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A Busy-Tone based MAC Scheme for Wireless Ad Hoc Networks using Directional

Antennas

Hong-Ning Dai, CUHKKam-Wing Ng, CUHK

Min-You Wu, SJTU

GLOBECOM 2007

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Outline

Introduction Related work Busy-Tone based Directional MAC

(BT-DMAC) Simulation results Conclusion

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Introduction

Benefit of directional antennas Transmission range Reduced interference Increased spatial reuse

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Drawback of directional antennas The hidden terminal problem The deafness problem

Introduction

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Hidden Terminal due to unheard RTS/CTS

D

CB

Data

ACTSDataRTSRTS

Collision!!

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Introduction (Deafness)

B

C

A

Data RTS

C does not know node A is busy. C keeps transmitting RTSs to node A

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Related Work Existing MAC protocols using direction

al antennas Directional MAC (DMAC) Dual Busy Tone Multiple Access with Dire

ctional Antennas (DBTMA/DA) Circular-DMAC Tone-based directional MAC (ToneDMAC)

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Motivation and Goal

Motivation There is no protocol that can completely

solve both the hidden terminals and deafness problems with low overhead

Goal Propose a new MAC protocol to attack th

e hidden terminal problem and the deafness problem

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Antenna Model

Each node equipped with two interfaces: Directional antenna(Switched beam)

two modes: omni-directional, directional Data transmission

Omni-directional antenna only used to send busy tones notification

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Busy Tone

Two omnidirectional busy tones: BTt (the transmitting busy tone) BTr (the receiving busy tone)

BTt and BTr is encoded with a beam No. and node ID

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Neighbor Discovery (NLT)

0

2

3

1

A

B

C

D

E

The NLT of Node A

0 C Yes -

1 B, E Yes -

2 D Yes -

3 - Yes -

beam No. neighbors available duration

10(ms)No

A node will record its neighbors’ info when it overhears any frames (RTS,CTS,data and ACK)

Neighbor Location Table (NLT)

The Finite State Machine of BT-DMAC

IDLEWF_DATA

WF_CTS

S_DATA

T1 T2

T3

T5

T6

T7

T8

T4

T9

Ti (E / A): the transition E: the trigger event A: the action of the transition

T1: data ready AND the beam for the destination available / send RTS and set timerT2: time out AND no CTS / T3: no CTS AND retry < RETRY_LIMIT / retransmit RTS T4: CTS received / BT on, set timerT5: ACK received OR retry >= MAX_RETRY / BT offT6: no ACK AND retry < MAX_RETRY/ retransmissionT7: DATA received / send ACK, BT offT8: time out / BT offT9: RTS received / send CTS, BT on, set timer

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A scenario

A

BTt(A,0)

0

12

3

0

12

3

D0

12

3

C

0

12

3

F0

12

3

E0

12

3

BTr(B,2)B

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The time diagram of BT-DMAC

A: Data transmission

B: Data transmission

DATARTS

CTS

ACK

BTt

BTr

A: Busy tone

B: Busy tone

hidden terminal due to unheard RTS/CTS

ACB

D

Deafness

BA

C

DATA

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Simulation Experiments

SimulatorGloMoSim 2.0 extension with Directional antennas

beamwidth 30 degrees

transmission range 376.78m

distance between each two nodes 360m

packet size 1460 byte

bandwidth 2Mbps

topology Linear

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Numeric result

0 1 2 3 4

0 1 2 3 4

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Throughput Comparison 1

r= 2 and p = 0.008 ( trts=tcts=tack=5τ, tdata= 100τ)

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Throughput Comparison 2

r= 2 and p = 0.008 ( trts=tcts=tack=5τ, tdata= 100τ)

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Conclusion

We propose BT-DMAC to attack the hidden terminals and deafness problems.

Simulation experiments prove the effectiveness of our proposed protocol.

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Thank you