An Adaptive Contention Windows Adjustment Scheme Based on the Access Category for OnBord-Unit in IEEE 802.11p

IEEE 802.11p에서 차량단말기간에 혼잡상황 해결을 위한 동적 충돌 윈도우 향상 기법

  • Received : 2010.09.23
  • Published : 2010.11.25

Abstract

The study aims at offering a solution to the problems of transmission delay and data throughput decrease as the number of contending On-Board Units (OBU) increases by applying CSMA medium access control protocol based upon IEEE 802.11p. In a competition-based medium, contention probability becomes high as OBU increases. In order to improve the performance of this medium access layer, the author proposes EDCA which a adaptive adjustment of the Contention Windows (CW) considering traffic density and data type. EDCA applies fixed values of Minimum Contention Window (CWmin) and Maximum Contention Window (CWmax) for each of four kinds of Access Categories (AC) for channel-specific service differentiation. EDCA does not guarantee the channel-specific features and network state whereas it guarantees inter-AC differentiation by classifying into traffic features. Thus it is not possible to actively respond to a contention caused by network congestion occurring in a short moment in channel. As a solution, CWminAS(CWmin Adaptation Scheme) and ACATICT(Adaptive Contention window Adjustment Technique based on Individual Class Traffic) are proposed as active CW control techniques. In previous researches, the contention probabilities for each value of AC were not examined or a single channel based AC value was considered. And the channel-specific demands of IEEE 802.11p and the corresponding contention probabilities were not reflected in the studies. The study considers the collision number of a previous service section and the current network congestion proposes a dynamic control technique ACCW(Adaptive Control of Contention windows in considering the WAVE situation) for CW of the next channel.

본 논문은 IEEE 802.11p에 기반한 CSMA의 미디어 접근 제어로서, 경쟁 차량단말기(OnBord Unit, OBU)의 증가에 따른 전송 지연(transmission delay)과 감소(data throughput decrease) 문제를 해결하고자 한다. 경쟁 기반의 전송매체에서는 OBU 증가에 따라 충돌 확률이 높아진다. 이러한 미디엄 계층의 성능 향상을 위해 교통량과 데이터 종류를 고려하여 접속 단말기의 개별 충돌 윈도(Contention Windows, CW)를 동적으로 조절하는 EDCA(Enhanced Distributed Channel Access)를 제안하였다. EDCA는 채널별 서비스 차별화를 위해 네 개의 클래스를 AC(Access Category)마다 고정된 최소 경쟁 윈도우(CWmin) 값과 최대 경쟁 윈도우(CWmax) 값을 적용한다. EDCA는 트래픽 특성별로 구분되어 AC 간의 차별화를 보장하지만, IEEE 802.11p 에 구성된 채널별 특성과 네트워크 상태를 보장하지 않기 때문에, 짧은 채널 서비스별 혼잡에 따른 충돌 발생을 능동적으로 대처할 수 없다. 이에 따른 해결방안으로 CWminAS(CWmin Adaptation Scheme)와 ACATICT(Adaptive Contention window Adjustment Technique based on Individual Class Traffic)가 능동적인 CW의 제어 기법으로 제시되었다. 선행연구는 개별 AC 값에 따라 발생하는 충돌 확률을 고려하지 않거나 단일 채널 기반의 개별 AC 값만 고려하고, IEEE 802.11p의 채널별 요구 사항과 이에 따른 충돌 확률을 반영하지 않았다. 본 연구는 이전 서비스 구간에서 OBU 경쟁에 따라 발생하는 충돌 횟수와 현재 무선망의 혼잡을 고려하여, 다음 채널의 CW를 능동적으로 제어하는 기법으로 ACCW(Adaptive Control of Contention windows in considering the WAVE situation)를 제안한다.

Keywords

References

  1. IEEE Std 802.11e, "Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications; Amendment: Medium Access Control(MAC) Quality of Service Enhancements," IEEE Std 802.11e-2005, November 2005.
  2. Lassaad Gannoune and Stephan Robert. "Dynamic Tuning of the Contention Window Minimum (CWmin) for Enhanced Service Differentiation in IEEE 802.11 Wireless Ad-Hoc Networks," IEEE PIMRC 2004
  3. Vasilios A. Siris, George Stamatakis, "Optimal CWmin Selection for Achieving Proportional Fairness in Multi-Rate 802.11e WLANs: Test-bed Implementation and Evaluation," WiNTECH''06.
  4. Romdhani, L., Qiang Ni, Turletti, T., "Adaptive edcf: enhanced service differentiation for IEEE 802.11 wireless ad-hoc networks," WCNC 2003, Vol. 2, Mar. 2003.
  5. IEEE Computer Society, IEEE P802.11pTM/ D5.0, Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications, 2008.
  6. Osamu Maeshima, et al. ,"A roadside to vehicle communication system for vehicle safety using dual frequency channels," IEIC Technical Report, Vol 106, No. 265, pp. 13-18, 2006
  7. IEEE Vehicular Technology Society, IEEE std 1609.4; IEEE Trial-Use Standard for Wireless Access in Vehicular Environments (WAVE)- Multi-channel Operation[online], 2006.
  8. 엄진영, 오경식, 안종석, "802.11e의 성능 향상을 위한 개별적 클래스 트래픽에 기반한 동적 충돌윈도우 크기 조절 기법," 정보과학회 제 14권, 제4호. 2008년 4월
  9. Katrin Bilstrup, ect. "Does the 802.11p MAC Method Provide Predictable Support for Low Delay Commuincation" ETSI workshop on ITS, February 2009.
  10. Jacob J. Meyers, "Channel Characterization and Reliability of 5.8 GHz DSRC Wireless Communication Links in Vehicular Ad Hoc Networks in Suburban Driving Environment," Carnegie Mellon University, October 2005,
  11. J. A. Olivera, I. Cortázar, C. Pinart, A. Los Santos, I. Lequerica, "VANBA: a simple handover mechanism for transparent, always-on V2V communications", in Proc. IEEE 69th Vehicular Technology Conference (VTC2009- Spring). Barcelona (Spain), April 26-29, 2009.
  12. Communication for eSafety, "D31 Europena ITS Communication Architecture v2.0.02," http:// www.come-safety.org/COMeSafety_EL_D31 _EuropeanITSCommunicationArchitecture_v2.0_02. pdf
  13. Eunjun Choi, Wonjun Lee and Timothy K. Shih, "Traffic Flow based EDCF for QoS Enhancement in IEEE 802.11e Wireless LAN," AIAN '07(Canada), May 21-23, pp. 467-473, 2007.
  14. A. Naffa, A. Ksentini, and A. Mehaoua, "Sliding Contention Window (SCW): Towards Backoff Range-Based Service Differentiation over IEEE 802.11 Wireless LAN Networks," IEEE Network'05, vol. 19, pp. 45-51, July 2005. https://doi.org/10.1109/MNET.2005.1470682