• Journal of KIISE:Computing Practices and Letters
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• v.15 no.10
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• pp.724-739
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• 2009

This paper suggests the energy-efficient message delivery scheme and the software platform which exploits the multiple network interfaces of the mobile terminals and GPS in the current mobile devices. The mobile terminals determine the delivery method among 'direct', 'indirect', and 'WAN' based on the position information of itself and other terminals. 'Direct' method sends a message directly to the target terminal using local RAT. 'Indirect' method extends the service area by exploiting intermediate terminals as relay node. If the target terminal is too far to reach through 'direct' or 'indirect' method, the message is sent using wireless WAN technology. Our proposed scheme exploits the position information and, thus, power consumption is drastically reduced in determining handover time and direction. Network simulation results show that our proposed delivery scheme improves the message transfer efficiency and the handover detection latency. We implemented a message platform in a smart phone realizing the proposed delivery scheme. We compared our platform with other typical message platforms from energy efficiency aspect by observing the real power consumption and applying the mathematical modeling. The comparison results show that our platform requires significantly less power.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.1
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• pp.84-92
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• 2000

A GaAs MESFET MMIC transmitter for 2.4 GHz wireless local loop handset is designed and fabricated. The transmitter consists of a double balanced active mixer and a two stage driver amplifier with voltage negative feedback. In particular, a pair of CS-CG(common source-common gate) structure compensates the reduction in dynamic range caused by unbalanced complementary IF input signals. And to suppress the leakage local power at RF port, the mixer is designed by using phase characteristic between the ports of MESFET. At the bias condition of 2.7 V and 55.2 mA, the fabricated MMIC transmitter with chip dimensions of $0.75\times1.75 mm^2$ obtains a measured conversion gain of 38.6 dB, output $P_{idB}$ of 11.6 dBm, and IMD3 at -5 dBm RF output power of -31.3 dBc. This transmitter is well suited for WLL handset.

• Journal of Korean Academy of Fundamentals of Nursing
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• v.19 no.4
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• pp.434-443
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• 2012

Purpose: This study was conducted to investigate sleep patterns in nursing students as measured by an automated wireless sleep tracker and self-reported sleep scales. Methods: Data were collected from October, 2011 to May, 2012. ZQ (a symbolic number that measures the quality and quantity of sleep) was calculated from the automated wireless sleep tracker. Pittsburgh Sleep Quality Index-Korean version, Sleep scale A, and sleep satisfaction were used as self-report sleep scales. Female nursing college students (n=37) were recruited by convenience sampling. Before going to bed, they were asked to put on a head-band type sleeping sensor and to move it the next morning. Every student slept 2~4 nights with the sleep tracker. Data were collected for 86 (91.4%) of 94 nights' sleep. The students were also requested to fill in the PSQI-K, sleep scale A, and sleep satisfaction. Results: The only statistically significant correlation was between ZQ and sleep satisfaction (r=.869, p=.026). The biggest obstacle in using this device was putting on the head-band type sensor. Conclusion: Validity of the wireless sleep tracker was verified in part. The usefulness of this device in nursing research and practice was identified. Further evaluation need to be conducted with various populations.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.65 no.1
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• pp.72-75
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• 2016

In this paper, we proposes a internal antenna for wireless DVI dongle device using the folded monopole structure. The proposed antenna uses a basic structure of spiral and monopole. The antenna optimized for parameters length, gap, width, and rectangle of folded monopole antenna using the spiral structure. To confirm the characteristics of the antenna parameters, HFSS from ANSYS Inc. was used for the analysis. We used an FR4 dielectric substrate with a dielectric constant of 4.4. The DVI dongle size of the proposed antenna is $50{\times}40{\times}1.6mm$, and the size of the antenna area is $10{\times}40mm$. There is a value of return loss less then -10dB in 2.4GHz and 5.8GHz, band and the maximum antenna gain is -4.13dBi. The utilization possibility of the wireless DVI Dongle antenna have a folded monopole with spiral shape could be confirmed according to compare and analyze the simulation and measurement data.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.64 no.2
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• pp.50-56
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• 2015

This paper presents a smart monitoring technique for photovoltaic power systems by using wire and wireless communication networks in which the RS-232/484 and the Zigbee communication networks are inherently established respectively. In the proposed monitoring systems, environmental data sequences and the output power measured by sensors in photovoltaic systems are transferred to PC systems via two communication networks. We made electronic hardware boards for sensors and communication networks to construct its real-time monitoring system and carry out experiments for demonstrating reliability of the proposed monitoring system.

• Journal of Digital Convergence
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• v.12 no.3
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• pp.227-235
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• 2014

Mobile virtualization is an approach to mobile device management in which two virtual platforms are installed on a single wireless device. A smartphone, a single wireless device, might have one virtual environment for business use and one for personal use. Mobile virtualization might also allow one device to run two different operating systems, allowing the same phone to run both RTOS and Android apps. In this paper, we propose the techniques to virtualize the cores of a multicore, allowing the reassign any number of vCPUs that are exposed to a OS to any subset of the pCPUs. And then we also propose the real-time scheduling method to assigning the vCPUs to the pCPU. Suggested technology in this paper solves problem that increases time of real-time process when interrupt are handled, and is able more to fast processing than previous algorithm.

• Journal of the Korea Institute of Military Science and Technology
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• v.2 no.2
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• pp.117-130
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• 1999

In this paper, the performance of data communication function of military radio equipment P-999K is analyzed based on the standard CSMA/CA protocol which is DFWMAC standard protocol done by IEEE802.11 work group. Basic three standard protocols, i.e. Basic CSMA/CA, Stop & Wait ARQ and 4-Way Handshake CSMA/CA protocols are analyzed and compared with each other under the hidden terminal environment. The computer simulation is also done by using SIMSCRIPT II.5 which is popular software tool for an independent processing. The results show that p-persistent(with p=0.3) CSMA scheme is superior to non-persistent CSMA scheme with non-hidden terminal condition, but the performances of both schemes are almost same with hidden terminal situation. And the results of computer simulations are also showed that Basic CSMA/CA protocol is superior to the other protocols when the ratio of hidden terminals is below 10 % of total user population, however, with the above 20% hidden terminals environment and the higher offered traffic conditions the 4-Way Handshake CSMA/CA protocol shows the most superior performance.

• Journal of Digital Contents Society
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• v.6 no.2
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• pp.101-106
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• 2005

In this paper, performance evaluation of mobile access layer for multiple-input multiple-output (MIMO) MultiCarrier(MC)/CDMA 16 QAM system is considered to mitigate multiple access interference and enhance system channel capacity in Rayleigh wireless fading channel. Traditionally, multi-path is viewed as an undesirable feature of wireless communications. Therefore, diversity and adaptive array schemes are proposed to mitigate its effects. Recently, to increase the spectrum efficiency and the link reliability, MIMO schemes is devised to exploit multi-path in a scattering wireless channel. In particular, the channel capacity of MIMO-MC/CDMA 16 QAM system is evaluated according to Eb/No, Mc, p. From the results, in order to improve the channel capacity, the signals at various elements must be uncorrelated. And if the paths are correlated due to inappropriate spacing or mutual coupling effects, the channel capacity of MIMO-MC/CDMA 16 QAM system becomes substantially smaller.

• Journal of Digital Convergence
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• v.12 no.3
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• pp.249-254
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• 2014

Wireless LAN system is evolving toward high-speed data transmission and more accurate channel estimation is necessarily required to improve communication performance. The PLCP preamble field in IEEE 802.11 based wireless MODEM consists of ten short symbols and two long symbols and is used for synchronization and channel estimation. The existing least square (LS) channel estimation is based on only two long training symbols. After estimating channel response separately by using each long training symbol, the final channel estimation is obtained by the average of each estimation. In this paper, a new channel estimation algorithm is presented to improve the performance of the existing LS channel estimation algorithm. From the fact that the short training symbol consists of 12 non-zero subcarriers, it gives us a clue of being able to additionally estimate at least one fourth of channel coefficients. The new LS algorithm performs channel estimation based on both two long training symbols and a short training symbol. The proposed LS algorithm shows a little bit performance improvement over the existing LS estimation and it will be able to be applied to the IEEE 802.11p WAVE system.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.11
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• pp.61-66
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• 2005

This paper describes a 10-bit 210MHz CMOS current-mode Digital-to-Analog Converter (DAC) consisting of 6 bit MSB current cell matrix Sub-DAC, 2 bit mSB unary current source Sub-DAC, and 2 bit LSB binary weighting Sub-DAC for Wireless LAN application. A new deglitch circuit is proposed to control a crossing point of signals and minimize a glitch energy. The proposed 10-bit CMOS current mode DAC was designed by a $0.35{\mu}m$ CMOS double-poly four-metal technology rate of 210MHz, DNL/INL of ${\pm}0.7LSB/{\pm}1.1LSB$, a glitch energy of $76pV{\cdot}sec$, a SNR of 50dB, a SFDR of 53dB at 200MHz sampling clock and power dissipation of 83mW at 3.3V