1. Addressing Deafness and Hidden Terminal Problem in Directional Antenna Based Wireless Multi-hop Networks Anand Prabhu Subramanian and Samir R. Das {anandps, samir@cs.sunysb.edu} Computer Science Department Stony Brook University, NY, USA

2. Anand Prabhu Subramanian anandps@cs.sunysb.edu COMSWARE 2007 January 7-12, 2007 Outline Motivation – Why Directional Communication? Deafness Directional Hidden Terminal Problem Antenna Model CW-DMAC Design Performance Evaluation Summary

3. Anand Prabhu Subramanian anandps@cs.sunysb.edu COMSWARE 2007 January 7-12, 2007 Motivation - Capacity Problem in Multi-hop Wireless Networks Wireless Multi-hop Networks – Ad hoc Networks, Mesh Networks Data packets forwarded over multiple hops Wireless channel is a shared medium Capacity of multi-hop networks limited by wireless interference Directional communication can reduce interference

4. Anand Prabhu Subramanian anandps@cs.sunysb.edu COMSWARE 2007 January 7-12, 2007 Directional Antenna - Basics A Directional/Beam forming antenna has certain preferred transmit and receive directions Steerable beam vs switched beam Omni-directional Beam

5. Anand Prabhu Subramanian anandps@cs.sunysb.edu COMSWARE 2007 January 7-12, 2007 Directional Antenna - Benefits Directional Communication  Less energy in the undesired directions Better spatial reuse  More energy in the desired direction Longer Ranges More robust links Both higher spatial reuse and longer range can be simultaneously obtained

6. Anand Prabhu Subramanian anandps@cs.sunysb.edu COMSWARE 2007 January 7-12, 2007 Directional Communication Omni- Directional CommunicationDirectional Communication A B C D E F A B C D E F

7. Anand Prabhu Subramanian anandps@cs.sunysb.edu COMSWARE 2007 January 7-12, 2007 Directional Communication - Challenges Just adding a directional antenna is not enough New Challenges:  Direction to transmit  Deafness  Directional Hidden Terminal Problem  Broadcasting  And more …

8. Anand Prabhu Subramanian anandps@cs.sunysb.edu COMSWARE 2007 January 7-12, 2007 Deafness – Type I Destination engaged in communication X 1 2 4 3 B 1 2 4 3 A 1 2 4 3 Deafness

9. Anand Prabhu Subramanian anandps@cs.sunysb.edu COMSWARE 2007 January 7-12, 2007 Deafness – Type II Precautionary Deafness at the Receiver A 1 2 4 3 B 1 2 4 3 S 1 2 4 3 D 1 2 4 3 Deafness

10. Anand Prabhu Subramanian anandps@cs.sunysb.edu COMSWARE 2007 January 7-12, 2007 Directional Hidden Terminal Problem S 1 2 4 3 A 1 2 4 3 B 1 2 4 3 D 1 2 4 3 Collision - Due to unheard RTS/CTS packets

11. Anand Prabhu Subramanian anandps@cs.sunysb.edu COMSWARE 2007 January 7-12, 2007 Current Literature Many proposals in the past to solve deafness ko00infocom, choudhury02mobicom, choudhury04icnp, elbatt03wcnc, gossain04globecom, nasipuri00wcnc, sundaresan03mobihoc, takai02mobihoc These approaches use additional resources such as additional channels, radios or busy tones Directional hidden terminal problem not addressed

12. Anand Prabhu Subramanian anandps@cs.sunysb.edu COMSWARE 2007 January 7-12, 2007 Our Goal Solve both deafness and directional hidden terminal problem using  Single Channel  Single Radio Interface

13. Anand Prabhu Subramanian anandps@cs.sunysb.edu COMSWARE 2007 January 7-12, 2007 Antenna Model Switched beam antenna with N beams covering the entire 360 degrees Two modes of operation  Omni mode  Directional Mode Directional Gain = Omni Gain A

14. Anand Prabhu Subramanian anandps@cs.sunysb.edu COMSWARE 2007 January 7-12, 2007 Antenna Model 8 phased-array antenna elements Can form both omni- directional and directional beams Customizable beam pattern Beam switch time around 150 μs Directional gain = 15dBi Commercially available Directional Antenna

15. Anand Prabhu Subramanian anandps@cs.sunysb.edu COMSWARE 2007 January 7-12, 2007 Antenna Model Packet Transmission – either in omni or directional mode Packet Reception  When Idle – omni mode  When it detects a packet, does an azimuthal scan and goes to directional mode

16. Anand Prabhu Subramanian anandps@cs.sunysb.edu COMSWARE 2007 January 7-12, 2007 Assumptions Nodes are fairly static – (e.g. routers in Wireless Mesh Networks) Each node knows the direction (beam index) to its neighbor – Simple neighbor discovery protocol Nodes need not have an aligned axis

17. Anand Prabhu Subramanian anandps@cs.sunysb.edu COMSWARE 2007 January 7-12, 2007 CW-DMAC Design Type I deafness can be solved if transmitter/receiver can inform neighbors about their impending transmission. Type II deafness can be solved if the blocked receiver can somehow inform the transmitter that their transmission cannot take place without disturbing an ongoing transmission. Directional hidden terminal problem can be solved if the nodes do not miss any RTS/CTS packets in the neighborhood

18. Anand Prabhu Subramanian anandps@cs.sunysb.edu COMSWARE 2007 January 7-12, 2007 CW-DMAC Design RTS/CTS packets sent omni-directionally DATA/ACK packets sent directionally RTS/CTS packets are overloaded with the beam index of the intended DATA/ACK transmission Neighboring nodes set their DNAV tables appropriately depending on the beam index in the RTS/CTS packets Each neighboring node record this transmission in their neighborhood transmission table

19. Anand Prabhu Subramanian anandps@cs.sunysb.edu COMSWARE 2007 January 7-12, 2007 CW-DMAC Design X 1 2 4 3 B 1 2 4 3 A 1 2 4 3 Y 1 2 4 3 Aware of A’s transmission

20. Anand Prabhu Subramanian anandps@cs.sunysb.edu COMSWARE 2007 January 7-12, 2007 CW-DMAC Design There is a possibility of collision between omni-directionally sent RTS/CTS packets and DATA/ACK packets. We separate transmission of data packets and control packets in time Control window – added in RTS/CTS packets  Prevents collision between data and control packets  Allows multiple simultaneous transmissions in the neighborhood in different directions S 1 2 4 3 A 1 2 4 3 B 1 2 4 3 D 1 2 4 3

21. Anand Prabhu Subramanian anandps@cs.sunysb.edu COMSWARE 2007 January 7-12, 2007 CW-DMAC Design Adjustable control window  Small control window – less parallelism  Large control window – poor channel utilization To solve – deafness of type II  Negative CTS sent by blocked receivers  So the transmitter can cancel its transmission

22. Anand Prabhu Subramanian anandps@cs.sunysb.edu COMSWARE 2007 January 7-12, 2007 Performance Evaluation Simulation – Qualnet 3.7  8 beam directional antenna (45 degrees)  802.11b physical layer  11 Mbps data rate  Comparison between CW-DMAC and DMAC  30 nodes in an area of 1500m x 1500m

23. Anand Prabhu Subramanian anandps@cs.sunysb.edu COMSWARE 2007 January 7-12, 2007 Performance Evaluation - Deafness

24. Anand Prabhu Subramanian anandps@cs.sunysb.edu COMSWARE 2007 January 7-12, 2007 Deafness Ripple Effect

25. Anand Prabhu Subramanian anandps@cs.sunysb.edu COMSWARE 2007 January 7-12, 2007 Directional Hidden Terminal Problem

26. Anand Prabhu Subramanian anandps@cs.sunysb.edu COMSWARE 2007 January 7-12, 2007 Random Network - 30 nodes in 1500m x 1500m - 5 simultaneous flows - Deafness and directional hidden terminal problem cause performance degradation

27. Anand Prabhu Subramanian anandps@cs.sunysb.edu COMSWARE 2007 January 7-12, 2007 Summary Directional communication can reduce interference in multi-hop networks and improve capacity Studied various scenarios in which deafness and directional hidden terminal problem could occur Proposed a directional MAC protocol that solves both the problems using a single radio and single channel Simulations show the improvement when the both the problems are solved

28. Anand Prabhu Subramanian anandps@cs.sunysb.edu COMSWARE 2007 January 7-12, 2007 Thank you Questions ???