreliable results due to different characteristics of RSS measurements in the offline and online phases, and the tracking performance is degraded. To mitigate the effect of the RSS variation, a recursive least square estimation-based self-calibration algorithm is proposed that estimates the RSS variation parameters and provides the mapping between the offline and online RSS measurements. By combining the Kalman filter-based tracking algorithm with the self-calibration, the proposed algorithm can achieve higher tracking accuracy even in severe RSS variation conditions. Through extensive computer simulations, we have shown that the proposed algorithm outperforms other position tracking algorithms without self-calibration.

Analysis of Absorption Loss by a Human Body in On-to-Off Body Communication at 2.45 GHz

This paper investigates the effect of absorption loss by a human body to the received signal strength with respect to on-body transmitting antenna positions in on-to-off wireless body area networks. This investigation is based on measurement results obtained from experiments performed on human bodies (male and female) using planar inverted-F antennas in an anechoic chamber. The total absorption loss by the human body is also presented through the SEMCAD-X simulations. Our investigation showed that the received signal strength becomes lower when the transmitting antenna is mounted at a specific position where more absorption loss is experienced. The statistical analyses of on-to-off body channel characteristics based on the measurement results are presented.

IMU-assisted nearest neighbor selection for real-time WiFi fingerprinting positioning

This paper presents a nearest neighbor selection algorithm for real-time WiFi fingerprinting positioning with the assist of inertial measurement unit (IMU) measurements. The WiFi fingerprinting positioning using received signal strength (RSS) measurements suffers from the RSS variation problem. Due to this problem, reference points that are irrelevant to the users position are selected, and the positioning accuracy decreases. To overcome the RSS variation problem, we propose an IMU-assisted nearest neighbor selection algorithm that filters out irrelevant reference points based on the position prediction with IMU measurements. The proposed algorithm was evaluated and compared with the conventional ii-nearest neighbors (KNN) selection and the IMU-based dead-reckoning positioning in a real indoor environment. The experimental results showed that the average positioning error of the proposed algorithm was 2.41 m, whereas those of the KNN-based fingerprinting algorithm and the IMU-based dead-reckoning positioning were 3.57 m and 15.27 m.

Experimental outage capacity analysis for off-body wireless body area network channel with transmit diversity

This paper investigates the diversity gains and outage capacities of wireless body area network (WBAN) channels with transmit diversity. The off-body channel in an anechoic chamber, with respect to various human movements and the position of the transmit antennas, are measured to evaluate the influence of the usual body movements on the performance of off-body WBAN systems. It has been demonstrated that transmit diversity exploiting two uncorrelated channels relieves the harmful effect of human movement on the channel conditions and achieves high diversity gains.