• Proceedings of the Korea Contents Association Conference
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• 2008.05a
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• pp.564-568
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• 2008

In this paper, MAC(Medium Access Control) algorithm for the IEEE 802.11 DCF(Distributed Coordination Function) improving the performance is proposed and analyzed mathematically. The MAC of IEEE 802.11 WLAN to control data transmission uses two control methods called DCF and PCF(Point Coordination Function). The DCF controls the transmission based on CSMA/CA(Carrier Sense Multiple Access with Collision Avoidance). The DCF shows excellent performance relatively in situation that competition station is less but has a problem that performance is fallen from throughput and delay viewpoint in situation that competition station is increased. This paper proposes an enhanced DCF algorithm that increases the CW to maximal CW after collision and decreases the CW smoothly after successful transmission in order to reduce the collision probability by utilizing the current status information of WLAN. To prove efficiency of proposed algorithm, a lots of simulations are conducted and analyzed.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.8
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• pp.1589-1595
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• 2007

Recently many communication systems ate adapting the OFDM(Orthogonal Frequency Division Multiplexing) for multimedia data services. However, OFDM has some problems that PAPR is increased when sub-carries are summed up with same phases. This problem causes severe signal distortions while the signal is passing through non-linear system such as power amplifier resulting in performance degradation of transmission system. In this paper, we use IF-Clipping method to solve PAPR problem and the signal distortion caused by clipping is limited by use of SAW (Surface Acoustic Wave) filter and power amplifier(TWTA). And we derive the optimal parameter(PAPR, Backoff) values to meet the spectrum mask of WiBro system.

• Journal of the Korea Society of Computer and Information
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• v.15 no.1
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• pp.129-137
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• 2010

In this paper, we propose a packet prioritization scheme using preamble signal and backoff time which is designed to provide a differentiated channel occupation with a packet priority in wireless sensor networks. This scheme aims at enabling QoS such as fast delivery of high priority packets by reducing their backoff time as well as thus securing higher channel occupation. We expect that it could also improve the channel utilization of the entire network by avoiding unnecessary channel contention. For the purpose, we add new features of multiple queue and preamble modification to the TinyOS based B-MAC. This scheme achieves 82-88% reduction in delivery time of high priority packets, thus it enables realtime support for urgent applications.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.16 no.1
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• pp.334-349
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• 2022

The effectiveness of Wi-Fi networks is greatly influenced by the optimization of contention window (CW) parameters. Unfortunately, the conventional approach employed by IEEE 802.11 wireless networks is not scalable enough to sustain consistent performance for the increasing number of stations. Yet, it is still the default when accessing channels for single-users of 802.11 transmissions. Recently, there has been a spike in attempts to enhance network performance using a machine learning (ML) technique known as reinforcement learning (RL). Its advantage is interacting with the surrounding environment and making decisions based on its own experience. Deep RL (DRL) uses deep neural networks (DNN) to deal with more complex environments (such as continuous state spaces or actions spaces) and to get optimum rewards. As a result, we present a new approach of CW control mechanism, which is termed as contention window threshold (CW_Threshold). It uses the DRL principle to define the threshold value and learn optimal settings under various network scenarios. We demonstrate our proposed method, known as a smart exponential-threshold-linear backoff algorithm with a deep Q-learning network (SETL-DQN). The simulation results show that our proposed SETL-DQN algorithm can effectively improve the throughput and reduce the collision rates.

• 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.

• Proceedings of the Korean Information Science Society Conference
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• 2002.04a
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• pp.241-243
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• 2002

본 논문은 무선 랜 상에서 전송 지연을 보장하기 위한 백오프 방식을 제안한다. 이 방식은 전송되는 트래픽의 종류에 따라 백오프 시간을 할당하도록 설계되었으며, 기존의 IEEE 802.11 매체접근제어 방식을 그대로 유지하며, 보다 향상된 서비스 품질을 지원한다. 제안된 백오프 방식에서는 모든 트래픽을 실시간 트래픽과 비실시간 트래픽으로 구분하여 처리된다. 실시간 트래픽은 제안된 백오프 방식으로 처리되고, 비실시간 트래픽은 기존의 IEEE 802.11 방식에 의해 처리된다. 본 논문에서는 컴퓨터 시뮬레이션을 사용하여 제안된 백오프 방식을 성능 평가하였으며, 시뮬레이션 결과는 전송지연 관점에서 기존의 IEEE 802.11e 방식보다 성능이 향상됨을 보여준다.

• Proceedings of the Korea Multimedia Society Conference
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• 2003.11a
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• pp.441-444
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• 2003

본 논문에서는 CDMA S-ALOHA 시스템에서 단말기들의 공평한 패킷 전송을 보장하기 위한 중앙 집중형 백오프 기법을 제안하고 이에 대한 성능을 분석한다. 전용 코드 방식의 CDMA 시스템에서는 각 단말기들이 고유의 확산코드를 이용하여 패킷을 전송하므로 패킷 충돌로 인한 전송 실패는 없는 반면, 다원 전속 간섭에 의한 비트 오류가 패킷 전송의 실패 요인이 된다. 제안한 기법에서는 기지국이 망의 부하에 따라 단말기들의 백오프를 위한 확률을 계산하여 방송하고, 단말기에서는 이를 기반으로 패킷 전송을 시도한다.

• ETRI Journal
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• v.29 no.6
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• pp.829-831
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• 2007

This letter proposes an analytical model to characterize medium utilization in IEEE 802.11e operating in HCCA-EDCA mixed mode (HEMM). In contrast to existing works which model the backoff process in individual stations, we consider the channel occupancy pattern. Additionally, our work considers the operation of HEMM, which is not widely documented. We show that the proposed model accurately characterizes medium utilization with no more than 5% error.

• The Journal of the Acoustical Society of Korea
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• v.19 no.1E
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• pp.22-26
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• 2000

In this paper, the DS/CDMA PN code acquisition system with nonlinear transmitter power amplifier based on digital matched filter (DMF) which has the rapid acquisition time is presented and the performance is evaluated in terms of mean acquisition time, detection probability, and signal to interference under multiuser environment. The performance is presented with respect to the output backoff of the nonlinear amplifier and the correlation window.

• Proceedings of the Korea Information Processing Society Conference
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• 2016.10a
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• pp.136-137
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• 2016

WSN의 활용 분야 중 하나로 표준화된 IEEE 802.15.4 WBAN(wireless body area networks)은 웨어러블 디바이스의 무선 통신환경을 고려한 기술이다. WBAN은 높은 밀집도를 가지는 특징을 가지며, 이로 인하여 데이터 충돌이 큰 이슈가 되고 있다. 본 논문에서는 WBAN의 표준에서 제시한 메시지 우선순위를 백오프 알고리즘에 적용하여 WBAN 환경에 더 효율적인 전송을 제공하는 것을 목표로한다.