• Title/Summary/Keyword: back-off based random access

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Backoff-based random access algorithm for offering differentiated QoS services in the random access channels of OFDMA systems (OFDMA 시스템 상향 링크에서, 임의 접근 채널의 차별화된 서비스 품질 제공을 위한 Backoff 기반 임의 접근 알고리즘 및 그 성능 분석)

  • Lee, Young-Du;Koo, In-Soo
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.12 no.2
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    • pp.360-368
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    • 2008
  • In this paper, in order that the various QoS(Qualify of Service)s that are required by different traffic class are guaranteed in the random access channels in multi-service multi-user OFDMA systems, the backoff-based random access algorithm is proposed and corresponding performance is analyzed in terms of the access success probability, the throughput, the average delay and the blocking probability. Through the numerical analysis, it is shown that the proposed backoff-based random access algorithm can provide the differentiated QoSs to random access attempts according to their service class.

An Enhanced Message Priority Mechanism in IEEE 802.11p Based Vehicular Networks

  • Liu, Chang;Chung, Sang-Hwa;Jeong, Han-You;Jung, Ik-Joo
    • Journal of Information Processing Systems
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    • v.11 no.3
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    • pp.465-482
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    • 2015
  • IEEE 802.11p is a standard MAC protocol for wireless access in vehicular environments (WAVEs). If a packet collision happens when a safety message is sent out, IEEE 802.11p chooses a random back-off counter value in a fixed-size contention window. However, depending on the random choice of back-off counter value, it is still possible that less important messages are sent out first while more important messages are delayed longer until sent out. In this paper, we present a new scheme for safety message scheduling, called the enhanced message priority mechanism (EMPM). It consists of the following two components: the benefit-value algorithm, which calculates the priority of the messages depending on the speed, deceleration, and message lifetime; and the back-off counter selection algorithm, which chooses the non-uniform back-off counter value in order to reduce the collision probability and to enhance the throughput of the highly beneficial messages. Numerical results show that the EMPM can significantly improve the throughput and delay of messages with high benefits when compared with existing MAC protocols. Consequently, the EMPM can provide better QoS support for the more important and urgent messages.

WLAN OFDMA Random Access Based Communications for In-Aircraft Wireless Sensor Networks (비행체 무선 센서망을 위한 무선랜 OFDMA 임의접근 기반 통신)

  • Ahn, Woojin;Kim, Ronny Yongho
    • Journal of Advanced Navigation Technology
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    • v.20 no.3
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    • pp.252-257
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    • 2016
  • In this paper a novel access scheme for uplink multiuser transmission based on IEEE 802.11ax random access in in-aircraft wireless sensor networks is proposed. The proposed scheme provides an efficient access control mechanism with three divisions of OFDMA backoff counter (OBO): access, deferring, dropping, which controls the number of potential uplink transmission stations. The proposed scheme can be used efficiently in in-aircraft wireless sensor network where a large number of sensors need to be supported. By using the proposed scheme, since in-aircraft sensors attempt channel access using the proposed differentiated OBO parameters, the number of stations exceeds the access capacity can be efficiently controlled. This paper also provides the mathematical analysis of the proposed scheme, regarding the optimal parameters. According to the performance analysis, the proposed scheme is able to efficiently control the access behavior of wireless sensors in the network.

Distributed CSMA/CA Medium Access Control for Incomplete Medium Sharing Systems with General Channel Access Constraints (불완전매체공유 환경을 위한 CSMA/CA기반 분산방식 매체접근제어기법)

  • Lee Byoung-Seok;Jeon Byoung-Wook;Choe Jin-Woo
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.31 no.5B
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    • pp.365-377
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    • 2006
  • We define the incomplete medium sharing system as a multi-channel shared medium communication system where any types of constraints are imposed to the set of channels that may be allocated to any transmitter-receiver node pair. A set of distributed MAC schemes are proposed, all of which are based on the CSMA/CA scheme employed in IEEE 802. 11 WLAN standards. Distributed MAC schemes are proposed in three different forms, which can be differentiated by the number and the location of back-off timers; that is, (1) one timer for all queues destined for different receiver nodes, (2) multiple timers at individual transmission queues, (3) multiple timers for individual channels. Through an extensive set of computer simulations, the performances of the proposed MAC schemes show that the MAC scheme with timers at individual transmission queues outperform the others in terms of throughput and delay for most cases considered. The complexity of the proposed schemes is also compared, and the first scheme obviously turned out to be the simplest, and the complexity of the second and third schemes depends on the number of receiver nodes and the number of channels, respectively.