1. A Cooperative Diversity- Based Robust MAC Protocol in wireless Ad Hoc Networks Sangman Moh, Chansu Yu Chosun University, Cleveland State University Korea, Cleveland IEEE TPDS, March 2011 1

2. Outline O Introduction O Background O Cooperative Diversity MAC O Performance Evaluation O Conclusion and Future Work 2

3. Introduction O In wireless ad hoc networks, signal fading and interference are two major obstacles in realizing their full potential in delivering signals. O Cooperation among the nodes is considered critically important in addressing these problems. O It may be difficult to maximize the performance unless nodes are coordinated to cooperate at lower levels. O MAC- and PHY- layer 3

4. Introduction O Recently, some researches in developing cooperative MAC algorithms O Path-centric medium access O MAC-layer packet relaying O is determined in a proactive manner O is used to forward frames at higher bit rates O but not enhance the communication reliability, especially in interference-rich environment O Cooperative communication O enhance the link reliability 4

5. Introduction O Cooperative communication exploits diversity offered by multiple users, known as multiuser or cooperative diversity. O It dramatically improves bit error rate (BER). O More reliable transmission O Higher throughput 5

6. Background O Cooperative Diversity O Cooperative Diversity in Wireless Ad Hoc Networks 6

7. Cooperative Diversity O Two types of cooperative diversity algorithms O Repetition-based O Amplify-and-forward O Decode-and-forward O Space-time-coded O Distributed space-time coding (DSTC) O Space-time coding (STC) (multiantenna system) O Space-time block coding (STBC) (multiantenna system) 7

8. DSTC 8

9. Cooperative Diversity in Wireless Ad Hoc Networks O Azgin et al. proposed Cooperative MAC (C- MAC) and the corresponding routing protocols for wireless ad hoc network. (GlobeCom 2005) O Relaying start (RS) O Relay acknowledgement (RA) O Relay broadcasting (RB) O Transmission start (TS) O RTS-CTS-RS-RA-RB-TS-ACK 9

10. Cooperative Diversity MAC O Overview 10

11. A Simple Cooperative scheme O The authors proposed in ICC 2007. O Based on DCF of the IEEE 802.11 standard O If a primary link is reliable enough to successfully transmit frames, no cooperative transmission is enabled. O If it fails, the sender retransmits the frame but cooperatively with its partner O When to cooperate 11

12. A case for simple scheme 12

13. Problems of simple scheme O Twice longer than that without cooperation O An RTS failure can be due to collisions/interference from other nodes’ communication O The RTS/CTS exchange effectively eliminates the problem associated with “the hidden terminals”. 13

14. Cooperative Diversity MAC 14

15. State transition diagrams Sender Receiver Partner 15

16. Partner Selection and Its Propagation O Every node proactively selects its partner by monitoring or overhearing its neighbors with respect to link quality. O Measure and record the link quality while receiving a frame O The neighbor with the best link quality among all neighbors is chosen as its partner. 16

17. Why choose the neighbor with the best link quality? O Three reasons behind this choice O Communication between a node and its partner must be highly reliable. O A partner with the best link quality is most probably the closest node. O It ensures that the sender and the partner share the same communication environment so that they can make a consistent decision on cooperation. 17

18. Performance Evaluation O Using ns-2 simulator O 50 mobile nodes move over a square area of 300X1500 m 2 O Each simulation runs for 900 seconds. O Source-destination pairs are randomly selected. O Mobile nodes are assumed to move randomly with the node speed of 0-5 m/sec O Pause time between moves varies from 0 to 900 seconds. 18

19. Performance Comparison This is due to the complex interplay among MAC- and routing-layer protocols in MANET environment 19

20. Overhead and cooperation efficiency 20

21. Impact of environment noise 21

22. Effect of network traffic on packet delivery ratio 22

23. Conclusions and Future Work O This paper proposed CD-MAC and discusses design issues and performance benefits in wireless ad hoc network. O When a communication link is unreliable, a sender transmits its signal together with its partner delivering the signal more reliably. O As a future work, exploiting cooperative diversity based on multichannel interfaces will be investigated. 23