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

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

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

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

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

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

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

DSTC 8

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

Cooperative Diversity MAC O Overview 10

A Simple Cooperative scheme O The authors proposed in ICC O Based on DCF of the IEEE 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

A case for simple scheme 12

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

Cooperative Diversity MAC 14

State transition diagrams Sender Receiver Partner 15

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

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

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

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

Overhead and cooperation efficiency 20

Impact of environment noise 21

Effect of network traffic on packet delivery ratio 22

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