• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.2B
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• pp.215-224
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• 2010

A container security device (CSD) monitors intrusions through the cargo door; it is a reduced function device that uses IEEE 802.15.4 with a beacon mode. However, in the beacon mode, the CSD consumes too much battery power in periodical idle listening and sensing trials. Moreover, the CSD cannot send the message to the CSD reader actively, and it makes big latency problem. Therefore, we propose a low-power CSD to reduce the unnecessary power consumption. The proposed CSD follows the requirements of the U.S. Department of Homeland Security, and reduces battery consumption through a power-efficient hardware design, a night-watch mechanism for low-power operation and low-power sensing to reduce unnecessary monitoring. And the CSD sends alert message to the CSD reader. Simulation results show that our CSD reduces battery consumption by over 70% through the night-watch mechanism and by approximately 80% through the low-power sensing. And the CSD can send the alert message to the remote CSD reader by over 94%.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.4
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• pp.759-764
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• 2009

A new backoff scheme for infrastructure mode in IEEE 802.11 wireless LANs is proposed to improve a performance. Each station generates a unique backoff number using total number of stations, fairness parameter included in beacon frame and an user's ID that is assigned by AP. The station sends a packet after its own backoff number of idle slots, which makes a collision free access among stations within AP's coverage. The proposed method shows better performance in the view of channel utilization and packet delay than an original IEEE 802.11 CSMA/CA backoff scheme.

• The Transactions of the Korean Institute of Power Electronics
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• v.21 no.1
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• pp.19-26
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• 2016

In this study, a bidirectional DC-DC converter for idle stop and go (ISG) is developed to reduce fuel consumption. A three-phase non-isolated half-bridge converter is selected through a design method by considering efficiency and volume. According to the state of charge of the batteries at both the low-voltage and high-voltage sides, buck mode, which charges a low-voltage battery from the generated motor energy, and boost mode, which provides power to the motor from the low- and high-voltage battery sides, are required in the ISG system. Hence, an autonomous and seamless bidirectional control method using a variable current limiter is proposed for mode change. A 1.8 kW engineering sample of the proposed converter has been built and tested to verify the validity of the proposed concept. The maximum efficiencies, including gate driver and control circuit losses, are 96.4% in charging mode and 96.1% in discharging mode.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.2
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• pp.1027-1035
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• 2014

The most important design factor for portable devices is power consumption. In this paper, in the early design stage of a mobile device which measures temperature and humidity a power consumption model will be proposed and then the overall power consumption will be estimated based on this model. We will verify previously the correctness of such estimated power consumption before implementation of the real device. That is our proposed design methodology based on power consumption model. An improved design method for efficiently reducing the current consumption in the idle mode is also presented. By implementing a real prototype of the mobile device for measuring temperature and humidity, the correctness of our proposed design methodology based on power consumption modeling will be verified.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.5
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• pp.2069-2074
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• 2013

The use of the electromagnetic clutch water pump for internal combustion engine vehicles saves fuel and leads to a reduction in emissions. The clutch water pump allows the engine cooling system to select the optimum operation condition by using coolant flow rate on/off control. This study investigated the characteristics of fuel consumption and emissions of the diesel engine cooling system using the clutch water pump. The electromagnetic clutch operation reduced by about 49% of engine warm up period at idle condition and controlled the optimum high coolant temperature at driving condition. Therefore, fuel consumption was enhanced by about 5%, and emissions such as HC, CO and $CO_2$ were also reduced to a certain degree even though NOx increased a little bit, compared to those of the conventional water pump under NEDC mode which represents the real driving pattern.

• Transactions of the Korean Society of Automotive Engineers
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• v.17 no.1
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• pp.19-23
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• 2009

This paper focuses on vehicle fuel economy improvement using D-Range neutral control of automatic transmission. The system objected to reducing of fuel consumption during idle. Usually, turbine of conventional auto transmission is mechanically linked to wheel during idling condition. Therefore speed ratio of torque converter is zero for that period. This causes needless power loss by the torque converter slip. To improve this inefficiency automobile makers develops electronically-controlled D-range neutral control system. The D-range neutral control system minimizes slip on the torque converter by shifting gear to a neutral position during vehicle stoped with D-range gear position. However there's insufficient study about the effect of D-range neutral control system on vehicle fuel economy. In this paper, researches are performed on effect of D-range neutral control system on vehicle fuel economy by experiment with two different vehicle. And it is also estimated the effect on vehicle fuel economy using computer simulation. As a result, 1.8% of LA-4 mode fuel economy improvement can be achieved in a vehicle by D-range neutral control system.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.21 no.6
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• pp.71-76
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• 2021

Recently, as the size of IoT data grows, the memory power consumption of real-time systems increases rapidly. This is because real-time systems always place entire tasks in memory, which increases the demand of DRAM significantly. In this paper, we adopt emerging fast storage media and move a certain portion of real-time tasks from DRAM to storage. The part of tasks in storage are, then, loaded into memory when they are actually used. We incorporate our memory/storage power-saving into the dynamic voltage/frequency scaling of processors, thereby optimizing power consumptions in CPU and memory simultaneously. Specifically, the proposed technique aims at minimizing the CPU idle time and the DRAM memory size by determining appropriate voltage modes of CPU and the swap ratio of memory, without violating the deadlines of all tasks. Through simulation experiments, we show that the proposed technique significantly reduces the power consumption of real-time systems.

• Journal of the Korean Institute of Gas
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• v.15 no.5
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• pp.50-56
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• 2011

A preliminary experimental study of new concept air hybrid engine, which stores compressed air in the tank during braking and re-use it to propel vehicle during crusing or acceleration, was carried out in this study. A single cylinder engine was modified to realize the concept of air hybrid engine. Independent variable valve lift system was adopted in one of the exhaust valves to store the compressed air into the air tank during compression period. An air injector module was installed in the place of spark plug, and the stored compressed air was supplied during the expansion period to realize air motoring mode. For air compression mode, the tank with volume of 30 liter could be charged up to more than 13 bar. By utilizing this stored compressed air, motoring work of 0.41 bar of IMEP(Indicated mean effective pressure) at maximum can be generated at the 800rpm conditions, which is higher than the case of normal idle condition by 1.1 bar of IMEP.