• Journal of ILASS-Korea
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• v.22 no.1
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• pp.13-21
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• 2017

The fog screen is a device projecting the media to the aerosol flow field. As major parameters to generate dense and steady fog screen, shear stress, optical blockage ratio and SMD were obtained result through experiment. The micro droplet was generated by the piezo oscillation element, and the aerosol flow mixed with an air flow was sprayed into the vertical direction from the top of the fog screen through the 280 mm slot. For produce a dense, uniform fog screen, the shear effect, optical blockage ratio and SMD between aerosol and air curtain were measured. The minimum and maximum shear stress conditions were selected and it was confirmed that the optical transmission deviation of the aerosol flow field was small when the aerosol and air curtain flow rates were changed. When the aerosol and air curtain flow power were 18 V (1.51 m/s) and 24 V (2.55 m/s), respectively, under the condition of the minimum shear stress and laminar flow, the optical blockage ratios with the spray length were small, and it produced a most stable and high density uniform fog screen by injecting a constant of $10{\mu}m$ or less.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.6
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• pp.3-9
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• 2015

We investigate rate scheduling and power allocation problem for a delay constrained CDMA systems. Specifically, we determine an energy efficient scheduling policy, while each user maintains the short term (n time slots) average throughput. We consider a multirate CDMA system where multirate is achieved by multiple codes. Each code can be interpreted as a virtual user. The aim is to schedule the virtual users into each time slot, such that the sum of transmit energy in n time slots is minimized. We then show that the total energy minimization problem can be solved by a shortest path algorithm. We compare the performance of the optimum scheduling with that of TDMA-type scheduling.

• JSTS:Journal of Semiconductor Technology and Science
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• v.7 no.3
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• pp.166-176
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• 2007

Radio frequency (RF) microelectromechanical systems (MEMS) have been pursued for more than a decade as a solution of high-performance on-chip fixed, tunable and reconfigurable circuits. This paper reviews our research work on RF MEMS switches and switching circuits in the past five years. The research work first concentrates on the development of lateral DC-contact switches and capacitive shunt switches. Low insertion loss, high isolation and wide frequency band have been achieved for the two types of switches; then the switches have been integrated with transmission lines to achieve different switching circuits, such as single-pole-multi-throw (SPMT) switching circuits, tunable band-pass filter, tunable band-stop filter and reconfigurable filter circuits. Substrate transfer process and surface planarization process are used to fabricate the above mentioned devices and circuits. The advantages of these two fabrication processes provide great flexibility in developing different types of RF MEMS switches and circuits. The ultimate target is to produce more powerful and sophisticated wireless appliances operating in handsets, base stations, and satellites with low power consumption and cost.

• IEIE Transactions on Smart Processing and Computing
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• v.4 no.2
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• pp.65-70
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• 2015

In this paper, we describe the world's first real-time ray-tracing chip architecture. Ray-tracing technology generates high-quality 3D graphics images better than current rasterization technology by providing four essential light effects: shadow, reflection, refraction and transmission. The real-time ray-tracing chip named RayChip includes a real-time ray-tracing graphics processing unit and an accelerating tree-building unit. An ARM Ltd. central processing unit (CPU) and other peripherals are also included to support all processes of 3D graphics applications. Using the accelerating tree-building unit named RayTree to minimize the CPU load, the chip uses a low-end CPU and decreases both silicon area and power consumption. The evaluation results with RayChip show appropriate performance to support real-time ray tracing in high-definition (HD) resolution, while the rendered images are scaled to full HD resolution. The chip also integrates the Linux operating system and the familiar OpenGL for Embedded Systems application programming interface for easy application development.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10b
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• pp.686-693
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• 1998

Prestressed Concrete Cylinder Pipe(PCCP) is used in water transmission pipeline of the Great Man-made River Project(GMR Project). In domestic area, PCCP is used for water cooling systems of Uljin and Youngkwang nuclear power plants. In abroad, especially in the United States and Canada PCCP supplies virtually every metropolitan area with raw and treated water. Compared with other pipe types, PCCP manufacturing cost is dear. But total cost can be considered as economical due to low installation and maintenance cost. Previously, the designs of PCCP were generally determined from one of two appendices in American Water Works Association(AWWA)standard C301 which provided two design methods-cubic parabola design method and stress analysis design method. In 1992, the design procedure for PCCP expanded from two alternatives to the most huge and complex AWWA standard C304. Because C304is so large, it takes too much time for the engineer to read and understand the design concepts and procedures. In this paper, the AWWA C304 design procedures are segmented into simple, understandable sections and concepts and explained. Each section or concepts is compared to the previous design procedure to highlight the revisions and reasons for them. Also the PCCP design program was developed and the design program results are compared with the calculations of the GMR project design consultant.

• The Transactions of the Korea Information Processing Society
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• v.2 no.3
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• pp.374-381
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• 1995

For designing radio communication systems, radio-channel effects must be considered in order to obtain the desired communication quality, transmitting power, transmission speed and bit error rate. In radio channel, one of major factors that degrade communication quality is multipath fading between transmitting and receiving points. Therefore, a channel model which can describe fading effects correctly is requested. This paper deals with the composition of the channel simulator model that describes multipath fading effects and delay times which occur in the channel. For the performance analysis of the proposed model, trandmitting signal is used in the simulation. From simulation results, it can be shown that probability density function. level crossing rates and average fading-duration time distribution of the faded receive signal are very similar with theoretic values.

• Journal of Communications and Networks
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• v.15 no.4
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• pp.422-429
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• 2013

Advances in wireless sensor network (WSN) technology have enabled small and low-cost sensors with the capability of sensing various types of physical and environmental conditions, data processing, and wireless communication. In the WSN, the sensor nodes have a limited transmission range and their processing and storage capabilities as well as their energy resources are limited. A triple umpiring system has already been proved for its better performance in WSNs. The clustering technique is effective in prolonging the lifetime of the WSN. In this study, we have modified the ad-hoc on demand distance vector routing by incorporating signal-to-noise ratio (SNR) based dynamic clustering. The proposed scheme, which is an efficient and secure routing protocol for wireless sensor networks through SNR-based dynamic clustering (ESRPSDC) mechanisms, can partition the nodes into clusters and select the cluster head (CH) among the nodes based on the energy, and non CH nodes join with a specific CH based on the SNR values. Error recovery has been implemented during the inter-cluster routing in order to avoid end-to-end error recovery. Security has been achieved by isolating the malicious nodes using sink-based routing pattern analysis. Extensive investigation studies using a global mobile simulator have shown that this hybrid ESRP significantly improves the energy efficiency and packet reception rate as compared with the SNR unaware routing algorithms such as the low energy aware adaptive clustering hierarchy and power efficient gathering in sensor information systems.

• ETRI Journal
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• v.37 no.3
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• pp.480-490
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• 2015

The reliability of sensor networks is generally dependent on the battery power of the sensor nodes that it employs; hence it is crucial for the sensor nodes to efficiently use their battery resources. This research paper presents a method to increase the reliability of sensor nodes by constructing a connected dominating tree (CDT), which is a subnetwork of wireless sensor networks. It detects the minimum number of dominatees, dominators, forwarder sensor nodes, and aggregates, as well as transmitting data to the sink. A new medium access control (MAC) protocol, called Homogenous Quorum-Based Medium Access Control (HQMAC), is also introduced, which is an adaptive, homogenous, asynchronous quorum-based MAC protocol. In this protocol, certain sensor nodes belonging to a network will be allowed to tune their wake-up and sleep intervals, based on their own traffic load. A new quorum system, named BiQuorum, is used by HQMAC to provide a low duty cycle, low network sensibility, and a high number of rendezvous points when compared with other quorum systems such as grid and dygrid. Both the theoretical results and the simulation results proved that the proposed HQMAC (when applied to a CDT) facilitates low transmission latency, high delivery ratio, and low energy consumption, thus extending the lifetime of the network it serves.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.5
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• pp.8-15
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• 2011

LTE-Advanced aims at peak data rates of 1Gbits/s for the downlink and 500 Mbits/s for the uplink, which can be accomplished only by using wide spectrum allocation of 100MHz as well as advanced multiple input multiple output antenna techniques to the uplink. This paper analyzes the uplink precoding techniques which include LTE codebook of downlink, singular value decomposition codebook, and equal gain transmission codebook over LTE defined single carrier frequency division multiplexing systems. Finally considering nonlinear transmit power amplifier model, it is shown that link-level performance of EGT is superior to those of any other precoding schemes.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.1C
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• pp.113-119
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• 2009

The training sequence with the appropriate length for equalization and initial synchronization is necessary before sending the pure data in the burst transmission type DS-UWB system. The length of the training sequence is one of the factors which make throughput decreased. The noble structure with the variable length of the training sequence whose length can be adaptively tailored according to the channel conditions (CM1,CM2,CM3,CM4) in the DS-USB systems is proposed. This structure can increase the throughput without sacrificing the performance than the method with fixed length of training sequence considering the worst case channel conditions. Simulation results under IEEE 802.15.3a channel model show that the proposed scheme can achieve higher throughput than a conventional one with the slight loss of BER performance. And this structure can reduce the computation complexity and power consumption with selecting the short length of the training sequence.