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Gateway Multipoint Relays — an MPR-based Broadcast Algorithm For Ad Hoc Networks
Ou Liang, Ahmet Sekercioglu and Nallasamy Mani
Department of Electrical and Computer Systems Engineering
Monash University, Australia
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Sections
1. Broadcasting in wireless ad hoc networks.
2. Multipoint Relays (MPRs).
3. Our new algorithm.
4. Conclusion and future work.
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Broadcasting in wireless ad hoc networks
Section 1 Section 2 Section 3 Section 4
1. It is commonly used in routing protocols.
2. As a necessary mechanism in various applications
that need to maintain global network information
(paging a particular host or sending alarm signals).
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Network wide broadcast in ad hoc networks
Due to the limitation of radio power, a mobile node may not be
within the transmission range of all other nodes. Therefore,
broadcast packets have to be relayed by other recipient nodes.
S
Section 1 Section 2 Section 3 Section 4
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Proposed broadcast algorithms
Generally, broadcast algorithms in ad hoc networks
can be categorized into five groups [1]:
• Probability based algorithms.
• Distance based algorithms.
• Location based algorithms.
• Neighbor-designating algorithms.
• Cluster based algorithms.
Section 1 Section 2 Section 3 Section 4
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Neighbor–designating algorithms
1. Each node informs neighbor nodes about its node
information such as node IDs of neighbor nodes.
Section 1 Section 2 Section 3 Section 4
2. A node determines whether its neighbors should
forward broadcast packets.
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Neighbor–designating example
SA
C
B
Node S chooses its
neighbors A, B and
C to relay broadcast
packets.
Section 1 Section 2 Section 3 Section 4
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Cluster based algorithms
1. Network is clustered and cluster-heads are
elected. Cluster-heads are referred to as
dominators.
2. Cluster-heads select some connectors to connect
other cluster-heads.
Section 1 Section 2 Section 3 Section 4
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Cluster example
1A B
2
C
Dominators: {A, B, C}
Connectors: {1, 2}
Section 1 Section 2 Section 3 Section 4
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Multipoint Relays (MPRs)
Section 1 Section 2 Section 3 Section 4
It is a broadcast mechanism used in the Optimized Link
State Routing protocol (OLSR) [2, 3] , and it belongs to
the family of neighbor–designating algorithms.
Each node selects a subset of nodes from its one-hop
neighbors to cover all its two-hop neighbors.
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Multipoint Relays example
Section 1 Section 2 Section 3 Section 4
d
bf
a
ce
6
2
3
7
5
4
8
1
a {1, 2, 3}
b {3, 4, 5}
e {6, 7, 8}
f {8}
c { }
d { }
e {6, 7, 8}
b {4, 5}
f {8}
c { }
d { }
b {4, 5}
f { }
c { }
d { }
Selected MPRs: {a, b, e}
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Our Gateway Multipoint Relays (GMPR)
Section 1 Section 2 Section 3 Section 4
Node states
Dominator: It is the cluster-head, and it performs MPR calculation.
Dominatee: The nodes connected by dominators.
Connector: Can only be entered from dominatee state.
Candidate: Initial state that attends dominator election.
1. It is a combination of Clustering and Multipoint Relay
methods.
2. Each node in the network can be in one of the four states:
dominator, dominatee, connector and candidate.
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Operations of GMPR
Section 1 Section 2 Section 3 Section 4
1. Dominators (nodes that covers most number of candidates) are
elected in the network where all nodes can be covered by the
dominators.
2. Each dominator selects MPRs to cover its two-hop neighbor
nodes.
3. An MPR is a connector if it is selected by the largest
dominator of this MPR.
Only dominators and connectors forward broadcast packets.
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Gateway Multipoint Relays example
Section 1 Section 2 Section 3 Section 4
DB
F
AE
CG
H
I
J
OP
N
L
K
M
1. Elect dominators based on the candidate coverage.
2. Dominators calculate MPRs to cover two-hop neighbor nodes.
3. Each MPR decides whether it is the connector.
Selected by “H”
Selected by “D”
Selected by “H”
Selected by “P”
Selected by “P”
Selected by “D”
T
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Self-pruning procedure
Section 1 Section 2 Section 3 Section 4
Aim:
To further reduce retransmissions by preventing leaf-dominators
forwarding broadcast packets.
A dominator D is a leaf-dominator if it has a one-hop connector
that can cover all D’s one-hop neighbors.
A leaf-dominator is referred to as the Silent-dominator, which still
selects MPRs but does not retransmit broadcast packets.
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Self-pruning procedure example
Section 1 Section 2 Section 3 Section 4
GA
D
E HF
I
B
C
After selecting connectors
Dominators: E, H
Connector: F
Then Both dominators
apply self-pruning
procedure, and H becomes
a silent-dominator.
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Simulation studies
Section 1 Section 2 Section 3 Section 4
Simulator OMNeT++ with Mobility Framework.
MAC protocol Assume a perfect MAC layer (error and collision free).
Network area 100m x 100m two dimensional area.
Topology generating
Randomly distribute nodes in the area. Each node is placed within the transmission range of a previously placed node to make sure connectivity.
Number of nodes
Range from 20 to 100.
Transmission range
Two transmission ranges: 25m and 50m.
Number of runs A sufficient number of runs are conducted to achieve 95% confidence interval within a ±5% margin.
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Simulation results
Section 1 Section 2 Section 3 Section 4
Transmission range R = 25m
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Simulation results
Section 1 Section 2 Section 3 Section 4
Transmission range R = 50m
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Conclusion and future work
We have proposed a new efficient broadcast algorithm based on
the Multipoint Relays and clustering methods. Simulation studies
show that compared with related work, our algorithm generates
fewer forwarding nodes thus reducing retransmissions and
collisions.
Future work: investigate the performance of our algorithm in
both dense and mobile environment.
Section 1 Section 2 Section 3 Section 4
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References
[1]. J. Wu and F. Dai, “A generic distributed broadcast scheme in ad hoc
wireless networks,” in Proceedings of MOBIHOC, 2002, pp. 194-205.
[2]. A. Laouiti, A. Qayyum, and L. Viennot, “Multipoint relaying: an efficient
technique for flooding in mobile wireless networks,” in 35th Annual Hawaii
International Conference on System Sciences HICSS’2001.
[3].T. Clausen and P. Jacquet, “Optimized link state routing protocol (OLSR),”
RFC 3626, Oct. 2003. [online]. Available: http://www.faqs.org/rfcs/rfc3626.html.
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Questions?
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Thank you!
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Probability based algorithms
It is similar to the “blind flooding”, but each node
rebroadcast a packet with a predetermined probability
value “P”.
Problems:
• Can not guarantee full coverage in the network.
• Has little effect on in sparse network.
Section 1 Section 2 Section 3 Section 4
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Distance based algorithms
A node retransmit a broadcast packet if the distance between it
and the sender of the packet is larger than a predefined
threshold distance.
SA B
d1 d2
Problems:
• Energy wastage (unnecessary
broadcast)
• Cannot guarantee full
coverage
Section 1 Section 2 Section 3 Section 4
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Location based algorithms
Use positioning devices such as GPS (Global Positioning System)
to provide precise locations of hosts in a network.
SA B
d1 d2
Additional coverage
A host retransmits a
broadcast packet if the
additional area it covers
is larger than a threshold
value.
Section 1 Section 2 Section 3 Section 4