• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.6 s.324
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• pp.25-31
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• 2004

fireless LAN can offer high data rate communication between wireless terminals. In IEEE 802.11 wireless LAN, a basic service unit is called a Basic Service Set (BSS), which consists of one AP and more than one wireless terminals. Terminals far from the AP may not communicate with high data rate because signal strength is weakened as they move away from the AP. In this paper we propose a method to permit high speed data transmission by grouping terminals and by using part of wireless terminals as repeaters. We analyze the proposed and algorithm via simulations. Our proposed grouping mechanism is shown to be an effective way to increase the distance for high rate transmission.

• The KIPS Transactions:PartC
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• v.12C no.3 s.99
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• pp.387-394
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• 2005

Every MAC (Medium Access Control) sub-layers of IEEE 802.11x, including IEEE 802.11e, defines Connection-based and CF (Contention Free)-based service functions in common. In this paper, a New-CF method is proposed. In the proposed method, conventional Round Robin method, which is used as a polling method by IEEE 802.11x PCF (Point Coordination Function) or IEE 802.11e HCCA, is modified to give weights to channels with heavier traffic load and to provide those weighted channels with more services. Based on NS-2 simulations, it is verified the proposed method shows better throughput in general, particularly under unbalanced traffic load conditions.

• The KIPS Transactions:PartC
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• v.17C no.6
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• pp.485-490
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• 2010

IEEE 802.11n supports two frame aggregation schemes, aggregation for MAC service data unit (A-MSDU) and aggregation for MAC protocol data unit (A-MPDU), to improve throughput at the MAC layer. In this paper, we propose a cooperative frame aggregation (CoFA), which can recover erroneous frames in a cooperative manner based on A-MPDU. Specifically, CoFA receive multiple frames from direct and relay paths, and combined multiple frames jointly. Numerical results show that CoFA outperforms direct transmission and relay transmission over diverse channel conditions.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.43 no.11 s.353
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• pp.77-82
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• 2006

Analog channel selection filter is described which is designed for a direct-conversion receiver of a IEEE 802.11a wireless LAN. The channel selection filter is an active-RC fifth-order Chebyshev filter with 10MHz cut-off frequency. Two-stage operational amplifier of the filter employs a current re-using feedforward frequency compensation scheme to minimize the power consumption. The filter has been implemented in a 0.18mm CMOS technology and the experimental results show 20mW power consumption with 1.8V supply voltage and 19dB out-of-band iIP3.

• 한국ITS학회:학술대회논문집
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• 2010.05a
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• pp.56-60
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• 2010

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.43 no.9 s.351
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• pp.17-22
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• 2006

CMOS LC VCO with fast response adaptive frequency calibration (AFC) technique for IEEE 802.11a/b/g WLANs is designed in 1.8V $0.18{\mu}m$ CMOS process. The possible operation is verified for 5.8GHz band, 5.2GHz band, and 2.4GHz band using the switchable L-C resonators. To linearize its frequency-voltage gain (Kvco), optimized multiple MOS varactor biasing tecknique is used. In order to operate in each band frequency range with reduced VCO gain, 4-bit digitally controlled switched- capacitor bank is used and a wide-range digital logic quadricorrelator (WDLQ) is implemented for fast frequency detector.

• Journal of Satellite, Information and Communications
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• v.10 no.3
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• pp.53-56
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• 2015

In this paper, we want provide improved services with faster transmission, IEEE 802.11n was standardized. A-MPDU (Aggregation MAC Protocol Data UNIT) is a vital function of the IEEE 802.11n standard, which was proposed to improve transmission rate by reducing frame transmission overhead. In this paper, we show the problems of TCP retransmission with A-MPDU and propose a solution utilizing the property of TCP cumulative ACK. If the transmission of an MPDU subframe fails, A-MPDU mechanism allows selective re-transmission of failed MPDU subframe in the MAC layer. In TCP traffic transmission, however, a failed MPDU transmission causes TCP Duplicate ACK, which causes unnecessary TCP re-transmission. Furthermore, congestion control of TCP causes reduction in throughput. By supressing unnecessary duplicate ACKs the proposed mechanism reduces the overhead in transmitting redundant TCP ACKs, and transmitting only a HS-ACK with the highest sequence number. By using the RACK mechanism, through the simulation results, it was conrmed that the RACK mechanism increases up to 20% compared the conventional A-MPDU, at the same time, it tightly assures the fairness among TCP flows.

• Journal of KIISE:Information Networking
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• v.37 no.5
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• pp.386-395
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• 2010

Widespread deployment of infrastructure WLANs has made Wi-Fi an integral part of today's Internet access technology. Despite its crucial role in affecting end-to-end performance, past research has focused on MAC protocol enhancement, analysis, and simulation-based performance evaluation without sufficiently considering a misbehavior stemming from capture effect. It is well known that the capture effect occurs frequently in wireless environment and incurs throughput unfairness between nodes. In this paper, we propose a novel Fair MAC algorithm which achieves fairness even under physically unfair environment. While satisfying the fairness, the proposed algorithm maximizes the system throughput. Extensive simulation results show that the proposed Fair MAC algorithm substantially improves fairness without throughput reduction.

• Proceedings of the KAIS Fall Conference
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• 2008.05a
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• pp.108-110
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• 2008

최근 무선 통신 기술의 발달은 장비를 간편화 하고 편리화 시키게 되었다. 또한 다양한 서비스를 창출 할 수 있는 기반이 마련하였다. 하지만 무선 랜의 다양한 서비스와 접속성의 확대는 보안의 취약점을 야기 시켰다. 본 논문에서는 IEEE802.11 무선 랜 서비스를 통하여 PDA 상에서 AP의 정보를 받아 무선 랜 보안 서비스의 특성과 취약성을 살펴보고 PDA 기반 위치 추적 시스템을 구현을 하였다.

• Journal of Digital Contents Society
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• v.15 no.3
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• pp.319-326
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• 2014

IEEE 802.11 WLAN uses CSMA/CA(Carrier Sense Multiple Access/Collision Avoidance) method in MAC(Media Access Control) protocol, and through the carrier sense checks whether other users use the channel during the data transmission to avoid the data collision. Currently, IEEE 802.11 standard recommends the use of a fixed threshold which gives an impact on carrier sensing range. However, the existing scheme using the fixed threshold causes the operation of network to be inefficiency owing to the mobility in MANET(Mobile Ad hoc NETwork). In this paper, we found the better network throughput to be obtained by applying the proposed scheme, which chooses properly the carrier sensing threshold and transmission rate considering SINR(Signal to Interference-plus-Noise Ratio), to the MANET.