Choong-Ho Cho

Inductively coupled plasma–reactive etching (ICP-RIE) of InGaZnO (IGZO) thin films was studied with variations in gas mixtures of hydrochloride (HCl) and argon (Ar). The dry etching characteristics of the IGZO films were investigated according to radiofrequency bias power, gas mixing ratio, and chamber pressure. The IGZO film showed an excellent etch rate of 83.2 nm/min from an optimized etching condition such as a plasma power of 100 W, process pressure of 3 mTorr, and HCl ratio of 75% (HCl:Ar at 30 sccm:10 sccm). In addition, this ICP-RIE etching condition with a high HCl composition ratio at a moderate RIE power of 100 W showed a low etched pattern skew and low photoresist damage on the IGZO patterns. It also provided excellent surface morphology of the SiO₂ film underneath after the entire dry etching of the IGZO layer. The IGZO thin film as an active layer was successfully patterned under the ICP-RIE dry etching under the HCl-Ar gas mixture, affording an excellent electrical characteristic in the resultant top-gate IGZO thin-film transistor.

KSII Transactions on Internet and Information Systems TIIS Paper Details

In Fractional frequency reuse (FFR) technique, the available physical resource blocks are reused among different cells in a manner that co-channel interference and/or inter-cell interference effect is reduced. However, when the resources are highly utilized, the sharing of these resources becomes exhausted and/or limited, and this leads to a high interference and hence high call blocking probability. Therefore, this paper proposes a call admission control in FFR to improve the performance of the FFR-based cellular system. The results of the two quality of service (QoS) constraints, the call blocking probabilities and the resource utilizations for users are used for some design criteria of the cell inner/outer area to maximize the throughput and hence for the evaluation of the system power efficiency.

The deployment of advanced metering infrastructures on the small-medium scale building facilitates power suppliers and consumers to better control the utility s

Coordinated multi-point transmission (CoMP) with the joint transmission (JT) scheme is employed in cellular networks to improve the data rate, the cell-edge throughput and/or to increase the system throughput. In CoMP-JT, since the user equipment (UE) is capable of receiving the desired signal from an adjacent cell as well as from its serving cell, it can achieve an improved signal to interference ratio. However, this scheme entails exhaustion of resources in serving base station (BS). In this paper, we propose a call admission control scheme (CAC) to improve the performance of CoMP-JT based cellular systems. In this CAC scheme, CoMP-JT technique is applied to UEs located near the edge of a cell. In order to establish an analytical model for CoMP-JT based cellular systems, we introduce a model for traffic analysis using a two-dimensional Markov chain and approximate the computation of the power sum of multiple log-normal random components in a multi-cell environment. Performances of CoMP-JT based cellular systems are evaluated with respect to two quality of service (QoS) constraints pertaining to call-blocking and outage probabilities, respectively from the network-layer and the physical-layer perspectives. We first measure the resource utilization and call blocking probability for the downlink resources for various offered loads in the cell. Based on that, we obtain the outage probability and effective throughput of the system. The analytical results are compared with computer simulations. Finally, we consider the dynamic point selection (DPS) scheme that is a modified version of the JT scheme, in which some resources of adjacent cells are muted.

Power efficiency has become an important design goal for wireless communications, and a coordinated multi‐point (CoMP) with joint transmission (JT) scheme can be implemented to improve the cell edge throughput by increasing the signal‐to‐interference ratio, which in turn leads to power savings through cooperative transmission. To this end, we propose a power control scheme in which the cooperating base station can reduce its own transmission power while remaining within two stage quality of service (QoS) constraints, including the call‐blocking probability and outage probability. For the two QoS constraints, we introduce call admission control and signal‐to‐interference ratio models for CoMP‐JT that consider a two‐dimensional Markov chain and the sum of multiple exponential random components. The results of the call blocking and outage probabilities are used to obtain the power consumption model and analyse the performance for the CoMP‐JT with the proposed power control technique. Both the analytical and numerical results show that the proposed power control strategy can reduce the power consumption for the cellular network with the two stage QoSs. Copyright © 2016 John Wiley & Sons, Ltd.

Virtual simulation technology has been considered as a highly efficient and cost-effective solution for a soldier training system, and evolved into diverse combinations of hardware and software. To maximize the virtual reality effect within a restricted space, a locomotion interface such as an omni-directional treadmill is introduced as a major component of a virtual simulator, therefore real time interaction between human and the virtual simulator becomes very important. Displacement and heading changes of the trainee are crucial information to control the virtual simulator when we implement highly reactive motion control for the omni-directional treadmill and interaction control of the virtual contents. This paper proposes a control parameter estimation algorithm for the virtual training simulator by using two types of motion capture sensors and presents the experimental results. Kinematic joint positions are analyzed to estimate the trainee’s location and velocity for feedback and feedforward control of the omni-directional treadmill. The accuracy of two approaches is evaluated by comparing with the reference system, which gives a ground truth value.

In device-to-device (D2D) communication, users in close proximity to each other can communicate directly without going through a base station; such direct communication can improve spectral efficiency. However, D2D links may generate high interference to cellular user equipment (UE) located in their communication areas if they use the same channel with the UE for data transmission. D2D communication could also generate interference for each D2D pair when the common wireless medium in a co-located limited area is accessed. Although, to solve this problem, research on reducing or avoiding interference between D2D and cellular UE in network supporting D2D communication was conducted, the interference managements are still not fully studied for between D2D pairs. In this paper, we investigate the problem of D2D pair coexistence in which interference is considered between D2D pairs. By analytically deriving an operating condition for D2D pairs deployed within the same region, we provide a lower bound on the throughput of D2D pair networks and the optimal number of D2D pairs that can coexist.