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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

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
Outline
  • Introduction to Vehicular Network
  • Model of MAC in V2I communication
  • Simulation
  • Conclusion
why vehicular networks
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
v2v and v2i communications
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)

standard and research efforts
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

standard and research efforts cont d
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

problem statement
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
network model
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
markov model of vehicle nodes
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
simulation setup
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
nodal throughput in each zone n
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
increasing velocity
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
conclusion
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.
question and answers

Question and Answers ?

Thank you !

bbcr.uwaterloo.ca/~hluan

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