• Journal of Korea Multimedia Society
• /
• v.10 no.6
• /
• pp.745-753
• /
• 2007

The wireless medium is known to be time-varying which could affect and result to a poor network's performance. As a solution, an opportunistic scheduling and power control algorithm based on IEEE 802.11 MAC protocol is proposed in this paper. The algorithm opportunistically exploits the channel condition for better network performance. Convex optimization problems were also formulated i.e. the overall transmission power of the system is minimized and the "net-utility" of he system is maximized. We have proven that an optimal transmission power vector may exist, satisfying the maximum power and SINR constraints at all receivers, thereby minimizing overall transmission power and maximizing net-utility of the system.

• Proceedings of the Korean Information Science Society Conference
• /
• 2010.06d
• /
• pp.262-265
• /
• 2010

멀티미디어 스트리밍은 인터넷에서 이미 가장 인기있는 서비스가 되었다. 멀티미디어 스트리밍 서비스를 제공하기 위해서는 충분한 대역폭과 딜레이가 유지되어야 한다. 기존의 무선 멀티홉 네트워크는 이러한 요구사항을 만족하기 어렵다. 본 논문에서는 멀티미디어 스트리밍을 보다 좋은 품질로 서비스하기 위해 802.11e를 사용한 Hop Based Priority 테크닉을 제안한다. HBP 테크닉은 패킷이 경로를 따라 이동할때 한홉이 지날때마다 우선순위를 증가시킨다. 그럼으로써 먼저 보낸 패킷과 나중에 보낸 패킷간의 경쟁을 최소화 시키고 먼저 보낸 패킷이 채널을 잡을수 있도록 한다. 이를 모델링을 통해 검증하여 약 43%의 성능 개선 효과가 있음을 확인하였다.

• Journal of Communications and Networks
• /
• v.15 no.2
• /
• pp.132-141
• /
• 2013

In this paper, we present diversity coded orthogonal frequency division multiplexing (DC-OFDM), an approach to maximize the probability of successful reception and increase the reliability of OFDM-based systems through diversity coding. We focus on the application of DC-OFDM to vehicular networks based on IEEE 802.11p technology and analyze the performance improvement using this new technology. It is shown that DC-OFDM significantly improves the performance of vehicular ad hoc networks in terms of throughput and the expected number of correctly received symbols.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2005.11a
• /
• pp.883-886
• /
• 2005

This paper proposed a wireless measurement system (WMS) for an effective condition monitoring using wireless communication. WMS consists of two parts: transmitter(TM) acquired a dynamic signal from physical system using ICP type accelerometer sensor. An acquired signal modulated through the low/high pass filter and amplifier in DAQ board, which converted to digital signal. Embedded board(E-board) transferred digital signals to base station(BS) through the socket IEEE.802.11.b. BS is adopted IOCP server structure. Because it can acquired signal well during transferred digital signal. Signal processing used LabVIEW Library, BS(server) designed to realize multi-thread using visual C++.NET for 1 many meaning data processing

• Journal of the East Asian Society of Dietary Life
• /
• v.19 no.5
• /
• pp.798-802
• /
• 2009

This study was performed to assess the presence of contaminated microorganisms of Escherichia coli, Clostridium perfringens, and Bacillus cereus in the 112 commercial Saengshik products. E. coli was not detected in all the samples, but C. perfringens was detected in 11 products (9.8%). The number of the bacteria was less than 100 CFU/g, which was satisfactory to KFDA microbiological requirement. B. cereus was detected less than $10^2{\sim}10^3$ CFU/g in 7 products and $10^3{\sim}10^4$CFU/g in 13 products out of 25 products. Those detected bacteria from tryptose sulphite cycloserine agar and mannitol egg yolk polymyxin agar showed the typical characteristics of Gram positive and contained lecithinase, which can decompose egg-yolks layers in the biochemical test. Therefore, much more attention must be applied to satisfy the B. cereus requirement for Saengshik products sold in the market.

• Journal of KIISE:Information Networking
• /
• v.35 no.5
• /
• pp.409-414
• /
• 2008

In mobile ad hoc networks, most of on demand routing protocols such as DSR and AODV do not deal with traffic load during the route discovery procedure. To solve the congestion and achieve load balancing, many protocols have been proposed. However, the existing load balancing schemes has only considered avoiding the congested route in the route discovery procedure or finding an alternative route path during a communication session. To mitigate this problem, we have proposed a new scheme which considers the packet bursting mechanism in congested nodes. The proposed packet bursting scheme, which is originally introduced in IEEE 802.11e QoS specification, is to transmit multiple packets right after channel acquisition. Thus, congested nodes can forward buffered packets promptly and minimize bottleneck situation. Each node begins to transmit packets in normal mode whenever its congested status is dissolved. We also propose two threshold values to define exact overloaded status adaptively; one is interface queue length and the other is buffer occupancy time. Through an experimental simulation study, we have compared and contrasted our protocol with normal on demand routing protocols and showed that the proposed scheme is more efficient and effective especially when network traffic is heavily loaded.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.34 no.11B
• /
• pp.1272-1282
• /
• 2009

This paper consists of two parts: the protocol for tag-to-tag mesh network and the implementation of dual-radio RFID system. Recently, RFID has been adopted in ports or warehouse, being attached to containers and palettes for loading/unloading automation. However, the RFID system has encountered one problem - some tags cannot receive any command from reader intermittently due to signal interference by containers or field equipments (e. g. cranes and yard tractors). This area where reader signal cannot reach is called dead-zone. The proposed method for solving the dead-zone problem is as follows. A zone which can be communicated directly between readers and tags communicates in 433MHz frequency band in compliance with ISO/IEC 18000-7 standard. On the other hand, dead-zone communicates in 2.4GHz frequency band by using tag-to-tag mesh network in compliance with IEEE 802.15.4 standard. The proposed method can not only save much cost to install additional readers but also help resolve the dead-zone problem. Furthermore, it can provide the easier, faster, and more economical network infrastructure.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.43 no.8 s.350
• /
• pp.91-96
• /
• 2006

High efficiency switching mode circuits such as class I amplifiers have been well known in the MHz frequency range. The class E amplifier is a type of switching mode amplifier offering very high efficiency approaching 100%. In this paper, the class E amplifier has been designed by using the harmonic balance method of circuit simulator. The designed amplifier is realized by using pHEMT and microstrip line, shows 66% power added efficiency (PAE) at 2.4GHz with 17.6dBm output power. With -3dBm input power of wireless LAN, measured output spec01m can meet the required IEEE 802.11g standard spectrum mask. That means the required amplifier back off of 9dB from $P_{ldB}$ to satisfy the required wireless LAN spectrum mask.

• International Journal of Computer Science & Network Security
• /
• v.23 no.4
• /
• pp.172-178
• /
• 2023

When the mobile device moves from the coverage of one access point to the radio coverage of another access point it needs to maintain its connection with the current access point before it successfully discovers the new access point, this process is known as handoff. During handoff the acceptable delay a voice over IP application can bear is of 50ms whereas the delay on medium access control layer is high enough that goes up to 350-500ms. This research provides a suitable methodology on medium access control layer of the IEEE 802.11 network. The medium access control layer comprises of three phases, namely discovery, reauthentication and re-association. The discovery phase on medium access control layer takes up to 90% of the total handoff latency. The objective is to effectively reduce the delay for discovery phase to ensure a seamless handoff. The research proposes a scheme that reduces the handoff latency effectively by scanning channels prior to the actual handoff process starts and scans only the neighboring access points. Further, the proposed scheme enables the mobile device to scan first the channel on which it is currently operating so that the mobile device has to perform minimum number of channel switches. The results show that the mobile device finds out the new potential access point prior to the handoff execution hence the delay during discovery of a new access point is minimized effectively.

• Proceedings of the KIEE Conference
• /
• 2004.11c
• /
• pp.237-239
• /
• 2004

Wireless LAN Voice over IP(VoIP) equipment needs Quality-of-Service(QoS) with priority for processing real-time traffic. This paper shows transmit function implementation of wireless LAN(WLANs) media access control(MAC) support VoIP, and it has an advantage of guarantee of QoS and is adaptable to VoIP or mobile wireless equipment. The IEEE 802.11e standard in progress has four queues according to four access categories(AC) for transmit and the MAC transmits the data based on EDCA. The value of AC is from AC0 to AC3 and AC3 has the highest priority. The transmit method implemented at this paper ensure QoS using one transmit FIFO in hardware since real-time traffic data and non real-time traffic data has the different priority. The device driver classifies real-time data and non real-time data and transmit data to hardware with information about data type. The hardware conducts shorter backoff and selects faster AIFS slot for real-time data than it for non real-time data. Therefor It make give the real-time traffic data faster channel access chance than non real-time data and enhances QoS.