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Ad Hoc Networks with Smart Antennas Using

IEEE 802.11-Based Protocols

Terence D.ToddComputer

Engineering

ICC 2002 Conference

Nader S. Fahmy

Department of Electrical

Richie.Lin 2002/09

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OutlineIntroductionWhat is Smart Antennas?ProtocolsConfigurationPerformanceConclusions

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Introduction (1/3)Introduction (1/3)

Ad hoc network may be much more geographically distributed with many partially overlapping radio coverage areas.May be a greater potential for spatial reuse of the transmission medium.Where increased spatial capacity is available, the protocols should be able to exploit it.

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Introduction (2/3)References

Low-cost adaptive antenna technologies have appeared. [1]Non-interfering due to the high degree of selectivity. [2]Use an IEEE 802.11-style RTS/CTS exchange with omni-directional transmission first.Physical layer parameters such as transmit power [3] and transmission rate [4] .RTS/CTS exchange is used to determine which of the ( 4) sectors should be used at the source and destination [5]

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Introduction (3/3)References

MAC protocol using directive antennas . Uses GPS to determine which sector should be used to communicate with a given destination [6]Smart antennas have also been used at the access point by the IEEE 802.11 PCF [7] ,Increases in capacity were obtained using multi-beam space division multiple access(SDMA) under control of the basestation.

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Space Division Multiple Access(SDMA)

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AntennasAntennas

前置放大約放大一千倍 (數十 dBm)

功率放大約放大數十倍 (10dBn)

接收靈敏度 發射增益

天線增益場型

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天線絕對增益 ( dBi ) ＝ 10 ㏒

理想天線所需發射的功率

待測天線的發射功率

AntennasAntennas

A B

A B

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λ/2λ/2

λ/2λ/2

Dipole Antennas

Circular Antenna

AntennasAntennas

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AntennasAntennas

Dipole Antennas

λ/2

磁場

Circular Antenna

磁場

λ/2一圈

λ/2

2.4Ghz λ/2 = 6.2cm

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Smart Antennas

微波工程 --> 天線工程 相列天線 Smart天線

單根天線場型多根天線組成的場型天線與天線的距離天線和天線間的相位差各天線的發射功率

Phase Array Antennas

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MAC Protocols with Smart Antennas

S

DRTS

DIFS

CTS

SIFS

ACKRTS CTS ACK

ACK ACK

SIFS

SIFS

OMNI-Mode ARRAY-Mode

NAVSHORT_NAV

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ARTS

S_NAV

B

MAC Protocols with Smart Antennas

BCTS

NAV

ARTS

SHORT_NAV NAV

Data PacketBA

NAV

Ack Packet A B

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MAC Protocols with Smart AntennasMAC Protocols with Smart Antennas

No Power Control (NPC)Data packet/ACK transmission following the RTS/CTS exchange is done at the same transmit power. Pd = Pt

Global Power Control (GPC)DATA/ACK transmitter power is reduced to the same level. Pd = Pt

Local Power Control (LPC)Nodes use the values of the received RTS/CTS power levels to compute how much power reduction is required.

Power control variantes

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Configuration (1/4)

S

D RTS

DIFS

CTS

SIFS

ACKRTS CTS ACK

ACK ACK

SIFS

SIFS10uS 4uS

14Byte18Byte 14Byte500Byte

50m

50m

25 Node Grid Network

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Configuration (2/4)

8-3

1.5

-1.5

0

1

2

3

4

5

6

7

8

0 1 2 3 4 5 6

Poisson arrival process

λ/2

λ/2

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Configuration (3/4)

Pr = Pod-n (1)

SINR =GrGtPo / d

n

t-r

Σ i-rnI

i=1GiGrPo / d + ηn

(2)

Transmitter power

T/R separation

Path loss

Receive Antenna gain

TransmitterAntenna gain

Receive power

Signal to Interference plus noise power Interferencd

Antenna gain

Random noise power

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Configuration (4/4)

-44dB

50M500M

SINR_min 10dB

Random Noise Power -50dB

-24dB

-80dBm

34dB

54dB

N1 N2 N15

50M

750M

n=2

n=4.5

1000M

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Performance (1/4)

Global Power Control γ =0.15

Global Power Control γ =0.5

Global Power Control γ =0.2No Power Control

0.8 1.41.31.00.9 1.1 1.2 1.5 1.6

×10 4

2.6

2.4

2.22.0

1.8

1.61.4

1.2

1.0

0.80.6

0.4

0.7

Mea

n D

elay

(µ

sec)

Nomalized Arrival Rate

Fig.3. Optimal Power Control Ratio

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Performance (2/4)

Fig.4. 25 Node Grid Network

1.41.20.60.4 0.8 1.0 1.6 1.8

×10 4

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0 0.2

Mea

n D

elay

(µ

sec)

Nomalized Arrival Rate

IEEE 802.11 DCF

Local Power Control 24.77dBNo Power Control

Global Power Control γ =0.2

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Performance (3/4)2.5

2.0

1.5

1.0

0.5

×10 4

Mea

n D

elay

(µ

sec)

00 1 632 4 5

Nomalized Arrival Rate

Fig.5. 15 x 15 Grid

IEEE 802.11 DCF

Local Power Control 24.77dBNo Power Control

Global Power Control γ =0.2

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Performance (4/4)

1.20.6

2.0

1.8

1.2

1.0

0.6

×10 4

Mea

n D

elay

(µ

sec)

00.2

0.4

0.8

1.4

1.6

0.2 0.4 0.8 1.0

Nomalized Arrival Rate

Fig.6. 16 Element Antenna

1.61.4 2.01.8

IEEE 802.11 DCF

Local Power Control 27.77dB

No Power ControlGlobal Power Control γ =0.1

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Conclusions

Reduction in power is a key factor in improving the capacity of an ad hoc network

802.11bDCF

No Power Control

Global Power Control

Local Power Control

25 node 100 % 130% 170 % 210 %

225 node

100 % 260 % 475 % 525 %