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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
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Introduction Vehicular Ad-Hoc Network (VANET): ▫Increase traveler safety ▫Decrease traveling time and fuel consumption ▫Increase on board luxury 11/17/2011 2
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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
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Introduction Dedicated Short Range Communication (DSRC) channels: 11/17/2011 4
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Introduction IEEE 1609.4 standard: 11/17/2011 5
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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
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Objective The main objective: ▫Allow vehicles to efficiently exchange both safety and non-safety messages while meeting safety message requirements 11/17/2011 7
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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
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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
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TDMA Assignment 11/17/2011 10
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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
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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
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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
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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
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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
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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
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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
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Inter-cluster Communication Vehicle-to- Infrastructure (V2I): 11/17/2011 18 17
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Questions 11/17/2011 19
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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
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Cluster maintenance CH leaving the cluster: 04/27/2011 21
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Cluster maintenance Two single hop clusters get in range of each other: 04/27/2011 22
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Cluster maintenance A multi-hop cluster shrinks into a one-hop cluster: 04/27/2011 23
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