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. 2 Outline 1.Introduction to Vehicular Network 2.Model of MAC in V2I communication 3.Simulation 4.Conclusion 2

3. 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 3

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

5. 5 Standard and Research Efforts 5 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 [1] J. Ott and D. Kutscher, "Drive-thru Internet: IEEE 802.11 b for 'automobile' users," in IEEE INFOCOM, 2004 Image from http://www.drive-thru-internet.org/

6. 6 CarTel in MIT [2] City-wide experiment showing the intermittent and short-lived connectivity, yet high throughput while available 6 [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 Small scale network without considering MAC Link layer and transport layer performance What if a great number of vehicles moving fast? Standard and Research Efforts (cont’d)

7. 7 Problem Statement MAC performance evaluation for fast-moving large 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 7

8. 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 p z for different zone n in Z 8 Mobility Model Sojourn time of vehicles in each zone n is geometrically distributed with mean t n Within a period, vehicle moves from zone n to n+1 with the probability /t n, and no change with the left probability

9. 9 Markov Model of Vehicle Nodes 9 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 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

10. 10 Simulation Setup 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 10 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

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

12. 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 12

13. 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. 13

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