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Enhancements of IEEE 802.11p Protocol for Access Control on a VANET Control Channel University of Toulouse Institut de Recherche en Informatique de Toulouse Razvan Stanica, Emmanuel Chaput, Andr-Luc Beylot IEEE International Conference on

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Enhancements of IEEE 802.11p Protocol for Access Control on a VANET Control Channel

University of Toulouse Institut de Recherche en Informatique de Toulouse

Razvan Stanica, Emmanuel Chaput, André-Luc Beylot

IEEE International Conference on Communications Kyoto - 06 June 2011

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Enhancements of IEEE 802.11p Protocol for Access Control on a VANET Control Channel

 Safety Communication in Vehicular Networks  Congestion Control using IEEE 802.11p  Influence of the Minimum Contention Window  Decrementing Contention Window

Razvan Stanica University of Toulouse ICC 2011

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Decrementing CW

Safety V2V

Minimum CW Razvan Stanica University of Toulouse ICC 2011

VANET objective: Building an accurate image of the exterior world  Cooperative Awareness Message (CAM)  Decentralised Environmental Notification (DEN)

Congestion Control Enhancements of IEEE 802.11p Protocol for Access Control on a VANET Control Channel

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Decrementing CW

Safety V2V

Minimum CW Razvan Stanica University of Toulouse ICC 2011 Congestion Control

5.860 5.870 5.880 5.890 5.900 5.910 5.920 G5SC4 G5SC3 G5SC1 G5SC2 G5CC CH172 CH174 CH176 CH178 CH180 CH182 CH184 USA Spectrum Allocation Europe Spectrum Allocation  Service channels (SCH) – non-safety (usually IP-based) applications  Control channel (CCH) – safety applications

Enhancements of IEEE 802.11p Protocol for Access Control on a VANET Control Channel

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Decrementing CW Safety V2V Minimum CW Razvan Stanica University of Toulouse ICC 2011 Congestion Control

 Amendment to the IEEE 802.11-2007 standard  Published in June 2010  Based on an OFDM PHY at 5.9GHz  Included in both WAVE and ETSI ITS architectures  MAC layer follows the IEEE 802.11e EDCA function  STAs can communicate without belonging to the same BSS

IEEE 802.11p

Enhancements of IEEE 802.11p Protocol for Access Control on a VANET Control Channel

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Decrementing CW Safety V2V Minimum CW Razvan Stanica University of Toulouse ICC 2011 Congestion Control

Congestion Control

 Reduce Beaconing Frequency

Enhancements of IEEE 802.11p Protocol for Access Control on a VANET Control Channel

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Decrementing CW Safety V2V Minimum CW Razvan Stanica University of Toulouse ICC 2011 Congestion Control

Congestion Control

 Reduce Beaconing Frequency

Strict requirements from applications

Enhancements of IEEE 802.11p Protocol for Access Control on a VANET Control Channel

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Decrementing CW Safety V2V Minimum CW Razvan Stanica University of Toulouse ICC 2011 Congestion Control

Congestion Control

 Reduce Beaconing Frequency

Strict requirements from applications

 Decrease Transmission Power

Enhancements of IEEE 802.11p Protocol for Access Control on a VANET Control Channel

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Decrementing CW Safety V2V Minimum CW Razvan Stanica University of Toulouse ICC 2011 Congestion Control

Congestion Control

 Reduce Beaconing Frequency

Strict requirements from applications

 Decrease Transmission Power

Minimal coverage area

Enhancements of IEEE 802.11p Protocol for Access Control on a VANET Control Channel

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Decrementing CW Safety V2V Minimum CW Razvan Stanica University of Toulouse ICC 2011 Congestion Control

Congestion Control

 Reduce Beaconing Frequency

Strict requirements from applications

 Decrease Transmission Power

Minimal coverage area

 Increase Data Rate

Enhancements of IEEE 802.11p Protocol for Access Control on a VANET Control Channel

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Decrementing CW Safety V2V Minimum CW Razvan Stanica University of Toulouse ICC 2011 Congestion Control

Congestion Control

 Reduce Beaconing Frequency

Strict requirements from applications

 Decrease Transmission Power

Minimal coverage area

 Increase Data Rate

Noisy channel, reduced reception probability

Enhancements of IEEE 802.11p Protocol for Access Control on a VANET Control Channel

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Decrementing CW Safety V2V Minimum CW Razvan Stanica University of Toulouse ICC 2011 Congestion Control Enhancements of IEEE 802.11p Protocol for Access Control on a VANET Control Channel

Contention Window in unicast IEEE 802.11

 If channel free – send directly  If channel busy – back off for n idle slots  n= random (0, CW)  Initially CW= CWmin  If collision – CW= CW*2

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Decrementing CW Safety V2V Minimum CW Razvan Stanica University of Toulouse ICC 2011 Congestion Control Enhancements of IEEE 802.11p Protocol for Access Control on a VANET Control Channel

Contention Window in unicast IEEE 802.11 broadcast

 If channel free – send directly  If channel busy – back off for n idle slots  n= random (0, CW)  Initially CW= CWmin  If collision – CW= CW*2

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Decrementing CW Safety V2V Minimum CW Razvan Stanica University of Toulouse ICC 2011 Congestion Control Enhancements of IEEE 802.11p Protocol for Access Control on a VANET Control Channel CW-1 CW-2 i i-1 1 Col Rec CW-1 CW-2 i i-1 1 Col Rec CW-1 CW-2 i i-1 1 Col Rec CW-1 CW-2 i i-1 1 Col Rec CW-1 CW-2 i i-1 1 Col Rec CW-1 CW-2 i i-1 1 Col Rec

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . t=0 t=1 t=k-1 t=k t=T-1 t=T

Pb/CW Pb/CW Pb/CW Pb/CW Pb/CW Pb/CW

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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . t=0 t=1 t=k-1 t=k t=T-1 t=T

Pb/CW Pb/CW Pb/CW Pb/CW Pb/CW Pb/CW

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Decrementing CW Safety V2V Minimum CW Razvan Stanica University of Toulouse ICC 2011 Congestion Control Enhancements of IEEE 802.11p Protocol for Access Control on a VANET Control Channel

Impact of the Minimum Contention Window

 Small CW – increased number of collisions  High CW – increased number of expired beacons  Beware: an expired beacon is lost for all the neighbours

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Decrementing CW Safety V2V Minimum CW Razvan Stanica University of Toulouse ICC 2011 Congestion Control Enhancements of IEEE 802.11p Protocol for Access Control on a VANET Control Channel

New Back-off Mechanism

 Can not detect collisions

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Decrementing CW Safety V2V Minimum CW Razvan Stanica University of Toulouse ICC 2011 Congestion Control Enhancements of IEEE 802.11p Protocol for Access Control on a VANET Control Channel

New Back-off Mechanism

 Can not detect collisions  We can detect expired beacons

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Decrementing CW Safety V2V Minimum CW Razvan Stanica University of Toulouse ICC 2011 Congestion Control Enhancements of IEEE 802.11p Protocol for Access Control on a VANET Control Channel

New Back-off Mechanism

 Can not detect collisions  We can detect expired beacons  Relatively high initial CW= 60  CW = CW/2 after every expired beacon  CW goes back to the initial value after N beacons

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Decrementing CW Safety V2V Minimum CW Razvan Stanica University of Toulouse ICC 2011 Congestion Control Enhancements of IEEE 802.11p Protocol for Access Control on a VANET Control Channel

Simulation scenario

 JiST/SWANS framework  Street Random Waypoint Mobility Model  Beaconing frequency 10 Hz (beacons can expire)  Different road topologies  Medium and high density

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Decrementing CW Safety V2V Minimum CW Razvan Stanica University of Toulouse ICC 2011 Congestion Control Enhancements of IEEE 802.11p Protocol for Access Control on a VANET Control Channel

current standard Beaconing reception probability at less than 200m from the source best fixed CW reverse backoff current standard best fixed CW reverse backoff 68% 77% 78% Medium density High density 56% 64% 64%

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Decrementing CW Safety V2V Minimum CW Razvan Stanica University of Toulouse ICC 2011 Congestion Control Enhancements of IEEE 802.11p Protocol for Access Control on a VANET Control Channel

current standard Beaconing reception probability at less than 200m from the source best fixed CW reverse backoff current standard best fixed CW reverse backoff 68% 77% 78% Medium density High density 56% 64% 64% Not the same

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Decrementing CW Safety V2V Minimum CW Razvan Stanica University of Toulouse ICC 2011 Congestion Control Enhancements of IEEE 802.11p Protocol for Access Control on a VANET Control Channel

Impact on the number of consecutive lost beacons

 alleviate the “ghost node” problem  can be used to give priority to DENs over CAMs

Reverse backoff Best fixed CW Less than 10 beacons Between 10 and 20 beacons More than 20 beacons

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Enhancements of IEEE 802.11p Protocol for Access Control on a VANET Control Channel Razvan Stanica University of Toulouse ICC 2011

Conclusion

 Contention window: very important in IEEE 802.11  IEEE 802.11p – many amendments at the physical layer  MAC layer (IEEE 802.11e) – good for multimedia applications in WLAN  VANET safety applications should be considered

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