Department of Information Engineering University of Padova{fasoloel, zanella, zorzi}@dei.unipd.it
An Effective Broadcast Scheme for Alert Message Propagationin Vehicular Ad Hoc Networks
E. Fasolo, A. Zanella and M. Zorzi
Speaker Stefano Tomasin
June, 14th 2006.
An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks
Main aims of this study
To develop and improve a broadcast protocol to deliver alert messages as soon as possible in a vehicular scenario [3]Maximize the reliabilityMinimize the delivery latency
To propose an analytical model in orderTo evaluate the protocol performanceTo optimize the protocol parameters
Compare the proposed solution with other broadcast protocols by means of simulations
An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks
Smart Broadcast Protocol (SBP)
Main Features Position-based scheme Using only position information Running on the top of an IEEE 802.11-like system Completely distributed Absence of control traffic
System Model Long and narrow rectangular area (street) Nodes placed according to a Poisson distribution Nodes known own position
An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks
SBP: Initial Assumptions
The current source coverage area is split into n sub areas
At each sub area is associated a time interval named contention windows according to
S1Sn …
Propagation direction
Not considered area
Positive advancement towards the propagation
direction
AIM: Support the maximum advancement
of the broadcast message towards the propagation direction
An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks
The source sends the an RTB (Request To Broadcast) message Each node that receives correctly the RTB message
Determine the sector it belongs to Schedules the retransmission of a CTB (Clear To Broadcast) message after a backoff time
b selected in the contention window according to a uniform probability distribution function
Listen to the channel
Source send the message to the node which has transmitted the CTB message
SBP: Relay Election
S1Sn …Not considered area
Propagation direction
b11
b12
bn2
bn1
bj1
NEXT RELAY
An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks
SBP: Collision Resolution
S1
Sn
…
Not considered area
Propagation direction
b11
b11
bn2
bn1
bj1
If a node receives correctly another RTB message adjusts its backoff time according to the position of the new source
If a collision occurs ( two or more nodes select the same backoff time and send at the same time a CTB message) the procedure continue.
NEXT RELAY
A COLLISION OCCURS
An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks
Theoretical Analysis: Initial Assumptions
qh = the number of nodes that pick the same backoff value h in W
qh = 0 IDLE (I) No node transmits
qh > 0 COLLISION (C) A collision occurs
qh = 1 BROADCAST (B) A node wins the
contention and transmits the broadcast message
nU = number of unsuccessful events before the completion of the procedure
TU = average duration of an unsuccessful countdown step
An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks
Theoretical Analysis: One-hop latency
The one-hop latency is defined as the mean time required before the broadcast message is successfully forwarded to the next relay node
where the last terms accounts for the extra time spent to restart the procedure is negligible
Finally, we have the simplify equation for the one-hop latency
where K = TC / TI
An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks
Theoretical Analysis: One-hop message progress
The one–hop message progress, δ, is defined as the additional distance covered by the message in a rebroadcast phase, on average
We only need to determine the statistic of J: We evaluate the conditioned
probability that s = h, given that s in W Ps(h)
And we use Ps(h) to evaluate Pj(r) and the the mean value of J
An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks
Theoretical Analysis: Optimization
Consider the following cost function defined as the time required to get the success retransmission over the successful probability
COST FUNCTION
Single solution in [1/K, 1]If we fix Ns
An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks
Validation of the theoretical analysis
One hop latency at varying of node density for different cw (assuming Ns = 10) Lines refer to the
theoretical results Marks refer to the
simulation outcomes
The interpolation of the minimum values correspond to the line obtained with cwopt
An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks
Analytical Model versus Simulations
Average one–hop progress δ and propagation speed v versus the node density λ (assuming cw = cwopt)
Good matching between analytical model and simulations High node densities assure the maximum progress
An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks
Protocol comparison
From the figure we can observe that the propagation speed achieved by SB is almost constant when varying the node density
SB may lead to a slightly lower advancement than the other schemes. This is due to the fact that SB balances both the message progress and the latency.
SB is compared with MCDS-based, GeRaF and UMB
An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks
Conclusions
We designed a protocol for message dissemination which guarantee high reliability and low latency
The developed analytical model assures good matching with the simulation results
SB outperforms the other message dissemination mechanisms.
Future work123
An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks
References
[1] D. Cottingham, “Research Directions on Inter-vehicle Communication,” http://www.cl.cam.ac.uk/users/dnc25/references.html, Dec. 2004.
[2] M. Rudack, M. Meincke, K. Jobmann, and M. Lott, “On traffic dynamical aspects intervehicle communication (IVC),” in 57th IEEE Semiannual Vehicular Technology Conference (VTC03 Spring), Jeju, South Korea, Apr. 2003, http://portal.acm.org/citation.cfm?id=778434.
[3] Fasolo, E. and Furiato, R. and Zanella, A., “Smart Broadcast for inter–vheicular communications,” in Proc. of WPMC05, Sep. 2005.
[4] Zanella, A. and Pierobon, G. and Merlin, S., “On the limiting performance of broadcast algorithms over unidimensional ad-hoc radio networks,” in Proceedings of WPMC04, Abano Terme, Padova, Sep. 2004.
[5] Korkmaz, G. and Ekici, E. and O¨ zgu¨ner, F. and O¨ zgu¨ner, U¨ ., “Urban multi-hop broadcast protocol for inter–vehicle communication systems,” in Proc. of the first ACM workshop on Vehicular ad hoc networks , 2004.
[6] M. Zorzi and R. Rao, “Geographic Random Forwarding (GeRaF) for ad hoc and sensor networks: energy and latency performance,” IEEE Transaction on Mobile Computing, vol. 2, no. 4, Oct.–Dec. 2003.
[7] B. Williams and T. Camp, “Comparison of broadcasting techniques for mobile ad hoc networks,” in MOBIHOC, 2002.
[8] K.M. Alzoubi and P.J. Wan and O. Frieder, “New distributed algorithm for connected dominating set in wireless ad hoc networks,” in Proc. Of 35th Hawaii Int’l Conf. on System Sciences (HICSS-35), Jan. 2002.
[9] P.J. Wan and K. Alzoubi and O. Frieder, “Distributed construction of connected dominating set in wireless ad hoc networks,” in Proc. of IEEE INFOCOM’2002, June 2002.
[10] S. Giordano and I. Stojmenovic, Position based routing algorithms for ad hoc networks: a taxonomy. Kluwer, 2004, pp. 103–136.
[11] I. Stojmenovic, “Position-based routing in ad hoc networks,” IEEE Communications Magazine, vol. 40, no. 7, pp. 128–134, July 2002.
Department of Information Engineering University of Padova{fasoloel, zanella, zorzi}@dei.unipd.it
An Effective Broadcast Scheme for Alert Message Propagationin Vehicular Ad Hoc Networks
E. Fasolo, A. Zanella and M. Zorzi
Speaker Stefano Tomasin
June, 14th 2006.
An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks
An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks
An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks
An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks
An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks
Inter-vehicular networks (IVNs)
Applications and services Emergency notification Cooperative driving assistance Car to car audio/video communications Internet access Traffic control
Topical features No energy constraints High mobility Availability of timing and localization information
Main Issues New paradigm (physical, MAC, routing layer solutions) New broadcast propagation mechanisms
• Efficient• Reliable• Low latency
An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks
The Broadcast Storm Problem
FloodingHigh Data Redundancy Collision Problem
MCDS-based algorithms Minimize the retransmitting node numberSolve the collision problemNot feasible in high dynamic networks
An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks
Broadcast Protocol Overview
Probabilistic Schemes Not solve collision and redundancy problem
Neighbor-based Schemes Require control traffic, depend on the network topology
Topology-based Schemes More efficient but require a complete topology knowledge (not
feasible for high dynamic networks) Cluster-based Schemes
High cost to maintain clustering structure in mobile networks Position-based Schemes
Flat, not require control traffic• Urban Multi-hop Protocol (UMBP)
An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks
The time wasted during the re-broadcast procedure depends on The collision probability
The probability that the furthest sub-areas are empty
Fixed Ns, for each node density, there is an optimum contention window size such thatThe time wasted on re-broadcast procedure is minimized
Some theoretical observations
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