1. TDMA Slot Reservation in Cluster-Based VANET Ph.D. Gathering By Mohammad S. Almalag Advisor Michele C. Weigle Department of Computer Science Old Dominion University Norfolk, VA 1 11/17/2011

2. Introduction Vehicular Ad-Hoc Network (VANET): ▫Increase traveler safety ▫Decrease traveling time and fuel consumption ▫Increase on board luxury 11/17/2011 2

3. Introduction 11/17/2011 3 Applications categories: Safety  Co-operative Collision warning [V-V]  Intersection Collision Warning  Approaching Emergency Vehicle  Work Zone Warning [R-V] Non-safety  Traffic Information  Data Transfer  Parking Lot Payment  Electronic Toll Collection

4. Introduction Dedicated Short Range Communication (DSRC) channels: 11/17/2011 4

5. Introduction IEEE 1609.4 standard: 11/17/2011 5

6. Problem Safety messages requirements ▫High reliability ▫Every 100 msec [Wang, ACM VANET 2008] 11/17/2011 6 Non-Safety messages almost shut down Low Medium High Traffic Density

7. Objective The main objective: ▫Allow vehicles to efficiently exchange both safety and non-safety messages while meeting safety message requirements 11/17/2011 7

8. TDMA Time Division Multiple Access (TDMA) is a method used to enable multiple nodes to transmit on the same frequency channel. 04/27/2011 8

9. TDMA Assignment Assumptions:  Clusterhead based clustering scheme  One transceiver on-board  vehicles are equipped with GPS  1 CCH (cch)  6 SCHs (k)  N vehicles  τ is the slot size in SCHs  a mini-slot on the control channel to contain at least 64 bytes; (i.e. assuming k=6, this implies a slot size of 384 bytes) 11/17/2011 9

10. TDMA Assignment 11/17/2011 10

11. TDMA Assignment Each vehicle in the cluster will receive a local ID (from 1 to N). The CH will have always ID 1. ID 0 is reserved for a “virtual vehicle”. In each logical frame vehicle j, owns: ▫channel j mod k during time slot ; we also say that vehicle j owns the ordered pair ▫The j-th mini-slot of slot mod on channel cch 11/17/2011 11

12. TDMA Assignment Example: ▫Number of vehicles N = 61, k = 6, vehicle j’s ID= 39 11/17/2011 12 SCH: (39 mod 6) = 3 During slot And CCH: 4 th mini-slot in slot 6-1=5

13. TDMA Assignment ▫Notice that the Integer Division Theorem guarantees that if i ≠ j then either:  or  i mod k ≠ j mod k, or both 11/17/2011 13

14. Intra-cluster Communication Lightweight communication protocols Each vehicle uses its own mini-slot to disseminate safety beacons First byte, 2 8 = 128 different situations. 04/27/2011 14

15. Intra-cluster Communication Example:  0 : vehicle is not communicating at the moment.  1 : vehicle is involved in communicating with some other vehicle in the cluster. (Unicast)  2 : vehicle is involved in communicating with some other vehicle in the cluster. (multicast group)  125 : confirmation of “Hello” message.  126 : vehicle will transmit a request during its upcoming slot (i.e., next slot).  127 : vehicle will use its upcoming slot to transmit. 04/27/2011 15

16. Intra-cluster Communication Disseminating intra-cluster safety /governance messages: ▫Emergency messages:  Disseminated by CH.  127 for broadcast  N-bit vector for subset ▫Cluster control messages:  Disseminated by CH 04/27/2011 16

17. Intra-cluster Communication Disseminating intra-cluster non-safety messages: ▫Unicast:  Set up without CH intervention.  Using the local ID for channel and slot time. ▫Multicast:  Small group of vehicles:  Set up without CH intervention.  Big group of vehicles:  Set up with CH intervention. 11/17/2011 17

18. Inter-cluster Communication Vehicle-to- Infrastructure (V2I): 11/17/2011 18 17

19. Questions 11/17/2011 19

20. Cluster maintenance Cluster topology changes: ▫CH leaving the cluster. ▫A new vehicle joining the cluster. ▫A cluster member leaving the cluster. ▫Two single hop clusters get in range of each other. ▫A multi-hop cluster shrinks into a one-hop cluster. 04/27/2011 20

21. Cluster maintenance CH leaving the cluster: 04/27/2011 21

22. Cluster maintenance Two single hop clusters get in range of each other: 04/27/2011 22

23. Cluster maintenance A multi-hop cluster shrinks into a one-hop cluster: 04/27/2011 23