1. A new Cooperative Strategy for Deafness Prevention in Directional Ad Hoc Networks Andrea Munari, Francesco Rossetto, and Michele Zorzi University of Padova, Italy IEEE ICC 2007

2. Outline Introduction Related Work Antenna Model Cooperative MAC (CMAC) Simulation Conclusions

3. Introduction Wireless ad hoc networks are radio-based systems that do not need an access point or base station to operate. When antenna arrays are employed. Directional transmissions enable a spatial reuse of the channel.

4. Introduction Deafness A terminal is said to be deaf if it does not answer an RTS message addressed to it. A B RTS

5. Introduction Deafness in directional RTS A D E B C F I can’t hear anything.

6. Introduction In Omni-directional RTS A D E B C F I can’t send to B. I can’t send to B,C. I can’t send to B,C,D.

7. Related Work Circular RTS/CTS Mechanism (CRCM) RTS and CTS packets are broadcast omni- directionally by means of a sequence of directional transmissions. A B RTS CTS DATA

8. Motivation There is still some deafness problems in directional transmissions. A D E B C F I can’t hear anything. I can’t send to A. I can’t send to A,B. I can’t send to B,C. I don’t hear anything.

9. Goal CMAC proposes a cooperation scheme among nodes, trying to inform terminals that go back to idle mode after a transmission about communications that have started in the meantime.

10. Antenna Model Each node can decode more than one packets simultaneously, provided that they come from different directions. Each node can’t receive anything during the transmission.

11. Cooperative MAC (CMAC) CMAC employs three solutions to let the nodes have a fair image of their neighbors’ state Circular delivery of RTS and CTS. Multiple Receptions. Cooperation among nodes.

12. Cooperative MAC Cooperation among nodes The main cause of deafness is a mistaken idea of the network activity. This mechanism helps the nodes to know the new links built during the transmission. Each node maintains an internal table, called Communication Register (CR), where all the known ongoing communications are reported.

13. Cooperative MAC A D E B C F Node idTime Left A5 Node idTime Left A4 B10 Node idTime Left B10 Node idTime Left B6 Node idTime Left A5 I should be update A’CR. Node idTime Left B6 Node idTime Left A4 Node idTime Left B6 Collaboration frame

14. Simulation SimulatorOPNET (version 11.5) Parameters Nodes10 (in single hop) Area1500m x 1000m Antennas8 antennas Data rate1 Mbits/s Traffic ratePoison traffic at nominal rates of 8,16,25,50,100,150 packets/s Packet sizes RTS240 bits CTS240 bits Collaboration120 bits Data10240 bits ACK120 bits

15. CRCMMUDL-CMACB-CMAC Circular delivery of RTS/CTSOOOO Multiple receptionsOOO Cooperation among nodesOO The overhead of collaboration frames O Interference is generated by collaboration frames O The size of collaboration frames 120 bits (fixed) Optimal The low bound of CMAC The upper bound of CMAC MultiUser Detection

16. Simulation Link failures vs. load (10 nodes) Link Failures=

17. Simulation Power consumption vs. load (10 nodes)

18. Simulation Throughput vs. effective load (10 nodes) Throughput= Load=

19. Conclusion The cooperation in this paper is used for telling the nodes correct information. The impact of our solutions on multihop networks and routing is an interesting problem and is part of our future work.

20. Thank you~