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

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

Introduction 11/17/ 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

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

Introduction IEEE standard: 11/17/2011 5

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

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

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

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

TDMA Assignment 11/17/

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/

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

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/

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/

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/

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/

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/

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

Questions 11/17/

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/

Cluster maintenance CH leaving the cluster: 04/27/

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

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