Name : Dinesh Bilimoria Date: Oct 23rd, 2013
Post on 24-Feb-2016
36 Views
Preview:
DESCRIPTION
Transcript
CSLI 5350G - Pervasive and Mobile ComputingWeek 6 - Paper Presentation“Exploiting Beacons for Scalable Broadcast Data Dissemination in VANETs”
Name: Dinesh BilimoriaDate: Oct 23rd, 2013
2
Research Paper
Bibliography:
Schwartz, R. S., Das, K., and Scholten, H. and Havinga, P.(2012) Exploiting beacons for scalable broadcast data dissemination in VANETs. In: 9th ACM International Workshop on Vehicular Inter-Networking, Systems, and Applications, VANET 2012.
3
Exploiting beacons for scalable broadcast data dissemination in VANETs
Broadcast Suppression Simple flooding, probability based, area based, neighbor knowledge
methods do not take into account the highly dynamic environment present on roads and predictable mobility pattern of vehicles’ movements.
In Broadcast Storm Problem, flooding scheme results in excessive redundancy, contention, and collision rates.
Broadcasting with CSMA/CA in the 802.11p is unreliable due to the lack of acknowledgments.
1-hop or 2-hop neighborhood information become outdated due to high speed of vehicles.
Adding neighborhood information to periodic messages results in high network overhead.
Current delay-based schemes still suffer from high levels of contention and collision when the number of vehicles rebroadcasting nearly simultaneously is high in dense networks.
4
Exploiting beacons for scalable broadcast data dissemination in VANETs
Broadcast Suppression Techniques Common approach to reduce broadcast redundancy and end-to-end delay in
VANETs is to give highest priority to the most distant vehicles towards the message direction.
Three ways of assigning this priority; Weighted p-Persistence;
- the farthest vehicles rebroadcast with highest probability
Slotted 1-Persistence; - vehicles with highest priority are given the shortest delay
before rebroadcasting
Slotted p-Persistence; - vehicles with highest priority the shortest delay and highest probability to rebroadcast
5
Exploiting beacons for scalable broadcast data dissemination in VANETs
Broadcast Suppression Techniques
6
Exploiting beacons for scalable broadcast data dissemination in VANETs
Issues and Challenges With delay-based schemes, scalability issues are seen as there is inability to
dynamically choose the optimal value for the number and boundaries of the time slots used.
Time slots matched to geographical regions within the transmission range of the sender but this can lead to an uneven distribution of vehicles in each time slot.
est. total time taken
7
Exploiting beacons for scalable broadcast data dissemination in VANETs
Issues and Challenges In EMDV, the sender determines the next relay vehicle based on
neighborhood information received from beacons. In centralized approach selecting the next relay vehicle, problem arises
when vehicles transmit messages with different power levels. Sub-optimal vehicle selection, leading to higher end-to-end delays
8
Exploiting beacons for scalable broadcast data dissemination in VANETs
Objective Distributed Optimized Time (DOT) protocol aims at always selecting the
farthest vehicles, i.e., optimal relay vehicles, while controlling transmission redundancy used to increase robustness.
Proposal DOT has the following characteristics;
(1) Time slot density control: - positioning information of 1-hop neighbors to control with precision the time slots’ boundaries- prevents the uneven distribution of vehicles among time slots(2) Distributed:- each vehicle takes the decision regarding when to retransmit a message in a distributed fashion- prevents sub-optimal selections of a relay vehicle
9
Exploiting beacons for scalable broadcast data dissemination in VANETs
Contributions Propose the DOT protocol to tackle broadcast suppression.
Assumptions DOT runs on top of the MAC layer, thereby requiring no modification to IEEE 802.11p Relies on the existence of periodic beacons transmitted by each vehicle at a certain
rate Beacons are defined to be transmitted in the form of WAVE Short Messages (WSMs),
according to the IEEE 1609 WAVE The IEEE WAVE standard determines that these messages carry information such as
the data rate, channel number and the transmission power level employed Contextual information ie vehicle’s geographical position, speed and acceleration to
be included Each vehicle is equipped with a device capable of obtaining the current vehicle’s
geographical position, such as a GPS receiver Consider the following message header structure: <Vehicle ID, Message ID, Time
Stamp, Vehicle’s Geographical Coordinates, Power Level>
Exploiting beacons for scalable broadcast data dissemination in VANETs
Distributed Optimized Time (DOT) Each vehicle keeps a table of one-hop neighbors Tn. Each entry in Tn contains: <Vehicle ID, Expiration Time, Vehicle’s
Geographical Coordinates>. Time tolerance before removing an entry defined as tt = 2.5( 1 / bf), where bf
is the beaconing rate, e.g., 10 Hz. Every vehicle schedules a rebroadcast for message m with a time delay TSij. If any vehicle receives an echo of message m before TSij expires, it cancels
its rebroadcast and ignores future duplicates of m. TSij tasks (i) estimate which vehicles are within the transmission range of the
sender and received m (ii) Sort the entries of every vehicle in table Tn based on its geographical position.
11
Exploiting beacons for scalable broadcast data dissemination in VANETs
Distributed Sorting Algorithmsorts vehicles as
The time for vehicles to wait before rebroadcasting is given by:
# of vehicles in time slot
position of vehicles in
est. total time taken
additional delay
Exploiting beacons for scalable broadcast data dissemination in VANETs
How does DOT work ? - All vehicles in the sender’s range assigned individual time slots Rebroadcasts are separated in time by multiples of slot time st.
- Prevent nearly simultaneous rebroadcasts among the two vehicles in each time slot, higher waits for additional delay
OPTIMALRESULTS
13
Exploiting beacons for scalable broadcast data dissemination in VANETs
Estimating vehicles in the Sender’s Range DOT depends on accurately estimating which vehicles are within the
transmission range Equation for Transmission Range
14
Exploiting beacons for scalable broadcast data dissemination in VANETs
Simulation Parameters
15
Exploiting beacons for scalable broadcast data dissemination in VANETs
Results Results of performance of protocols with respect to delivery ratio
DOT and Optimized Slotted 1-persistence achieve near 100% in every transmission range settings
DOT presents lowest delay since fewer hops
DOT controls the time slot density regardless of the current density of the vehicles
16
Exploiting beacons for scalable broadcast data dissemination in VANETs
Results Analysis of the performance and when varying the main parameters.
17
Exploiting beacons for scalable broadcast data dissemination in VANETs
Open problems Although this paper focused in suppressing broadcast using 1-hop neighbor
information, what happens when using 2-hop neighbor is used. Incorporate DOT broadcast suppression using store-carry-forward scheme. Analytical method is required instead of using estimating vehicles in the
sender’s range. Priority to be embedded in message header
18
Exploiting beacons for scalable broadcast data dissemination in VANETsDiscussion points1. What is the difference between simple flooding and probability based flooding ? Simple flooding – no form of suppression
Probability flooding – rely on network topology to assign a probability to each broadcast
2. What is the difference between Weighted p-Persistence and Slotted 1-Persistence? Weighted p-Persistence;
- the farthest vehicles rebroadcast with highest probability Slotted 1-Persistence;
- vehicles with highest priority are given the shortest delay before rebroadcasting
3. Using the DOT sorting algorithm,what is vehicle v1’s sorting list? <v3,v2,v1,v0>
v0
v1
v2 v3
top related