1 Ad Hoc Networks with Smart Antennas Using IEEE 802.11-Based Protocols Terence D.Todd Computer Engineering ICC 2002 Conference Nader S. Fahmy Department of Electrical Richie.Lin 2002/09
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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 %