Nammoon Kim

Various Quantum- and Nano-Structures by III–V Droplet Epitaxy on GaAs Substrates

We report on various self-assembled In(Ga)As nanostructures by droplet epitaxy on GaAs substrates using molecular beam epitaxy. Depending on the growth condition and index of surfaces, various nanostructures can be fabricated: quantum dots (QDs), ring-like and holed-triangular nanostructures. At near room temperatures, by limiting surface diffusion of adatoms, the size of In droplets suitable for quantum confinement can be fabricated and thus InAs QDs are demonstrated on GaAs (100) surface. On the other hand, at relatively higher substrate temperatures, by enhancing the surface migrations of In adatoms, super lower density of InGaAs ring-shaped nanostructures can be fabricated on GaAs (100). Under an identical growth condition, holed-triangular InGaAs nanostructures can be fabricated on GaAs type-A surfaces, while ring-shaped nanostructures are formed on GaAs (100). The formation mechanism of various nanostructures can be understood in terms of intermixing, surface diffusion, and surface reconstruction.

A Passive Indoor Tracking Scheme With Geometrical Formulation

Passive tracking that aims to track targets without assistant devices, i.e., device-free targets, is addressed as an emerging field recently. This letter proposes a novel passive tracking algorithm with several pairs of position-known wireless terminals (WTs) and access points (APs), which can be implemented in wireless local area network environments. In the proposed scheme, we formulate the crossing point estimation on the line-of-sight paths (LOSPs) between APs and WTs of third parties, which reveal trajectory of the device-free target, as a geometrical optimization problem. Then, the optimization problem is solved by the particle swarm optimization algorithm. As essential knowledge, we first explore the characteristics of the wireless propagation radio frequency tomography, under LOSP. The tracking performance of the proposed scheme is evaluated via computer simulations as well as experiments in a (5 × 12)-m2 monitored area. The experimental results show that the proposed scheme can provide remarkable tracking accuracy of as high as decimeters.

An Adaptive AP Selection Scheme Based on RSS for Enhancing Positioning Accuracy

In recent years, the indoor positioning technologies have been recognized as core technologies for realizing smart space, a ubiquitous society, context awareness, and various location-based services. There are several approaches for positioning with radio signals, but the received signal strength (RSS)-based technology is considered a promising scheme because of its simplicity and practicality in implementation. In this paper, the positioning performance of the RSS value-based scheme is analyzed with respect to the location of access points (APs) and the number of APs in an indoor environment. An adaptive AP selection scheme and a base AP changing scheme are then proposed to enhance the positioning accuracy. In order to estimate the RSS characteristics, RSS values are measured as the distance between the AP and the receiver increases. The positioning performance is evaluated with differing AP numbers, which form a triangle or a quadrilateral. The performance of the proposed schemes is evaluated via experiments using wireless local area network APs. Results show that the performance of proposed schemes is enhanced compared to that of conventional scheme.

Performance Evaluation of an Indoor Positioning Scheme Using Infrared Motion Sensors

Internet of Things (IoT) for Smart Environments (SE) is a new scenario that collects useful information and provides convenient services to humans via sensing and wireless communications. Infra-Red (IR) motion sensors have recently been widely used for indoor lighting because they allow the system to detect whether a human is inside or outside the sensors’ range. In this paper, the performance of a position estimation scheme based on IR motion sensor is evaluated in an indoor SE. The experimental results show that we can track the dynamic position of a pedestrian in straight moving model as well as two dimensional models. Experimental results also show that higher performance in accuracy and dynamic tracking in real indoor environment can be achieved without other devices.

3D positioning scheme exploiting nano-scale IR-UWB orthogonal pulses

In these days, the development of positioning technology for realizing ubiquitous environments has become one of the most important issues. The Global Positioning System (GPS) is a well-known positioning scheme, but it is not suitable for positioning in in-door/building environments because it is difficult to maintain line-of-sight condition between satellites and a GPS receiver. To such problem, various positioning methods such as RFID, WLAN, ZigBee, and Bluetooth have been developed for indoor positioning scheme. However, the majority of positioning schemes are focused on the two-dimension positioning even though three-dimension (3D) positioning information is more useful especially in indoor applications, such as smart space, U-health service, context aware service, etc. In this paper, a 3D positioning system based on mutually orthogonal nano-scale impulse radio ultra-wideband (IR-UWB) signals and cross array antenna is proposed. The proposed scheme uses nano-scale IR-UWB signals providing fine time resolution and high-resolution multiple signal specification algorithm for the time-of-arrival and the angle-of-arrival estimation. The performance is evaluated over various IEEE 802.15.4a channel models, and simulation results show the effectiveness of proposed scheme.

A Hybrid Positioning Scheme Exploiting Sensors and RSS of Wi-Fi Signals

Abstract As interests and demands for indoor positioning have recently increased, a positioning scheme utilizing the smartphone equipped with various sensors like an acceleration sensor and a geomagnetic sensor has been expected as a high potential and practical candidate for indoor positioning purpose. The acceleration sensor and the geomagnetic sensor are used for the estimation of travelled distance and the direction of movement of pedestrians, respectively. Although it provides very accurate positioning performance, the positioning scheme based only sensors tends to be affected by indoor environments like magnetic field of general indoor office building. In addition, the positioning error is apt to be accumulated as the travelled distance is increased. In this paper, therefore, a new positioning scheme is proposed to compensate the conventional positioning technology and to enhance the positioning performance. The proposed scheme consists with positioning based sensors, multi-lateration and WLAN-ID based on received signal strength (RSS) of Wi-Fi signals. The proposed scheme is evaluated with experiments at general building in university and the performance of the proposed scheme is superior to the conventional schemes such as a positioning scheme with only sensors and a positioning scheme based on RSS of Wi-Fi signals only.

An Enhanced 3D Positioning Scheme Exploiting Adaptive Pulse Selection for Indoor LOS Environments

In this paper, an enhanced 3D positioning scheme exploiting adaptive pulse selection is proposed for indoor environments. The proposed scheme is based on the time-of-arrival and angle-of-arrival estimation with multiple orthogonal pulses and uniform linear arrays antenna in impulse radio ultra-wideband systems. Since the ranging and the angle estimation performances are different from pulse shape and received SNR, the performance of 3D position estimation can be enhanced by adaptively selecting a pulse from received multiple pulses. Based on the orthogonal property, orthogonal pulses can be distinguished at the receiver and thus the optimal pulse is selected from the multiple pulses for ranging, azimuth and elevation angle estimation, respectively. Since the optimal pulse is selected for each estimation, enhanced performance for 3D position estimation can be achieved. The performance of the proposed scheme is evaluated by computer simulations over the IEEE 802.15.4a channel model. Results show that the performance of the proposed scheme is enhanced compared to that of the conventional scheme.

Distributed evacuation guide system based on positioning information of passengers in the subway station

In this paper, a distributed evacuation system based on the positioning information of subway passengers is proposed. Recently, the subway station is becoming complicated by combining with shopping malls, and movie theaters. Compared to the increasing complexity of subway stations, evacuation systems are less complex(ed note: Please check.). Subway passengers in each cell were estimated to use the access point in the subway cells and statistics information. The evacuation route is provided through a direction indicator and push alarm of a smart phone based on estimated the number of passengers and exit information of the subway station. Based on this schemes, a quick and safe evacuation system of subway passengers was proposed. The number of connection passengers was estimated using AP with OpenWrt embedded OS installed. The average error rate of the number of passenger was confirmed to be 15%, 17% and 23% at the confidence parameter of 1 , 2 , and 3 , respectively, through a simulation. The possibility of the system through a simple experiment was examined.

Effects of the Location of APs on Positioning Error in RSS Value Based Scheme

In this paper, the effects of the location of APs on positioning error are discussed in received signal strength (RSS) value based scheme. The RSS values are measured to know the RSS characteristics of AP as the distance between the AP and the receiver is increased. The positioning errors are evaluated with three APs. A triangle is formed with three APs and the errors are distinguished by inside error and outside error, respectively, whether the receiver is located inside the triangle or not. The results indicate the inside errors of triangle, which is formed by three APs, are lower than outside errors.

Performance evaluation of IR-UWB ranging system with various waveforms

In this paper, we evaluate the performance of IR-UWB ranging system, which is based on time of arrival estimation technique, with different UWB waveforms. For high precision ranging performance evaluation, the minimum mean square error and the zero forcing techniques are employed to resolve the multipath components and the ranging performance is evaluated with various waveforms as well as a commonly employed Gaussian waveform. Simulation results show that the root raised cosine waveform outperforms other considered waveforms.