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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