tdma slot reservation in cluster-based vanet ph.d. gathering by mohammad s. almalag advisor michele...
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TDMA Slot Reservation in Cluster-Based VANETPh.D. Gathering
ByMohammad S. AlmalagAdvisorMichele C. WeigleDepartment of Computer ScienceOld Dominion UniversityNorfolk, VA
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Introduction
Vehicular Ad-Hoc Network (VANET):▫Increase traveler safety▫Decrease traveling time and fuel
consumption▫Increase on board luxury
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Introduction
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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
IntroductionDedicated Short Range Communication (DSRC)
channels:
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IntroductionIEEE 1609.4 standard:
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Problem• Safety messages requirements
▫ High reliability▫ Every 100 msec
[Wang, ACM VANET 2008]
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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
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TDMATime Division Multiple Access (TDMA) is a method used to
enable multiple nodes to transmit on the same frequency channel.
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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)
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TDMA Assignment
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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
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TDMA Assignment
•Example: ▫ Number of vehicles N = 61, k = 6, vehicle j’s ID= 39
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SCH: (39 mod 6) = 3 During slot AndCCH: 4th 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
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Intra-cluster Communication• Lightweight communication protocols• Each vehicle uses its own mini-slot to
disseminate safety beacons • First byte, 28 = 128 different situations.
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Intra-cluster CommunicationExample:
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.
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Intra-cluster CommunicationDisseminating intra-cluster safety /governancemessages:
▫ Emergency messages: Disseminated by CH.
127 for broadcast N-bit vector for subset
▫ Cluster control messages: Disseminated by CH
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Intra-cluster CommunicationDisseminating 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.
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Inter-cluster CommunicationVehicle-to- Infrastructure (V2I):
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Questions
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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.
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Cluster maintenance
CH leaving the cluster:
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Cluster maintenance
Two single hop clusters get in range of each other:
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Cluster maintenance
A multi-hop cluster shrinks into a one-hop cluster:
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