1. 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

2. Sections Broadcasting in wireless ad hoc networks.
Multipoint Relays (MPRs).
Our new algorithm.
Conclusion and future work.

3. Broadcasting in wireless ad hoc networks
Section 1
Section 2
Section 3
Section 4
Broadcasting in wireless ad hoc networks
It is commonly used in routing protocols.
As a necessary mechanism in various applications that need to maintain global network information (paging a particular host or sending alarm signals).

4. Network wide broadcast in ad hoc networks
Section 1
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Section 4
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

5. Proposed broadcast algorithms
Section 1
Section 2
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Section 4
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.

6. Neighbor–designating algorithms
Section 1
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Section 4
Neighbor–designating algorithms
Each node informs neighbor nodes about its node information such as node IDs of neighbor nodes.
A node determines whether its neighbors should forward broadcast packets.

7. Neighbor–designating example
Section 1
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Section 4
Neighbor–designating example
Node S chooses its neighbors A, B and C to relay broadcast packets. B S A C

8. Cluster based algorithms
Section 1
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Section 4
Cluster based algorithms
Network is clustered and cluster-heads are elected. Cluster-heads are referred to as dominators.
Cluster-heads select some connectors to connect other cluster-heads.

9. Cluster example Dominators: {A, B, C} Connectors: {1, 2} Section 1

10. Multipoint Relays (MPRs)
Section 1
Section 2
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Section 4
Multipoint Relays (MPRs)
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.

11. Multipoint Relays example
Section 1
Section 2
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Section 4
Multipoint Relays example
a {1, 2, 3}
b {3, 4, 5}
e {6, 7, 8}
f {8}
c { }
d { } 2
e {6, 7, 8}
b {4, 5}
f {8}
c { }
d { }
b {4, 5}
f { }
c { }
d { } 3 1 4 a
Selected MPRs: {a, b, e} b 5 f c 8 e d 7 6

12. Our Gateway Multipoint Relays (GMPR)
Section 1
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Section 4
Our Gateway Multipoint Relays (GMPR)
It is a combination of Clustering and Multipoint Relay methods.
Each node in the network can be in one of the four states: dominator, dominatee, connector and candidate.
Dominator: It is the cluster-head, and it performs MPR calculation.
Dominatee: The nodes connected by dominators.
Node states
Connector: Can only be entered from dominatee state.
Candidate: Initial state that attends dominator election.

13. Section 1
Section 2
Section 3
Section 4
Operations of GMPR
Dominators (nodes that covers most number of candidates) are elected in the network where all nodes can be covered by the dominators.
Each dominator selects MPRs to cover its two-hop neighbor nodes.
An MPR is a connector if it is selected by the largest dominator of this MPR.
Only dominators and connectors forward broadcast packets.

14. Gateway Multipoint Relays example
Section 1
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Gateway Multipoint Relays example
Elect dominators based on the candidate coverage.
Dominators calculate MPRs to cover two-hop neighbor nodes.
Each MPR decides whether it is the connector.
Selected by “H”
Selected by “H” I E A J H F
Selected by “P” T B D K
Selected by “D” C L P G O M
Selected by “P” N
Selected by “D”

15. Self-pruning procedure
Section 1
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Self-pruning procedure
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.

16. Self-pruning procedure example
Section 1
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Self-pruning procedure example
After selecting connectors
Dominators: E, H
Connector: F A G B E F H
Then Both dominators apply self-pruning procedure, and H becomes a silent-dominator. C I D

17. 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.

18. Transmission range R = 25m
Section 1
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Simulation results
Transmission range R = 25m

19. Transmission range R = 50m
Section 1
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Simulation results
Transmission range R = 50m

20. Conclusion and future work
Section 1
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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.

21. References
[1]. J. Wu and F. Dai, “A generic distributed broadcast scheme in ad hoc wireless networks,” in Proceedings of MOBIHOC, 2002, pp
[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 [online]. Available:

22. Questions?

23. Thank you!

24. Probability based algorithms
Section 1
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Section 4
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.

25. Distance based algorithms
Section 1
Section 2
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Section 4
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.
Problems:
Energy wastage (unnecessary broadcast)
Cannot guarantee full coverage d1 d2 S A B

26. Location based algorithms
Section 1
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Section 4
Location based algorithms
Use positioning devices such as GPS (Global Positioning System) to provide precise locations of hosts in a network.
Additional coverage
A host retransmits a broadcast packet if the additional area it covers is larger than a threshold value. d1 d2 S A B