1. Cross-layer Design in Wireless Mesh Networks Hu Wenjie Computer Network and Protocol Testing Laboratory, Dept. of Computer Science & Technology, Tsinghua Univ.

2. Saturday, February 16, 2008 Outline Introduction to the Wireless Mesh Networks Motivation of Cross-layer design Recent Cross-layer design schemes Negative consequences of Cross-layer design Conclusions

3. Saturday, February 16, 2008 Introduction to the Wireless Mesh Networks Centralized Wireless Networks Distributed Wireless Networks Wireless Mesh Networks Traditional Easy management Easy update Unbalanced load Small coverage area Large Coverage area Balanced load Dynamic topology Hard management

4. Saturday, February 16, 2008 Introduction to the Wireless Mesh Networks Mesh Routers: Infrastructure Almost stable No power limitation Multiple Wireless Interface Routing/Bridge/Gateway Mesh Clients: Mobile Battery powered One Wireless Interface Routing

5. Saturday, February 16, 2008 Motivation of Cross-layer design Unreliable of physical layer: Various wireless technology IEEE 802.11,802.16,3G various capacity, bit error rate Advanced physical technology Multiradio/multichannel, directional antenna, MIMO Conclusion1: MAC, routing, and transport protocols have to work together with the physical layer. A B

6. Saturday, February 16, 2008 Motivation of Cross-layer design Multi-hop: Accumulated effect Performance degradation Local vs. Global optimization MAC layer vs. Routing, Transport layer A B C D E Conclusion2: MAC, routing, and transport protocols need to work collaboratively among themselves.

7. Saturday, February 16, 2008 Cross-layer Design Schemes According to the relationship of different layers : 1.Loosely-coupled Use parameters in other protocol layers Dont totally abandon the transparency between layers Limited improvement 2.Tightly-coupled Different layers are optimized together Extreme: merge different protocol layers into one layer Better performance Lose protocol layer abstraction

8. Saturday, February 16, 2008 MAC/PHY Cross-layer Design PHY MAC Routing Transport Application TCP/IP protocol stack physical layer can provide: OFDM, UWB, multiradio/multichannel, MIMO, etc MAC layer can provide: The function to tune the parameters to achieve optimal performance

9. Saturday, February 16, 2008 Routing/MAC Cross-layer Design PHY MAC Routing Transport Application TCP/IP protocol stack The routing performance is poor if the MAC layer doesnt provide satisfying performance. The information in MAC layer, such as link quality, interference level, traffic load information and channel allocation, is also important to determine the best routing path.

10. Saturday, February 16, 2008 Transport/PHY Cross-layer Design PHY MAC Routing Transport Application TCP/IP protocol stack TCP has to use physical information to determine real congestion or poor quality in a link. When the link is congested, the physical layer can turn down the transmit power to avoid congestion. If the link quality is low, the physical layer can adjust coding rate or transmit power to enhance the quality.

11. Saturday, February 16, 2008 Negative Consequences of Cross-layer Design Reason: destroy the protocol layer abstraction Spaghetti design Incompatibility with existing protocols Difficulty in maintenance and management

12. Saturday, February 16, 2008 Conclusion Cross-layer design: Optimal performance Loss of good architecture TCP/IP protocol: Good architecture Low performance A New Protocol Stack!

13. Saturday, February 16, 2008 Thank you!