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

Cross-layer Design in

Wireless Mesh Networks

Hu Wenjie

Computer Network and Protocol Testing Laboratory,

Dept. of Computer Science & Technology, Tsinghua Univ.

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

Saturday, February 16, 2008

Introduction to the Wireless Mesh Networks

Centralized Wireless Networks

Distributed Wireless Networks

mesh router

mesh client

mesh router

mesh router

mesh router

mesh router

mesh client

mesh client

mesh client

mesh client

mesh client＋

Wireless Mesh

Networks

Traditional •Easy

management

•Easy update

•Unbalanced load

•Small coverage area

•Large Coverage area

•Balanced load

•Dynamic topology

•Hard management

Saturday, February 16, 2008

Introduction to the Wireless Mesh Networks

mesh router

mesh client

mesh router

mesh router

mesh router

mesh router

mesh client

mesh client

mesh client

mesh client

mesh client

Mesh Routers:•Infrastructure•Almost stable•No power limitation•Multiple Wireless Interface•Routing/Bridge/Gateway

Mesh Clients:•Mobile•Battery powered•One Wireless Interface•Routing

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

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.

Saturday, February 16, 2008

Cross-layer Design Schemes

According to the relationship of different layers:

1. Loosely-coupled

Use parameters in other protocol layers

• Don’t 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

Saturday, February 16, 2008

MAC/PHY Cross-layer Design

PHY

MAC

Routing

Transport

Application

TCP/IP protocol

stackphysical layer can provide: OFDM, UWB, multiradio/multichannel, MIMO, etcMAC layer can provide: The function to tune the parameters to achieve optimal performance

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 doesn’t 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.

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.

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

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!

Saturday, February 16, 2008

Thank you!