A new Cooperative Strategy for Deafness Prevention in Directional Ad Hoc Networks

Andrea Munari, Francesco Rossetto, and Michele Zorzi

University of Padova, Italy

IEEE ICC 2007

Outline

Introduction Related Work Antenna Model Cooperative MAC (CMAC) Simulation Conclusions

Introduction

Wireless ad hoc networks are radio-based systems that do not need an access point or base station to operate.

When antenna arrays are employed. Directional transmissions enable a spatial reuse of the channel.

Introduction

Deafness A terminal is said to be deaf if it does not

answer an RTS message addressed to it.

A BRTS

Introduction

Deafness in directional RTS

A

D

E

B

C

F

I can’t hear anything.

Introduction

In Omni-directional RTS

A

D

E

B

C

F

I can’t send to B.

I can’t send to B.

I can’t send to B.

I can’t send to B,C.

I can’t send to B,C,D.

Related Work

Circular RTS/CTS Mechanism (CRCM) RTS and CTS packets are broadcast omni-direc

tionally by means of a sequence of directional transmissions.

A

B RTS

CTS

DATA

Motivation There is still some deafness problems in

directional transmissions.

A

D

E

B

C

F

I can’t hear anything.

I can’t send to A.

I can’t send to A.

I can’t send to A,B.

I can’t send to B,C.I don’t hear

anything.

Goal

CMAC proposes a cooperation scheme among nodes, trying to inform terminals that go back to idle mode after a transmission about communications that have started in the meantime.

Antenna Model

Each node can decode more than one packets simultaneously, provided that they come from different directions.

Each node can’t receive anything during the transmission.

Cooperative MAC (CMAC)

CMAC employs three solutions to let the nodes have a fair image of their neighbors’ state Circular delivery of RTS and CTS. Multiple Receptions. Cooperation among nodes.

Cooperative MAC

Cooperation among nodes The main cause of deafness is a mistaken idea o

f the network activity. This mechanism helps the nodes to know the ne

w links built during the transmission. Each node maintains an internal table, called C

ommunication Register (CR), where all the known ongoing communications are reported.

Cooperative MAC

A

D

E

B

C

F

Node id Time Left

A 5

Node id Time Left

A 4

B 10

Node id Time Left

B 10Node id Time Left

B 6

Node id Time Left

A 5

I should be update A’CR.

Node id Time Left

B 6Node id Time Left

A 4

Node id Time Left

B 6

Collaboration frame

Simulation

Simulator OPNET (version 11.5)

Parameters

Nodes 10 (in single hop)

Area 1500m x 1000m

Antennas 8 antennas

Data rate 1 Mbits/s

Traffic rate Poison traffic at nominal rates of 8,16,25,50,100,150 packets/s

Packet sizes

RTS 240 bits

CTS 240 bits

Collaboration 120 bits

Data 10240 bits

ACK 120 bits

CRCM MUD L-CMAC B-CMAC

Circular delivery of RTS/CTS O O O O

Multiple receptions O O O

Cooperation among nodes O O

The overhead of collaboration frames

O

Interference is generated by collaboration frames

O

The size of collaboration frames

120 bits (fixed)

Optimal

The low bound of CMAC

The upper bound of CMAC

MultiUser Detection

Simulation

Link failures vs. load (10 nodes)

Link Failures=

RTS theof All

RTSfault totalThe

Simulation

Power consumption vs. load (10 nodes)

Simulation

Throughput vs. effective load (10 nodes)

Throughput=

ratebit * timeSimulation

bitssent ly Successful

Load=

ratebit * timeSimulation

bitssent Totally

Conclusion

The cooperation in this paper is used for telling the nodes correct information.

The impact of our solutions on multihop networks and routing is an interesting problem and is part of our future work.

Thank you~