Name : Dinesh Bilimoria Date: Oct 23rd, 2013

1. CSLI5350G - 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 roadsand 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 • 1-hop or 2-hop neighborhoodinformation become outdated due to high speed of vehicles.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 BroadcastSuppression 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>

10. 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 mbefore TSijexpires, it cancels its rebroadcast and ignores future duplicates of m. • TSijtasks (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 Algorithm sorts vehicles as The time for vehicles to wait before rebroadcasting is given by: est. total time taken # of vehicles in time slot position of vehicles in additional delay

12. 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 OPTIMAL RESULTS

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 VANETs Discussion points 1. What is the difference between simple flooding and probability based flooding ? • Simple flooding – no form of suppressionProbability 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> v1 v2 v3 v0