IEEE Globecom 2010 Tan Le Yong Liu Department of Electrical and Computer Engineering Polytechnic Institute of NYU Opportunistic Overlay Multicast in Wireless.

IEEE Globecom 2010

Tan Le Yong LiuDepartment of Electrical and Computer Engineering

Polytechnic Institute of NYU

Opportunistic Overlay MulticastOpportunistic Overlay Multicastin Wireless Networkin Wireless Network

Outline

Introduction Motivation Goal

Network Model and Assumptions Definition

Minimum Steiner Tree Opportunistic Routing Simulation Conclusion

Introduction

Deliver multicast services efficiently over multi-hop wireless networks: Increasing popularity of wireless devices New wireless applications

It is well-known that the general minimum-cost multicast routing problem is NP-hard. Interferences Collisions Volatile link

Introduction

Opportunistic Routing (OR) has been proposed to improve the efficiency of unicast in multi-hop wireless networks.

The advantage of OR: Reduce the number of transmissions necessary to deliver a packet. Combine multiple weak links into one strong link.

S

A

B D

C

Traditional Routing: S→ B→D 4 + 4 = 8

Opportunistic Routing: S →ABC 1/(1-0.75^3)=1.73 A|B|C→D 4 S→ABC→D1.73+4=5.73

25% 25%

25%

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Introduction

Overlay networks have been widely employed to deliver multicast services on the Internet. A virtual network that is built on top of an existing network Implement a service that is not available in the existing network.

Introduction

For wireless multicast, we build an overlay Steiner tree to connect the source with all receivers.

Src

Recv 1

Recv 2

Introduction Goal

Build the Minimum Steiner Tree with Opportunistic Routing (MSTOR). Minimize the total transmission cost to reach all receivers

Network Model and Assumptions

We consider a network of N static wireless nodes, including One source node S A set of K receivers R={R1, R2, …, Rk}, where K<N

N-K-1 relay nodes

Wireless links between neighbor nodes are not reliable.

The success probability of packet transmission on a link is depends on Distance Density Traffic MAC scheduling scheme

Network Model and Assumptions

The length of a OR path from node i to node j is the expected number of packet transmissions to send a packet from i to j along the OR path.

i j k25% 10%

4

10

14

Minimum Steiner Tree Algorithm

S A B

R C D

1 1

11

3 26

S

R

Total length = 6

S A B

R C D1

36

S

R

Total length = 5

A B

C

1 1

1

2

Minimum Steiner Tree Algorithm

Approximate algorithm: Shortest Path algorithm Start with a subtree T consisting of one terminal node While T does not span all terminals

• Select a terminal x not in T that is closest to a vertex in T.

• Add to T the shortest path that connects x with T.

Delete non-terminals of degree 1 from this spanning tree Until there are no such non-terminals

S A B

R C D

36

S

R

A B

C

1 1

1

2

D1

Simulation

Compare the performance of MSTOR with The shortest path unicast routing (UR)

• The source sends packets to each receiver one by one

Unicast opportunistic routing (OR)• The source sends packets to each receiver one by one by following the

optimal unicast OR path.

Tree-based unicast routing (tree-based UR).• packets are sent to receivers along the minimum Steiner tree with the

unicast distance as link weight

The sending rate at physical layer is set to be 250Kb/s.

We configure the transmission power with the effective radio coverage of 200m.

Simulation

Topology The source is node 1, with two receivers node 7 and 10. The grid size is 70m. The average packet loss rate on each wireless link is around 10%

Simulation

Number of packets delivered MSTOR outperforms other routing schemes

Simulation

Number of packets delivered This demonstrates that MSTOR can improve the multicast efficiency

in wireless networks with high link loss rate.

Simulation

Topology 30 static nodes randomly located in an area of 1000m×1000m. We randomly choose one source and five receivers

Simulation

Number of packets delivered The big improvement of MSTOR is originated from the

• gains OR distance

• higher packet loss rates

• higher wireless node density

Simulation

Packet latency The time lag from the source sends out the first copy of a packet until

all receivers receive the packet successfully. This is because of the advantages of dynamic routes of OR over the

static routes of UR in a lossy wireless network.

Conclusion

In this paper, we studied opportunistic overlay multicast for wireless networks.

MSTOR simple protocol can be easily deployed in multi-hop wireless networks achieve high multicast efficiency