A Directional MAC Protocol for A Directional MAC Protocol for Practical Smart AntennasPractical Smart Antennas

Yuya Takatsuka, Katsushiro Nagashima, Yuya Takatsuka, Katsushiro Nagashima, Masaki Bandai and Takashi WatanabeMasaki Bandai and Takashi Watanabe

Shiuzoka UniversityShiuzoka University

GLOBECOM’06GLOBECOM’06

OutlineOutline

IntroductionIntroduction Related WorksRelated Works Basic EvaluationBasic Evaluation Causes of InterferenceCauses of Interference Proposed MAC Protocol Proposed MAC Protocol Performance EvaluationsPerformance Evaluations ConclusionsConclusions

IntroductionIntroduction

Attempting to use omni-directional antenna to acAttempting to use omni-directional antenna to achieve high throughput is a ineffective policyhieve high throughput is a ineffective policy Wasting a large portion of the network capacity.Wasting a large portion of the network capacity.

To deal with this problem, smart or directional anTo deal with this problem, smart or directional antenna technology may have various potentials.tenna technology may have various potentials.

There are some protocols have been proposed aThere are some protocols have been proposed and they were evaluated using simulation with nd they were evaluated using simulation with ideideal antenna beam formal antenna beam form. .

Related WorksRelated Works

SWAMP (Smart Antennas Based Wider-range SWAMP (Smart Antennas Based Wider-range Access MAC Protocol, ICC 2004) based on Access MAC Protocol, ICC 2004) based on IEEE 802.11 DCF is composed of two access IEEE 802.11 DCF is composed of two access modes.modes. OC-mode (Omni-directional area Communication OC-mode (Omni-directional area Communication

access mode) access mode) EC-mode (Extend area Communication access mode)EC-mode (Extend area Communication access mode)

Signal BackgroundSignal Background

If Signal Waves overlap with each other, If Signal Waves overlap with each other, they can communicate.they can communicate.

S DS D

OC-mode OC-mode (omni-directional area communication access mode)(omni-directional area communication access mode)

No knowledge of location information No knowledge of location information RTS/CTS/RTS/CTS/SOF (start of frame)SOF (start of frame)/DATA/ACK/DATA/ACK

A S B D C

S: Source D: Destination

{A,B,C}: Neighbors

S: Source D: Destination

{A,B,C}: Neighbors

1.RTSLocation (S)

2.CTSLocation (S,D)

OC-modeOC-mode

No knowledge of location information No knowledge of location information RTS/CTS/RTS/CTS/SOF (start of frame)SOF (start of frame)/DATA/ACK/DATA/ACK

A S B D C

S: Source D: Destination

{A,B,C}: Neighbors

S: Source D: Destination

{A,B,C}: Neighbors

3.SOFLocation (D)

4.DATA5.ACK

SWAMP requires the additional control frame SOF (Start Of Frame). Every node maintains an NHDI (Next Hop Direction Information) table with one entry for another node that can be obtained from NHDI in either CTS or SOF. Also note that the NHDI table of a node contains other nodes which the node cannot communicate directly with, which the node can communicate indirectly with by multi-hopping with an omni-directional beam, and which the node can communicate directly with a high gain directional beam to point their direction.

Omni-NAVOmni-NAV The Omni-NAV is set to the neighboring nodes that The Omni-NAV is set to the neighboring nodes that

receive either RTS only or CTS only. receive either RTS only or CTS only. The nodes which are set to Omni-NAV postpone the The nodes which are set to Omni-NAV postpone the

communication until the completion of SOF.communication until the completion of SOF.

EC-mode EC-mode (Extend area communication access mode)(Extend area communication access mode)

The EC-mode is selected when the transmitter The EC-mode is selected when the transmitter node has knowledge of location information of node has knowledge of location information of destination node by OC-mode communications.destination node by OC-mode communications.

S D

Two Hops

EC-mode EC-mode (Extend area communication access mode)(Extend area communication access mode)

RTS is transmitted with a high gain beam form aRTS is transmitted with a high gain beam form and received with omni-directional beam form.nd received with omni-directional beam form.

S D

1. RTSLocation (S)

High Gain Beam Form

EC-mode EC-mode (Extend area communication access mode)(Extend area communication access mode)

CTS/DATA/ACK are transmitted and received CTS/DATA/ACK are transmitted and received with the directional beam form.with the directional beam form.

S D

Normal Gain Beam Form

2.CTSLocation (s)3.DATA

4. ACK

Smart AntennaSmart Antenna

ESPAR (Electronically Steerable Passive ESPAR (Electronically Steerable Passive Array Radiator)Array Radiator)

Smart AntennaSmart Antenna

Basic Evaluation Basic Evaluation

Simulation ParametersSimulation Parameters Nodes: 100Nodes: 100 Area: 1500m * 1500mArea: 1500m * 1500m Deployment: RandomDeployment: Random Packets arrive: Poisson distribution with a mean value Packets arrive: Poisson distribution with a mean value

of λof λ Packet size: 1460 bytesPacket size: 1460 bytes Omni-directional range: 250mOmni-directional range: 250m Data Rate: 2MbpsData Rate: 2Mbps The destination node for each packet is chosen at ranThe destination node for each packet is chosen at ran

dom form two hop communication neighborsdom form two hop communication neighbors

Performance of ProtocolsPerformance of Protocols

With Ideal AntennaWith Ideal Antenna

With Practical AntennaWith Practical Antenna

DATA Receiving in OC-modeDATA Receiving in OC-mode

DATA Receiving in EC-modeDATA Receiving in EC-mode

Courses of InterferenceCourses of Interference

A.A. Interference by transmission after Omni-Interference by transmission after Omni-NAVNAV

Courses of InterferenceCourses of Interference

B.B. Interference by transmission from the hidden Interference by transmission from the hidden terminals in OC-modeterminals in OC-mode

Courses of InterferenceCourses of Interference

C.C. Interference by transmission from the hidden Interference by transmission from the hidden terminals in EC-modeterminals in EC-mode

Courses of InterferenceCourses of Interference

D.D. Interference by directional hidden terminal Interference by directional hidden terminal problemproblem

Proposed MAC ProtocolProposed MAC Protocol

The proposed MAC protocol is based on The proposed MAC protocol is based on SWAMPSWAMP Rotating the directional receive antenna Rotating the directional receive antenna

beamsbeams Transmitting NAV request frameTransmitting NAV request frame Transmission power controlTransmission power control OC-modeOC-mode EC-mode EC-mode

Rotating the directional receive Rotating the directional receive antenna beamsantenna beams

To solve the problems of B and CTo solve the problems of B and C In an idle state, each node rotates the In an idle state, each node rotates the

directional receive antenna beamdirectional receive antenna beam

Needing 200 microsecondsto rotate one

circleSpending 200 microseconds to send control

packet tone

Stopping when

hearing the tone

R

NAV request frameNAV request frame

For the problem D, a For the problem D, a NAV request frameNAV request frame is is transmitted before receiving the DATA transmitted before receiving the DATA packet by the receiver node.packet by the receiver node.

NAV request frameNAV request frame Consist of RTR (Ready to Receive) in the OC-Consist of RTR (Ready to Receive) in the OC-

modemode Consist of CTS in the EC-modeConsist of CTS in the EC-mode

NAV request frameNAV request frame

Transmission Power ControlTransmission Power Control

OC-modeOC-mode

Two situationsTwo situations Transmitter has no location information of desTransmitter has no location information of des

tination nodetination node When the destination node is located in the oWhen the destination node is located in the o

ne hop communication area by omni-directionne hop communication area by omni-directional beamal beam

OC-modeOC-mode

RTR as the NAV request

frame

S D

XY

RTS (Location information (Transmitter) , Transmis

sion Power PtO)

CTS (Transmission Power PtO, NHDI, Location information (Receiv

er))

OC-modeOC-mode

RTR as the NAV request

frame

S D

XY

SOF (Start of Frame)

RTR (Ready to Receive)

EC-modeEC-mode

A transmitter has location information of A transmitter has location information of the destination node the destination node

X

Y

Y

Performance EvaluationPerformance Evaluation

Performance EvaluationPerformance Evaluation

Performance EvaluationPerformance Evaluation

ConclusionsConclusions

Evaluating the throughput of the previous Evaluating the throughput of the previous work.work.

Pointing out interference problems and Pointing out interference problems and causes.causes.

Providing the proposed MAC protocol with Providing the proposed MAC protocol with smart antennasmart antenna Deal with previous problems by rotating the Deal with previous problems by rotating the

directional receive antenna beam and directional receive antenna beam and transmitting the NAV request frame.transmitting the NAV request frame.