• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.10 s.340
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• pp.39-50
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• 2005

In this paper, we propose a performance improving MAC algerian for the IEEE 802.11 DCF. WLAN based IEEE 802.11 uses two control methods called 'Distributed Coordination Function(UF)' and 'Point Coordination Function(PCF)'. The nF controls the Urnsmission based on carrier sense multiple access with collision detection(CSMA/CA), that decides a random backoff time with the range of contention window for each terminal. Normally, each terminal the CW double after collision, and reduces the CW to the minimum after successful transmission. This paper proposes an enhanced DCF algorithm that decreases the CW smoothly after successful transmission in order to reduce the collision Probability by utilizing the current status information of WLAN. We also analyze the throughput and delay performance for the unsaturated case mathematically. Simulation results show that our algorithm enhances the saturation throughput of WLAN. They also coincide well with the analytical results.

• Journal of Digital Convergence
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• v.12 no.10
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• pp.317-327
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• 2014

To improve the efficiency of wireless channel, IEEE 802.11ac uses the DL MU-MIMO MAC scheme through which an AP transmits multiple frames to different mobile nodes simultaneously. IEEE 802.11ac DL MU-MIMO MAC needs a new step, called as TXOP sharing, between legacy IEEE 802.11n DL SU-MIMO's two operations, the obtaining an EDCA TXOP and the transmitting multiple frames for EDCA TXOP. In the TXOP sharing operation, both wireless channel destinations and frames transmitted for its TXOP period should are determined. So this paper deals with the TXOP sharing for improving IEEE 802.11ac MAC performance. However, the EDCA priority based method mentioned by IEEE 802.11ac standard document not fair among the buffers and the frames of buffers, and occurs in high_loss rate and high_delay about specific buffers. In this paper, we propose a new scheme of the TXOP sharing with sequencing p-AC, s-AC in similar properties, and all S-AC. This method provides a differentiated service without damage of EDCA characteristics.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.6
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• pp.263-268
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• 2010

As the demand of high quality service in next generation wireless communication systems, a high performance of data transmission requires an increase of spectrum efficiency and an improvement of error performance in wireless communication systems. In this paper, we propose a multi-user multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system with cyclic delay diversity and block diagonalization procoding method to improve bit error rate (BER) performance with wireless local area network (WLAN) channel model C and D for 802.11n WLAN system. The results of mathlab simulation show the improvement of BER performance in 802.11n wireless indoor channel environment.

• JSTS:Journal of Semiconductor Technology and Science
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• v.15 no.2
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• pp.280-285
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• 2015

A fully integrated high-efficiency linear CMOS power amplifier (PA) is developed for 802.11n WLAN applications using the 65-nm standard CMOS technology. The transformer topology is investigated to obtain a high-efficiency and high-linearity performance. By adopting a 2:2 output transformer, an optimum impedance is provided to the PA core. Besides, a LC harmonic control block is added to reduce the AM-to-AM/AM-to-PM distortions. The CMOS PA produces a saturated power of 26.1 dBm with a peak power-added efficiency (PAE) of 38.2%. The PA is tested using an 802.11n signal, and it satisfies the stringent error vector magnitude (EVM) and mask requirements. It achieves -28-dB EVM at an output power of 18.6 dBm with a PAE of 14.7%.

• Journal of Broadcast Engineering
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• v.20 no.2
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• pp.300-309
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• 2015

In IEEE 802.11n WLANs(Wireless Local Area Networks), to support high throughput, MAC(Media Access Control) layer adopts A-MSDU(Aggregate-MAC Service Data Unit) and A-MPDU(Aggregate-MAC Protocol Data Unit). Generally, as the A-MPDU uses a selective retransmission capability, A-MPDU provides higher throughput than A-MSDU. However, although A-MPDU uses the selective re-transmission capability, if the size of MPDU within A-MPDU is smaller than the size of minimum MPDU starting spacing, A-MPDU can reduce throughput because of the overhead of retransmission owing to the addition of delimiter, that is a dummy MPDU. Therefore, to overcome the above problem, two-level Aggregation method, where the small MPDU within A-MPDU is replaced by not delimiter but A-MSDU, has been introduced. In the two-level Aggregation method, the existing re-transmission scheme retransmits only A-MPDU, but if the size of retransmission data is smaller than the size of the minimum MPDU starting spacing, the proposed retransmission scheme retransmits the aggregated retransmission data and MSDUs. Therefore, we know that the proposed retransmission scheme have better throughput that the existing retransmission scheme.

• Information and Communications Magazine
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• v.28 no.11
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• pp.56-65
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• 2011

가정, 기업, 오피스 및 공공장소에서의 폭넓은 무선 데이터 서비스 사용에 따라 거대한 영향력과 시장성을 갖게 될 차세대 WLAN 기술 및 시스템에 대한 관심이 더욱 높아지고 있다. 본고에서는 IEEE 802.11의 표준 기술 및 표준화 진행 중인 개발 기술들에 대해 살펴본다. WLAN을 기반으로 하는 IEEE 802.11의 간략한 history와 배경뿐만 아니라, IEEE 802.11a/b/g/n/ac/ad 등의 기술적인 부분을 요약하여 개발 현황을 알아보고, 확보된 기술을 통한 시장 상태와 차세대 기술개발을 통한 시장동향을 논의한다.

• Journal of Computing Science and Engineering
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• v.8 no.2
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• pp.107-118
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• 2014

One interesting problem regarding wireless local area network (WLAN) ad-hoc networks is the effective mitigation of hidden nodes. The WLAN standard IEEE 802.11 provides request to send/clear to send (RTS/CTS) as mitigation for the hidden node problem; however, this causes the exposed node problem. The first 802.11 standard provided only two transmission rates, 1 and 2 Mbps, and control frames, such as RTS/CTS assumed to be sent at 1 Mbps. The 802.11 standard has been enhanced several times since then and now it supports multi-rate transmission up to 65 Mbps in the currently popular 802.11n (20 MHz channel, single stream with long guard interval). As a result, the difference in transmission rates and coverages between the data frame and control frame can be very large. However adjusting the RTS/CTS transmission rate to optimize network throughput has not been well investigated. In this paper, we propose a method to decrease the number of exposed nodes by increasing the RTS transmission rate to decrease RTS coverage. Our proposed method, Asymmetric Range by Multi-Rate Control (ARMRC), can decrease or even completely eliminate exposed nodes and improve the entire network throughput. Experimental results by simulation show that the network throughput in the proposed method is higher by 20% to 50% under certain conditions, and the proposed method is found to be effective in equalizing dispersion of throughput among nodes.

• Proceedings of the Korea Information Processing Society Conference
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• 2007.05a
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• pp.1294-1296
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• 2007

The IEEE 802.11 DCF forces neighboring nodes of an active transmitter to switch into inactive state. This conservative nature brings frame latency at transmitter neighborhood. This work exploits the IEEE 802.11n Frame Aggregation scheme to allow simultaneous transmissions from nodes that are neighbors to each-other. This is accomplished by the synchronization of control and data transmissions in slots of fixed length. Proposed scheme reduces the frame latency and improves aggregated network throughput.

• Korean Journal of Crystallography
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• v.2 no.1
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• pp.12-16
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• 1991

C18H22N4OS, Mr=342.47, monoclinic, P2₁/c,a=11.802(2), b=31.962(2), c=9.829(2)A, β=100.12(1)˚, V=3694.8A3,F(000)=1472, Z=8, Dx=1.246 Mg m-3, Dm=1.17Mg m-3,λ=0.71073 A, μ=0.15mm-1, T=294 K. final R=0.0856 for 3718 observed reflection (Fo>3σ(Fo)) There are two molecules in an asymmetric unit and a major difference between these molecules is in the C(9)-N(1)-C(6)-C(7) torsion angles [58.8(8)˚and 1(1)˚]. Both molecules have intramolecular N(1)-H(10)'N(3) hydrogen bonds [ 2.613(7) and 2.566(7) A] and assume V-shaped conformation with N(2) atoms at the verices. The two independent molecules are linked by the two N(2)-H(11)'S' hydrogen bonds[3.367(5) A and 3.421(4)A] and the dimergen are held together by van der Waals forces.

• Proceedings of the Korea Institutes of Information Security and Cryptology Conference
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• 2006.06a
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• pp.390-393
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• 2006

IEEE 802.11e 과 IEEE 802.11n에서 data의 높은 전송률을 구현하기 위해 Block Ack와 frame agegation 과 같은 새로운 mechanism이 논의 되고 있다. 이러한 mechanism은 각각의 MPDU processing 마다 짧은 응답시간을 요구한다. 본 논문에서는 위의 새로운 MAC을 지원하는 IEEE 802.11i를 위한 효율적인 CCMP 설계를 제안한다. 제안된 설계에서는 한 AES-CCM core에서 MIC calculation 과 정보 암호화가 128bit씩 순차적으로 수행되어지는 mode toggling 접근을 채택했다. 본 설계에서는 응답시간이 44 clock cycle의 짧은 짧은 시간으로 줄었다. 또한 하나의 AES-CCM core를 사용하고 낮은 주파수에서 수용할만한 data throughput과 응답시간을 얻었기 때문에 하드웨어적인 복잡성과 전력 소모를 줄일수 있었다.