Using Directional Antennas for Using Directional Antennas for Medium Access Control in Ad Medium Access Control in Ad Hoc NetworksHoc Networks

Romit Roy Choudhury, Xue Yang, Romit Roy Choudhury, Xue Yang, Ram RamanathanRam Ramanathan. . and Nitin H. Vaidyaand Nitin H. Vaidya

University of lllinois at Urbana-ChampaignUniversity of lllinois at Urbana-Champaign

MOBICOM 2002

OutlineOutline IntroductionIntroduction Problems with Basic DMACProblems with Basic DMAC Multi-Hop RTS MAC ProtocolMulti-Hop RTS MAC Protocol Simulation Simulation Future work & ConclusionFuture work & Conclusion

IntroductionIntroductionAntenna ModelAntenna Model

Assumed antenna system Assumed antenna system Omni antennaOmni antenna

Tx/Rx from all directions (360 degrees)Tx/Rx from all directions (360 degrees) Directional antennaDirectional antenna

Can point its main lobe towards Can point its main lobe towards any specified dirany specified directionection

Do not consider Do not consider power controlpower control Fixed beamwidth Fixed beamwidth

Introduction Introduction Antenna ModelAntenna Model

A

Directional modeOmni mode

B

Benefits of directionalityBenefits of directionality Spatial Spatial reusereuse Higher transmission Higher transmission rangerange

Problems with Basic DMACProblems with Basic DMAC Hidden terminal problemsHidden terminal problems

Hidden terminal due to asymmetry in gainHidden terminal due to asymmetry in gain

BE FARTSCTS DATARxRTS

Problems with Basic DMACProblems with Basic DMAC

DeafnessDeafness

A

B

DC

DATADATA

DATA

Multi-Hop RTS MAC ProtocolMulti-Hop RTS MAC Protocol

Protocol Description : Multi-Hop RTSProtocol Description : Multi-Hop RTS Direction-Omni (DO) NeighborDirection-Omni (DO) Neighbor Direction-Direction (DD) NeighborDirection-Direction (DD) Neighbor

C D

TX RX

DD Neighbor

C D

TX RX

DO Neighbor

CTS

RTS

RTS

Multi-Hop RTS MAC ProtocolMulti-Hop RTS MAC Protocol

D

G

BRTS

F

C

RxDATA RXA

Simulation ResultsSimulation Results

SimulationSimulation

Future Work & Future Work & ConclusionConclusion

Rely lessRely less on the upper layers for beamfor on the upper layers for beamforming information ming information

ReplaceReplace the omni mode operation (tone) the omni mode operation (tone) Performance of the system improve in terPerformance of the system improve in ter

ms of aggregate ms of aggregate throughputthroughput and end-to-e and end-to-end nd delaydelay

Thank You !!Thank You !!

Problems with Basic DMACProblems with Basic DMAC Hidden terminal problemsHidden terminal problems

Hidden terminal due to unheard RTS/CTSHidden terminal due to unheard RTS/CTS

D

B FEDATA RTSCTS DATA

DATA