• Journal of Korea Multimedia Society
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• v.2 no.3
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• pp.329-338
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• 1999

In this paper we propose a WATM MAC protocol called DTDD/PS (Dynamic Time Division Duplex using Poll/Select scheme). The idea of the DTDD/PS protocol is based that a radio cell is considered as queueing system. The MAC controller in base station is charged in coordinating terminals for the QoS requirement from each terminal. For that reason, terminals send it's own dynamic parameter represented its status, and controller controls the access of terminals and assigns time slots dynamically using received parameters. Therefore this system can satisfy the QoS of real-time service in wireless environments. To evaluate DTDD/PS protocol simulations are executed. In 25Mbps channel capacity, the voice and data coexist traffic situation, as the total number of terminal is increased, the delay of data terminals is increased rapidly. But the case of only increasing data terminals, the number of supported voice terminals is not varying. Therefore we can expect that DTDD/PS protocol can applied to multimedia traffic effectively.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.6B
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• pp.1004-1014
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• 1999

MAC protocols in wireless ATM has to increase and maintain the system throughput performance. To achieve these purposes, this paper proposes a dynamic control algorithm called DSPA (Dynamic Signalling Period Allocation) for wireless ATM MAC protocol. The proposed DSPA algorithm consists of the following three algorithms. First, a control slot generation algorithm which generates the control slots by utilizing static and dynamic parameters from the terminals, is proposed. Second, a dynamic signalling period allocation algorithm is proposed for a base station to dynamically determine each signalling period according to current terminal states, and thus allocates the optimal signalling periods. Finally, a dynamic slot allocation algorithm is proposed to dynamically determine priorities of the terminals whenever a slot is allocated. Simulation results indicates that DSPA algorithm decreases average packet delay of the terminals by dynamic allocation of signal periods based on the system utilization, and thus increases the limitation of allowable loads that quarantee quality of services. Also the proposed algorithm is shown to maintain stable throughput even in the case of traffic variations.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.1
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• pp.46-52
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• 2010

A compact circular microstrip patch antenna with a switchable circular polarization(CP) is proposed at 2.4 GHz. An unequal cross-shaped slot on a ground plane is utilized as a perturbation. By switching pin diodes mounted on the slot, the CP sense of each antenna can be simply switched from left-handed(LH) CP to right-handed(RH) CP vice versa. Since the perturbation can be made on the ground plane and no bias circuit is required on the patch side, the bias circuit has not effect on the main beam radiation. From the experimental results, the impedance bandwidth and CP bandwidth of the proposed antenna have shown up to 150 MHz and 35 MHz, respectively. The peak gain of the proposed antenna is 1.7 dBi for both CP senses.

• The Journal of the Korea institute of electronic communication sciences
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• v.5 no.4
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• pp.450-456
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• 2010

In the high-speed packet service, next generation mobile communication system has emerged as a major feature. If the fire of these high-speed kit services and non-continuous transmission of data due to the symmetrical nature of daeyiteo traffic for D-CDMA system has been actively studied. Small amounts of data moving in the uplink, but the real-time video downlink transmission, such as downloading large files to move data and services to those with asymmetric traffic characteristics, a system that can efficiently handle the data requirements be. Of 3GPP TDD(Time Division Duplex) scheme based on CDMA and TDMA in a way by introducing the concept through the proper allocation of time slots that can handle asymmetric traffic efficiently, has an advantage. TD-CDMA system by considering the characteristics of the frame configuration of transmission methods, such as physical channel structure and channel coding has been investigated. In addition, the HARQ scheme TD-CDMA system performance is analyzed by comparing them.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.7
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• pp.1537-1543
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• 2010

This paper describes a compact microstrip antenna with dual polarization characteristics. The antenna, receiving both a left-hand circularly polarized(LHCP) wave and a right-hand circularly polarized(RHCP) wave, can be used for a polarization diversity. A diamond-shaped patch with internal empty room is designed for impedance matching as well as size reduction. And slots are added around feeding point to improve input matching. The proposed antenna has been applied to GPS(global positioning system), operating at 1.57GHz. And, the proposed idea has been verified and estimated by simulation. The measurement results show that it has VSWR 2:1 bandwidth of 83MHz, 3dB axial bandwidth of about 58MHz, 3dB beamwidth of 90degree, and gain of 0dBi, respectively, for RHCP. Also, it has similar performances for LHCP.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.8
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• pp.679-686
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• 2013

Power efficiency becomes more important in wireless LANs as the mobile stations send more data with limited batteries. It has been known that the IEEE 802.11 PSM is not efficient in high load networks: AP cannot deliver buffered packets to a PS station immediately and it can lead the station to stay in active state quite long and result in energy waste. Moreover, it is inefficient that only one data frame is retrieved by a PS-POLL frame. In this paper, we propose a time slotted scheme to enhance the PSM, in which a mobile station can reserve time slots to receive data frames. Our mechanism can reduce collisions by reservation and decrease the channel occupancy by transmitting multiple data frames via one PS-POLL. The analytic model and simulation results show that proposed scheme reduces power consumption significantly and enhances the performance of PSM.

• The Journal of the Korea Contents Association
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• v.14 no.11
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• pp.628-643
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• 2014

The idea to conduct this study stemmed from the following question: What is the appropriate interpretation of the recent change in the user behavior of radio listeners? For some terrestrial radio programs, traditional listeners who mainly listen to them real-time through terrestrial radio broadcasting has been outnumbered by those who access them on smartphones and other mobile devices in a nonlinear way outside the pre-scheduled time slots of the programs. In the research, how terrestrial radio listeners use the new service called podcasting to access and consume audio content were examined by using Q methodology. As a result, three different types of user behavior and perception were modeled. This shows a prominent change in radio content use, which is moving away from the conventional user behavior pattern of radio content, one of the key media for mass communication in the 20th century. Such a development opens up new opportunities to create the same or even a greater user base compared to the existing one for terrestrial radio programs with the users' newly gained mobile access and to replace current radio content by using podcasting as a new service.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.7 no.3
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• pp.142-146
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• 2014

In this paper, an antenna which has quad band in GSM/DCS/PCS/Bluetooth is proposed. This structure is designed with miniaturization for wide band characteristic based on monopole antenna and log-periodic toothed trapezoid patch antenna which has slots. To achieve multi-bandwidth is used the microstrip line on the substrate. An antenna size is $35mm{\times}20mm$ on FR-4(${\varepsilon}r=4.4$) ground substrate of $35mm{\times}75mm{\times}1mm$ size. And proposed antenna is satisfied with impedance bandwidth(VSWR ${\leq}$ 3). The simulated maximum radiation gain is 1.92 dBi, 3.26 dBi, 3.97 dBi at the center frequency of 0.92 GHz, 1.97 GHz, 2.45 GHz, respectively.

• Journal of Advanced Navigation Technology
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• v.6 no.2
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• pp.158-167
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• 2002

In this paper, it is analyzed that WAP packet transmission time to improve performance of WAP using SAR-QT algorithm in Bluetooth channel. The order for SAR-QT algorithm to improve the transfer capability, it is fragmented in WTP total messages that are coming down from upper layer and then the packets are sent one at time in baseband. And it is studied that transmission time for WAP over Bluetooth according to DMI, DM3 or DM5 packet type using SAR-QT algorithm in Bluetooth piconet environment. This SAR-QT algorithm decreases WAP packet transmission time of L2CAP baseband packets by sending packet that are spanning multiple slots. From the results, in WAP over Bluetooth channels, it is found out that WTP packet size ought to be increased to decrease transmission time of WAP packet. In addition, considering BER in wireless channel, optimal WTP packet size is achieved for WAP over Bluetooth in a Rician fading environment.

• KIISE Transactions on Computing Practices
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• v.22 no.6
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• pp.268-277
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• 2016

IoT (Internet of Things) technologies have largely contributed to our smart living environment. The smart parking system is one of the prominent services that IoT supports. To identify the parked vehicles, the previous parking system use special identifying devices, the RFID tags carried by the users, and the high quality camera to recognize the vehicle license numbers. However, the previous methods cause cost inefficiency and unfriendly usages. To address these problems, we propose a smart parking system based on ultrasonic sensors and Bluetooth communication. The proposed system decides the available slots by using the sensor motes located in the parking spaces. Also it recognizes the location of the parked vehicle using Bluetooth RSSI between a Smartphone and the sensor motes. In addition, based on these converging technologies, it can support the parked routes of vehicles for users. To evaluate the implemented smart parking system, we applied the RSSI transform equations and the recognition rate for parked vehicles. As a result, the accurate rate of transformed distances could be measured.