2. 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

3. 2 Outline Introduction What is Smart Antennas? Protocols Configuration Performance Conclusions

4. 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.

5. 4 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]

6. 5 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.

7. 6 Space Division Multiple Access(SDMA)

8. 7Antennas 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

9. 8 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 Antennas AB AB

10. 9 λ /2 λ λ λ Dipole Antennas Circular Antenna Antennas

11. 10 Antennas Dipole Antennas λ /2 磁場 Circular Antenna 磁場 λ /2 一圈 λ /2 2.4Ghz λ /2 = 6.2cm

12. 11 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

13. 12 MAC Protocols with Smart Antennas S D RTS DIFS CTS SIFS ACKRTSCTSACK SIFS OMNI-ModeARRAY-Mode NAV SHORT_NAV

14. 13 A RTS S_NAV B MAC Protocols with Smart Antennas B CTS NAV A RTS SHORT_NAVNAV Data Packet BA NAV Ack Packet AB

15. 14 MAC Protocols with Smart Antennas No Power Control (NPC) Data packet/ACK transmission following the RTS/CTS exchange is done at the same transmit power. P d = P t Global Power Control (GPC) DATA/ACK transmitter power is reduced to the same level. P d =  P t 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

16. 15 Configuration (1/4) S D RTS DIFS CTS SIFS ACKRTSCTSACK SIFS 10uS 4uS 14Byte18Byte14Byte500Byte 50m 25 Node Grid Network

17. 16 Configuration (2/4) 8 -3 1.5 -1.5 0 1 2 3 4 5 6 7 8 0123456 Poisson arrival process λ /2 λ

18. 17 Configuration (3/4) P r = P o d -n-n (1) SINR = G r G t P o / d n t-r Σ i-r nI i=1 G i G r P o / d + η n (2) Transmitter power T/R separation Path loss Receive Antenna gain Transmitter Antenna gain Receive power Signal to Interference plus noise power Interferencd Antenna gain Random noise power

19. 18 Configuration (4/4) -44dB 50M 500M SINR_min 10dB Random Noise Power -50dB -24dB -80dBm 34dB 54dB N1N2N15 50M 750M n=2 n=4.5 1000M

20. 19 Performance (1/4) Global Power Control γ =0.15 Global Power Control γ =0.5 Global Power Control γ =0.2 No Power Control 0.81.41.31.00.91.11.21.51.6 ×10 4 2.6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.7 Mean Delay (µsec) Nomalized Arrival Rate Fig.3. Optimal Power Control Ratio

21. 20 Performance (2/4) Fig.4. 25 Node Grid Network 1.41.20.60.40.81.01.61.8 ×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 Mean Delay (µsec) Nomalized Arrival Rate IEEE 802.11 DCF Local Power Control 24.77dB No Power Control Global Power Control γ =0.2

22. 21 Performance (3/4) 2.5 2.0 1.5 1.0 0.5 ×10 4 Mean Delay (µsec) 0 0 163245 Nomalized Arrival Rate Fig.5. 15 x 15 Grid IEEE 802.11 DCF Local Power Control 24.77dB No Power Control Global Power Control γ =0.2

23. 22 Performance (4/4) 1.20.6 2.0 1.8 1.2 1.0 0.6 ×10 4 Mean Delay (µsec) 0 0.2 0.4 0.8 1.4 1.6 0.20.4 0.81.0 Nomalized Arrival Rate Fig.6. 16 Element Antenna 1.61.42.01.8 IEEE 802.11 DCF Local Power Control 27.77dB No Power Control Global Power Control γ =0.1

24. 23 Conclusions Reduction in power is a key factor in improving the capacity of an ad hoc network 802.11b DCF No Power Control Global Power Control Local Power Control 25 node100 %130%170 %210 % 225 node100 %260 %475 %525 %