• Journal of Communications and Networks
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• 제11권2호
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• pp.175-186
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• 2009

A new medium access control (MAC) scheme embedding physical channels into multiband carrier sense multiple access/collision avoidance (CSMA/CA) networks is proposed to provide strict quality of service (QoS) guarantee to high priority users. In the proposed scheme, two priority classes of users, primary and secondary users, are supported. For primary users physical channels are provided to ensure strict QoS, whereas secondary users are provided with best-effort service using CSMA/CA modified for multiband operation. The performance of the proposed MAC scheme is investigated using a new multiband CSMA/CA Markov chain model capturing the primary user activity and the operation of secondary users in multiple bands. The throughput of secondary users is obtained as a function of the primary user activity and other CSMA/CA parameters. It is shown that the new MAC scheme yields larger throughput than the conventional single-band CSMA/CA when both schemes use the same bandwidth.

• 한국항행학회논문지
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• 제7권2호
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• pp.199-205
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• 2003

본 논문에선 플래그를 이용한 전송시의 충돌 완화 및 재전송 슬롯 선택 방식의 변형을 통하여 CSMA/CA(Carrier Sensing Multiple Access/Collision Avoidance) 프로토콜을 항공용 VHF통신에 적합하게 변형시켰다. 일반적으로 CSMA/CA 프로세스는 경쟁 서비스에서 충돌이 일어났을 때 재전송 지연시간만큼 기다리게 되고 경쟁윈도우의 크기가 2배로 커진다. 이로 인해 부하가 증가하면 지연시간이 커지고 처리량이 감소한다. 이를 해결하기 위해 본 논문에서는 충돌 플래그를 이용하여 본래의 경쟁 윈도우의 크기 변화과정을 변형시켰으며 CSMA/CA 전체 상태 천이 과정에서 충돌시의 과정을 단축시켰다. 또한 패킷이 생성된 상태에서 충돌이 일어나면 플래그를 이용하여 초기에 증가된 경쟁윈도우를 갖고 Backoff 모드에 진입함으로써 재충돌 확률을 줄였다. 시뮬레이션을 수행한 결과 부하가 증가하여도 처리량 및 지연 시간에 대해 좋은 특성을 나타냈으며 제안된 프로토콜은 항공용 VHF 통신에 적합함을 확인하였다.

• 한국정보통신학회논문지
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• 제3권1호
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• pp.75-82
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• 1999

무선 실시간 모니터링 시스템은 무선 모뎀, 중앙 모니터, 이동단말기, 데이터베이스 서버로 구성되며 환자의 이동성, 설치시간의 감소, 장기간으로 본 비용절감 등의 잇점을 제공한다. 또한 이 시스템은 환자 위치추적 서비스를 제공한다. 환자 위치 추적 서비스는 무선 모니터링 시스템의 경우 환자 이동중 위급 상황 발생시 응급 처치를 위해 반드시 제공되어야 한다. 본 논문에서는 개선된 CSMA/CA프로토콜과 환자 위치 추적 알고리즘을 제안하고 이를 이용하여 무선 실시간 모니터링 시스템을 구현하였다.

• Journal of Communications and Networks
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• 제6권3호
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• pp.226-234
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• 2004

This work presents a deterministic channel that rules according to inverse a power propagation law. The proposed channel model allows us to derive the lower bound and upper bound of packet's capture probability in Rayleigh fading and shadowing cellular mobile system. According to these capture probabilities, we analyze the system performance in the case of finite stations and finite communicated coverage of a base station. We also adopted a dynamic backoff window size to discuss the robustness of IEEE 802.11 draft standard. Some suggestions and conclusions from numerical results are given to establish the more strong CSMA/CA protocol.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2003년도 하계종합학술대회 논문집 I
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• pp.49-52
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• 2003

IEEE 802.11 MAC uses a distributed coordination function (DCF) known as carrier sense multiple access with collision avoidance (CSMA/CA) for medium access. Random back-off algorithm helps to avoid the collision. This paper proposes virtual back-off and modified back-off algorithm for reduce a waiting time by back-off and reduce the collision. The modified DCF is consisted of these two algorithms. We expect to reduce the average waiting time of each transmission by using the modified DCF algorithm.

• 인터넷정보학회논문지
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• 제13권1호
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• pp.7-14
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• 2012

본 논문은 불완전한 채널 감지를 고려한 포화 상태에서의 IEEE 802.11 carrier-sense multiple access with collision-avoidance(CSMA/CA)의 성능을 분석한다. 불완전한 채널 감지는 missed-detection과 false alarm을 포함하는데, 이러한 불완전한 채널 감지가 IEEE 802.11의 성능에 미치는 영향을 분석하고 이를 수식적으로 표현한다. 물리 계층의 불완전한 채널 감지를 표현하기 위해, 본 논문에서는 기존의 2차원 마코프 프로세스 모델을 수정했다. 모의실험 결과와 제안된 모델의 이론적인 결과가 일치하는 것을 보였다. 이러한 실험 결과를 바탕으로, 감지 확률이 IEEE 802.11의 성능에 있어 가장 중요한 요소임을 확인하였다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2003년도 통신소사이어티 추계학술대회논문집
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• pp.191-194
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• 2003

In IEEE 802.11b, Medium Access Control Sublayer consists of DCF (Distributed Coordination Function) and PCF (Point Coordination Function). DCF provides contention based services and PCF provides contention free services for QoS satisfaction. DCF uses CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) as an access protocol. And PCF uses Polling Scheme. In this paper, a modified New-PCF, which gives weights to channels with heavier traffic load, was suggested. NS-2 simulations were conducted to compare the service performances with original DCF, PCF and the modified New-PCF respectively. Simulation results has shown the increased overall throughput with the proposed New-PCF compared with other cases.

• 전자공학회논문지S
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• 제34S권12호
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• pp.50-59
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• 1997

A wireless LAN medical information transmission system is useful for patients who need mobility in a local area environment. This paper proposes a method using WLAN(wireless local area network) and implements a stand-alone system with MAC(meidum access control) layer protocol referenced IEEE 802.11 draft standard. The system consists of a 8bit-microprocessor which handles media access control protocol and a WL100(GEC Plessey) chip which takes care of phsical layer specific routines and uses a RF module DE6003(GEC Plessey). The major features of the implemented system are the CSMA/CA protocol used a consecutive DATA-ACK trasmission method which yields more effective bandwidth allocation for asyncronous traffic transmission and the modified PCF protocol for time-bounded traffic transmission, which operates in ad-hoc network topology apart from IEEE 802.11 draft standard confirm PCF mode operate in infrastruture topology.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권4호
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• pp.989-1005
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• 2012

In this paper, throughput of IEEE 802.11 carrier-sense multiple access (CSMA) with collision-avoidance (CA) protocols in non-saturated traffic conditions is presented taking into account the impact of imperfect channel sensing. The imperfect channel sensing includes both missed-detection and false alarm and their impact on the utilization of IEEE 802.11 analyzed and expressed as a closed form. To include the imperfect channel sensing at the physical layer, we modified the state transition probabilities of well-known two state Markov process model. Simulation results closely match the theoretical expressions confirming the effectiveness of the proposed model. Based on both theoretical and simulated results, the choice of the best probability detection while maintaining probability of false alarm is less than 0.5 is a key factor for maximizing utilization of IEEE 802.11.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권9호
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• pp.4242-4263
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• 2017

Multi-User Multiple-Input Multiple-Output (MU-MIMO) technology has recently attracted significant attention from academia and industry because of it is increasingly important role in improving networks' capacity and data rate. Moreover, MU-MIMO systems for the Fifth Generation (5G) have already been researched. High Quality of Service (QoS) and efficient operations at the Medium Access Control (MAC) layer have become key requirements. In this paper, we propose a downlink MU-MIMO MAC protocol based on adaptive Channel State Information (CSI) feedback (called MMM-A) for Wireless Local Area Networks (WLANs). A modified CSMA/CA mechanism using new frame formats is adopted in the proposed protocol. Specifically, the CSI is exchanged between stations (STAs) in an adaptive way, and a packet selection strategy which can guarantee a fairer QoS for scenarios with differentiated traffic is also included in the MMM-A protocol. We then derive the expressions of the throughput and access delay, and analyze the performance of the protocol. It is easy to find that the MMM-A protocol outperforms the commonly used protocols in terms of the saturated throughput and access delay through simulation and analysis results.