DEFINIZIONE E ANALISI DI STRATEGIE DI ALLOCAZIONE DINAMICA DEI CANALI IN P.R.I.M.O.

1
Special Interest Group on
NEtworking Telecommunications
An Effective Broadcast Scheme for Alert Message
Propagationin Vehicular Ad Hoc Networks
An Effective Broadcast Scheme for Alert Message
Propagationin Vehicular Ad Hoc Networks
E. Fasolo, A. Zanella and M. Zorzi
E. Fasolo, A. Zanella and M. Zorzi
A note on the use of these ppt slidesWere
making these slides freely available to all,
hoping they might be of use for researchers
and/or students. Theyre in PowerPoint form so
you can add, modify, and delete slides
(including this one) and slide content to suit
your needs. In return for use, we only ask the
followingIf you use these slides (e.g., in a
class, presentations, talks and so on) in
substantially unaltered form, that you mention
their source.If you post any slides in
substantially unaltered form on a www site, that
you note that they are adapted from (or perhaps
identical to) our slides, and put a link to the
authors webpage www.dei.unipd.it/zanella Thank
s and enjoy!
2
Special Interest Group on
NEtworking Telecommunications
www.dei.unipd.it/ricerca/signet
An Effective Broadcast Scheme for Alert Message
Propagationin Vehicular Ad Hoc Networks
E. Fasolo, A. Zanella and M. Zorzi
Department of Information Engineering University
of Padovafasoloel, zanella, zorzi_at_dei.unipd.it
Speaker Stefano Tomasin
June, 14th 2006.
3
Aim of the study

• Design a broadcast protocol for alert message
  delivery in a vehicular scenario
• Maximize reliability
• Minimize delivery latency
• Analytical modeling of the protocol
• Evaluate protocol performance
• Optimize protocol parameters
• Comparison with other broadcast protocols

4
Smart Broadcast Protocol (SBP)?

• Main Features
• Position-based scheme
• Running on top of IEEE 802.11-like system
• Completely distributed
• Limited control traffic
• System Model
• Street Long and narrow rectangular area
• Nodes placed according to a Poisson distribution
• Nodes known their own position only

5
SBP Initial Assumptions
Forbidden area
AIM Maximize broadcast-message advancement
along propagation line

• Coverage area is split into n sectors Si
• Sectors are assigned adjacent contention windows
  Wj, j1...,n

S1
Sn

Msg propagation direction
W1
Wn
W2
Wi
0
cwi
cw1 cw2... cwn
Positive advancement in the propagation direction
Propagation direction
6
SBP Relay Election

• Source sends an RTB (Request To Broadcast)
  message
• Nodes that receive RTB message
• Determine the sector they belong to
• Schedule the retransmission of a CTB (Clear To
  Broadcast) message after a random backoff time b
  uniformly selected in their contention window
• Countdown _at_ each idle slot, freeze in busy slots
• Node that first transmits successfully a CTB
  (Clear To Broadcast) message becomes the Next
  Relay

NEXT RELAY
Source
Contention Winner
Backing off node
7
SBP Collision Resolution
NEXT RELAY
Source

• If two or more nodes select the same backoff
  time, CTB messages will collide
• After collisions, procedure is resumed by the
  other backing off nodes (if any)?
• If any CTB message is received before the maximum
  backoff period has elapsed, procedure is started
  anew

Contention Winner
b11
bn2
Backing off node
Collided node
Sn
bj1
bn1

b11
S1
A COLLISION OCCURS
Propagation direction
8
Theoretical Analysis Initial Assumptions

• Nodes are distributed with density ? in each
  sector
• Nodes in sector Sj select backoff slots in Wj
  independently and uniformly
• Let qh be the number of nodes that select the
  same backoff slot h?Wi
• qh is a Poisson random variable with parameter

9
Theoretical Analysis Events probability

• Lets focus on events that may occur in slot h
• qh 0 ? IDLE (I) ? No nodes transmit
• qh gt 0 ? COLLISION (C)? A collision occurs
• qh 1 ? BROADCAST (B) ? A node wins the
• contention and gets the broadcast message to be
• forwarded
• nU average number of unsuccessful events before
  the completion of the procedure
• TU average duration of an unsuccessful
  countdown step

Collision duration
Idle slot duration
10
Theoretical Analysis One-hop latency

• Def One-hop latency ??
• mean time before broadcast message is
  successfully forwarded to the next relay node

K TC / TI
11
Theoretical Analysis One-hop message progress

• Onehop message progress, d average one-hop
  covered distance

Next Relay sector
Total number of sectors
Sector size (along the propagation direction)?
12
Theoretical Analysis Optimization

• Optimize the Cost Function
• One-hop delay/success probability

COST FUNCTION
Single solution in 1/K, 1
13
Validation of the theoretical analysis
Impact of CW setting on per-hop latency (Ns 10)?
Setting cwcwopt(?) ?? we interpolate the minima
of curves obtained with fixed cw
14
Analytical Model versus Simulations
Average onehop progress d
Average propagation speed v
??, cw cwopt(?)?

• Good matching between analytical model
  simulations
• High node densities assure maximum progress

15
Protocols comparison
SB vs MCDS-based, GeRaF and UMB

• SB propagation speed is almost constant when
  varying the node density
• SB may lead to slightly lower advancement than
  other schemes
• (SB balances both the message progress and the
  latency)?

16
Conclusions

• Smart Broadcast provides good performance in
  message dissemination along mono-dimensional
  networks of vehicles
• Analytical model permits in-depth analysis and
  optimization
• Future work
• Consider contention with other broadcast flows
• Include more realistic radio channel model

17
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.or
  g/citation.cfm?id778434.
• 3 Fasolo, E. and Furiato, R. and Zanella, A.,
  Smart Broadcast for intervheicular
  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 zguner, F.
  and O zguner, U ., Urban multi-hop broadcast
  protocol for intervehicle 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 Intl 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 INFOCOM2002, June 2002.
• 10 S. Giordano and I. Stojmenovic, Position
  based routing algorithms for ad hoc networks a
  taxonomy. Kluwer, 2004, pp. 103136.
• 11 I. Stojmenovic, Position-based routing in
  ad hoc networks, IEEE Communications Magazine,
  vol. 40, no. 7, pp. 128134, July 2002.

18
An Effective Broadcast Scheme for Alert Message
Propagationin Vehicular Ad Hoc Networks
E. Fasolo, A. Zanella and M. Zorzi
Department of Information Engineering University
of Padovafasoloel, zanella, zorzi_at_dei.unipd.it
Speaker Stefano Tomasin
June, 14th 2006.
19
Spare Slides
20
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

21
The Broadcast Storm Problem

• Flooding
• High Data Redundancy
• Collision Problem

• MCDS-based algorithms
• Minimize the retransmitting node number
• Solve the collision problem
• Not feasible in high dynamic networks

22
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)?

23
Some theoretical observations

• 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 that
• The time wasted on re-broadcast procedure is
  minimized

24
(No Transcript)
25
Theoretical Analysis One-hop message progress

• Onehop message progress, d average one-hop
  covered distance

• 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