• Journal of Communications and Networks
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• v.7 no.2
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• pp.126-134
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• 2005

Reducing energy consumption in mobile hosts (MHs) is one of the most critical issues in wireles/mobile networks. IP paging protocol at network layer and power saving mechanism (PSM) at link layer are two core technologies to reduce the energy consumption of MHs. First, we investigate the energy efficiency of the current IEEE 802.11 power saving mechanism (PSM) when IP paging protocol is deployed over IEEE 802.11 networks. The result reveal that the current IEEE 802.11 PSM with a fixed wakeup interval (i.e., the static PSM) exhibits a degraded performance when it is integrated with IP paging protocol. Therefore, we propose an adaptive power saving mechanism in IEEE 802.11-based wireless IP networks. Unlike the static PSM, the adaptive PSM adjusts the wake-up interval adaptively depending on the session activity at IP layer. Specifically, the MH estimates the idle periods for incoming sessions based on the exponentially weighted moving average (EWMA) scheme and sets its wake-up interval dynamically by considering the estimated idle period and paging delay bound. For performance evaluation, we have conducted comprehensive simulations and compared the total cost and energy consumption, which are incurred in IP paging protocol in conjunction with various power saving mechanisms: The static PSM, the adaptive PSM, and the optimum PSM. Simulation results show that the adaptive PSM provides a closer performance to the optimum PSM than the static PSM.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.1
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• pp.28-33
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• 2007

In spite of the large interest in the 802.15.4 standard, no realistic experimental research of its behaviour exists to date except a few works by simulations and analytical modeling. In this paper, we have established realistic environment of IEEE 802.15.4 network and analyze its behaviour under various conditions as like 1) maximum throughput of 802.15.4 MAC, 2) MAC fairness. and 3) throughput and m rate under co-existence of 802.11 Wi-Fi wireless networks.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.6
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• pp.116-126
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• 2008

This paper describes the Dual-band WLAN transmitter with 2.4[GHz], 5[GHz]. Dual-band WLAN transmitter was designed at 2.4[GHz] and 5[GHz]. The Dual-band WLAN transmitter has a amplifier which operate at 2.4[GHz] and 5[GHz] frequency and two VCO(Voltage Controlled Oscillator) or VCO has a wide scope of frequency. these problem cause a size and a power consumption, The Dual-band WLAN transmitter module was proposed to solve these. the transmitter was designed to get output signals of IEEE 802.11a's 5.8[GHz] band signal using frequency multiplication way or to act a amplifier about the 2.4[GHz] band signal of IEEE 802.11b/g, according to inputed frequency and bias voltage that a eve using single transmission block. The output spectrum get the improved specification of ACPR of 4[dB], 6[dB], 16[dB] at +11[MHz], +20[MHz], +30[MHz] offset of center frequency compared to no linearization, was satisfied to transmit spectrum mask of IEEE 802.11a wireless Lan.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.9
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• pp.2008-2015
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• 2010

Ns-2 is a proven simulator which is widely utilized to evaluate the performance of wired and wireless network. Ns-2.33 version introduced the extended version including the modules which the core functions of existing 802.11 PHY and MAC layer are implemented. However, if the error rate, one of most important parameters to evaluate a performance of wireless network, is applied to the extended version, the simulation is ceased with several fatal errors. Furthermore, a packet error is detected and discarded on MAC layer in the traditional protocol architecture, but there is the problem which can't identify information about a packet with error by processing packet error on PHY layer in this version. In this paper, we modify the extended version to resolve the above mentioned problems. And also we perform ns-2 simulation using the modified version on the IEEE 802.11p based vehicular ad-hoc networks, and then analyze effects of error rate.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.8
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• pp.9-18
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• 2004

The IEEE 802.11 Distributed Coordination Function(DCF) protocol provides a contention-based distribution channel access mechanism for stations to share the wireless medium. However, the performance of the DCF drops dramatically in terms of throughput, delay and delay jitter as the number of active stations becomes large. In this paper, we propose a simple and effective scheme, called DCF/VG(Distributed Coordination Function with Virtual Group), for improving the performance of the IEEE 802.11 DCF mechanism. In this scheme, each station independently decides the virtual group cycle using the information provided by the carrier sensing mechanism. The virtual group cycle consists of one or more virtual groups and a virtual group includes an idle period and a busy period. Each station operates in only one out of several virtual groups of the virtual group cycle and does not operate in the others. In other words, each station decreases its backoff counter and tries to transmit a packet only in its virtual group like the IEEE 802.11 DCF. Performance of the proposed scheme is investigated by numerical analysis and simulation. Numerical and simulation results show that the proposed scheme is very effective and has high throughput and low delay and jitter under a wide range of contention level.

• Journal of Korea Society of Industrial Information Systems
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• v.20 no.2
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• pp.39-44
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• 2015

Restricted Access Window (RAW) has been designed to improve power saving efficiency by reducing collisions of contending stations in the IEEE 802.11ah Wireless Local Area Networks (WLANs). We conduct simulations in order to observe the stations' operations influencing the lengths of the Restricted Access Window (RAW). From the observation, we consider how to adjust the stations' operations for proper RAW managements.

• Journal of information and communication convergence engineering
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• v.6 no.3
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• pp.343-347
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• 2008

Wakeup schemes that turn off sensors' radio when communication is not necessary have great potential in energy saving. At the start of each beacon interval in the IEEE 802.11 power saving mode specified for DCF, each node periodically wakes up for duration called the ATIM Window. However, in the power saving mechanism specified in IEEE 802.11, all nodes use the same ATIM window size. Since the ATIM window size critically affects throughput and energy consumption, a fixed ATIM window does not perform well in all situations. This paper proposes an adaptive mechanism to dynamically choose an ATIM window size according to network condition. Simulation results show that the proposed scheme outperforms the IEEE 802.11 power saving mechanism in terms of the amount of power consumed and the packet delivery ratio.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.3
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• pp.556-562
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• 2007

In this paper we propose a new method which adjusts the collision resolution depending on busy status of the channel to improve performance of IEEE 802.11 DCF. This scheme reduces the number of collisions in wireless channel by decreasing the amount of movements of each station's backoff stage based on busy event count and the one stage backoff model. Through simulation, we compared the performance of our scheme with that of DCF, ADCF and SD.

• Proceedings of the IEEK Conference
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• 2002.06a
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• pp.121-124
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• 2002

The IEEE 802.lla PLCP H/W for Processing efficiently control message between MAC and PHY is designed. Slate machine and clock control according to rate is designed and timing diagram is verified on the FPGA simulation environment.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.11
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• pp.2062-2068
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• 2008

In a u-City project in Busan, public transportation which is one of ITS has been considered. RFID system embedded with PXA255 chip and middleware capable of communicating a server side was developed. To perform data communication link with traffic card, developed system consists of wireless modules that are wireless LAN (IEEE802.11a/b and IEEE802.16. Using developed RFID system and middleware, it is expected that this system becomes a basic infrastructure to support a service of u-Traffic for u-City construction.