A Directional MAC Protocol for Practical Smart Antennas

1. A Directional MAC Protocol for Practical Smart Antennas Yuya Takatsuka, Katsushiro Nagashima, Masaki Bandai and Takashi Watanabe Shiuzoka University GLOBECOM’06

2. Outline • Introduction • Related Works • Basic Evaluation • Causes of Interference • Proposed MAC Protocol • Performance Evaluations • Conclusions

3. Introduction • Attempting to use omni-directional antenna to achieve high throughput is a ineffective policy • Wasting a large portion of the network capacity. • To deal with this problem, smart or directional antenna technology may have various potentials. • There are some protocols have been proposed and they were evaluated using simulation with ideal antenna beam form.

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

5. Signal Background • If Signal Waves overlap with each other, they can communicate. D S S D

6. 2.CTS Location (S,D) 1.RTS Location (S) OC-mode (omni-directional area communication access mode) • No knowledge of location information • RTS/CTS/SOF (start of frame)/DATA/ACK S: Source D: Destination {A,B,C}: Neighbors B C S D A

7. 4.DATA 5.ACK 3.SOF Location (D) OC-mode • No knowledge of location information • RTS/CTS/SOF (start of frame)/DATA/ACK S: Source D: Destination {A,B,C}: Neighbors 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. B C S D A

8. Omni-NAV • The Omni-NAV is set to the neighboring nodes that receive either RTS only or CTS only. • The nodes which are set to Omni-NAV postpone the communication until the completion of SOF.

9. S D EC-mode (Extend area communication access mode) • The EC-mode is selected when the transmitter node has knowledge of location information of destination node by OC-mode communications. Two Hops

10. S D EC-mode (Extend area communication access mode) • RTS is transmitted with a high gain beam form and received with omni-directional beam form. 1. RTS Location (S) High Gain Beam Form

11. S D EC-mode (Extend area communication access mode) • CTS/DATA/ACK are transmitted and received with the directional beam form. 2.CTS Location (s) 3.DATA 4. ACK Normal Gain Beam Form

12. Smart Antenna • ESPAR (Electronically Steerable Passive Array Radiator)

13. Smart Antenna

14. Basic Evaluation • Simulation Parameters • Nodes: 100 • Area: 1500m * 1500m • Deployment: Random • Packets arrive: Poisson distribution with a mean value of λ • Packet size: 1460 bytes • Omni-directional range: 250m • Data Rate: 2Mbps • The destination node for each packet is chosen at random form two hop communication neighbors

15. Performance of Protocols

16. With Ideal Antenna

17. With Practical Antenna

18. DATA Receiving in OC-mode

19. DATA Receiving in EC-mode

20. Courses of Interference • Interference by transmission after Omni-NAV

21. Courses of Interference • Interference by transmission from the hidden terminals in OC-mode

22. Courses of Interference • Interference by transmission from the hidden terminals in EC-mode

23. Courses of Interference • Interference by directional hidden terminal problem

24. Proposed MAC Protocol • The proposed MAC protocol is based on SWAMP • Rotating the directional receive antenna beams • Transmitting NAV request frame • Transmission power control • OC-mode • EC-mode

25. Rotating the directional receive antenna beams • To solve the problems of B and C • In an idle state, each node rotates the directional receive antenna beam Stopping when hearing the tone Needing 200 microseconds to rotate one circle Spending 200 microseconds to send control packet tone R

26. NAV request frame • For the problem D, a NAV request frame is transmitted before receiving the DATA packet by the receiver node. • NAV request frame • Consist of RTR (Ready to Receive) in the OC-mode • Consist of CTS in the EC-mode

27. NAV request frame

28. Transmission Power Control

29. OC-mode • Two situations • Transmitter has no location information of destination node • When the destination node is located in the one hop communication area by omni-directional beam

30. RTS (Location information (Transmitter) , Transmission Power PtO) S D X Y CTS (Transmission Power PtO, NHDI, Location information (Receiver)) OC-mode RTR as the NAV request frame

31. SOF (Start of Frame) S D X Y RTR (Ready to Receive) OC-mode RTR as the NAV request frame

32. EC-mode • A transmitter has location information of the destination node Y X Y

33. Performance Evaluation

34. Performance Evaluation

35. Performance Evaluation

36. Conclusions • Evaluating the throughput of the previous work. • Pointing out interference problems and causes. • Providing the proposed MAC protocol with smart antenna • Deal with previous problems by rotating the directional receive antenna beam and transmitting the NAV request frame.