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MAC Performance Analysis for Vehicle to Infrastructure Communication

MAC Performance Analysis for Vehicle to Infrastructure Communication. Tom H. Luan*, Xinhua Ling , Xuemin (Sherman) Shen* *BroadBand Communication Research Group University of Waterloo. §. Research In Motion. §. Outline. Introduction to Vehicular Network Model of MAC in V2I communication

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MAC Performance Analysis for Vehicle to Infrastructure Communication

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  1. MAC Performance Analysis for Vehicle to Infrastructure Communication Tom H. Luan*, Xinhua Ling , Xuemin (Sherman) Shen* *BroadBand Communication Research Group University of Waterloo § Research In Motion §

  2. Outline • Introduction to Vehicular Network • Model of MAC in V2I communication • Simulation • Conclusion

  3. Why Vehicular Networks ? • Internet becomes an essential part of our daily life • Watch video on Youtube; order literature on Amzone; catch the final moments of an eBay auction … • Americans spend up to 540 hours on average a year in their vehicles (10% of the waking time) • Internet access from vehicles is still luxury • Vehicular Network • To provide cheap yet high throughput data service for vehicles on the road

  4. V2V and V2I Communications Vehicle to RSU (V2R or V2I) • Infotainment: Internet access, video streaming, music download, etc. • MAC throughput performance evaluation of V2I communication Vehicle to Vehicle (V2V) RSU (roadside unit)

  5. Standard and Research Efforts • IEEE drafts 802.11p standard to permit vehicular communication • 802.11a radio technology + 802.11e EDCA MAC • Multi-channel: 6 service channels + 1 control channel • Drive-thru Internet • Using off-the-shelf 802.11b hardware, a vehicle could maintain a connection to a roadside AP for 500m and transfer 9MB of data at 80km/h using either TCP or UDP Image from http://www.drive-thru-internet.org/ [1] J. Ott and D. Kutscher, "Drive-thru Internet: IEEE 802.11 b for 'automobile' users," in IEEE INFOCOM, 2004

  6. Standard and Research Efforts (cont’d) • CarTel in MIT [2] • City-wide experiment showing the intermittent and short-lived connectivity, yet high throughput while available • Small scale network without considering MAC • Link layer and transport layer performance • What if a great number of vehicles moving fast? [2] V. Bychkovsky, B. Hull, A. Miu, H. Balakrishnan and S. Madden, "A measurement study of vehicular internet access using in situ Wi-Fi networks," in ACM MobiCom, 2006

  7. Problem Statement • MAC performance evaluation for fast-movinglarge scale vehicular networks • We consider 802.11b DCF • Used by most trail networks, e.g., Drive-thru • Compatible to WiFi device (e.g., iPod Touch) • The basis of 802.11p MAC

  8. Network Model • Perfect channel without packet loss and errors • Saturated case: nodes always have a packet to transmit • Multi-rate transmission according to the distance to RSU • Spatial zones: the radio coverage of one RSU is divide into Z = {0, 1, …, N} zones according to node transmission rate • p-persistent MAC: nodes transmit with a constant probability pz for different zone n in Z • Mobility Model • Sojourn time of vehicles in each zone n is geometrically distributed with mean tn • Within a period , vehicle moves from zone n to n+1 with the probability /tn, and no change with the left probability

  9. Markov Model of Vehicle Nodes • 2D Markov chain embedded at the commencement of the backoff counter countdown • Upon the decrement of backoff counter, vehicle may either move to the next zone or stay in the original zone • When coming into a new zone, different transmission probability is applied • Each node can be represented by {z(t), b(t)} • z(t): zone the vehicle is current in at time t • b(t): the value of backoff counter of the node at time t

  10. Simulation Setup • Radio coverage of RSU is 250m, which is divided into 8 zones • By default, 50 vehicles move at constant speed with v = 80 km/h • When arriving at the end of the road session (zone N), vehicles reenter zone 0 and start a new iteration of communication • Two schemes • Equal contention window (transmission probability p) in all zones • Differential contention window in zones

  11. Nodal Throughput in Each Zone n sn = Nodal Throughput in Each Zone Average pkt length in each trans. Mean interval between consecutive trans. Integrated Throughput Xnsn S = ∑ n Where Xn is the node population in zone n • Using equal CW in all zones would suffer from performance anomaly

  12. Increasing Velocity • With enhanced node velocity, nodes in front zones have higher throughput than the back zones • The small CW in zone 4 benefits the following zones • System throughput reduces when velocity increases

  13. Conclusion • Throughput performance evaluation of DCF in the vehicle to infrastructure communication • Increase the velocity would reduce the system throughput • Future work • Optimal design of DCF (contention window) • QoS provision with call admission control etc.

  14. Question and Answers ? Thank you ! bbcr.uwaterloo.ca/~hluan

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