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Cooperative Wireless Networking

Elza Erkip

Department of Electrical and Computer Engineering

Polytechnic Institute of New York University

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Motivation

• Future of internet: Wireless • Wireless channels

• Bandwidth limited• Limited battery life devices• Multi-user interference • Unreliable due to signal fading• Vulnerable to attacks

• Multimedia applications• High data rates• Error sensitive, delay intolerant

• How to overcome these obstacles?

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Cooperative Networking

• Wireless devices helping each other communicate with other devices or fixed infrastructure

• Cooperation provides a good solution to many of the problems arising in wireless systems

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How Does Cooperation Work?

• Wireless antennas transmit in all directions• Signals transmitted towards the base station can be

“overheard” at the relay• Relay processes this overheard information and re-

transmits towards the destination– Total resources (energy, bandwidth) are same as non-

cooperative case

• Base station processes signals from both mobiles

Mobile

Relay Base Station

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Benefits of Cooperation• Robustness to fading• Opportunistic use of network energy and

bandwidth• Higher data rates, fewer retransmissions so

less network delay• Higher signal quality• Lower total transmitted energy which reduces

interference and extends the battery life• Extended coverage

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Cooperative Networking Applications

• Currently a “hot” research topic• Also interest in industry, standardization

– 4G cellular

• Applications– Cellular

• Other mobiles can relay• Fixed (cheap) relays: Femtocells

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Cooperative Networking Applications

• WiFi• Enterprise networking• Vehicular ad-hoc networks

• Tactical networks

Cooperative Networking Applications

• Wireless Body Sensor Networks

8Figure from Sun et. Al, IEEE Wireless Communications Magazine, February 2010

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Poly’s Accomplishments• Poly has pioneered research in cooperative communications• IEEE paper award, cited extensively, top 10 downloaded article

in IEEE Xplore• A. Sendonaris, E. Erkip and B. Aazhang. User cooperation diversity-

Part I and Part II, IEEE TCOM 2003• One of the first papers looking at system level issues

– Top 100 downloaded article in IEEE Xplore• P. Liu, Z. Tao, Z. Lin, E. Erkip and S. Panwar. Cooperative wireless

communications: A cross-layer approach, IEEE Wireless Magazine, 2006.

• IEEE ICC Conference Best Paper• M. Yuksel and E. Erkip. Diversity-multiplexing tradeoff in half-duplex

relay systems, Proceedings of ICC, 2007. • One of the first groups to implement a cooperative networking

testbed

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Cooperative Networking @ Poly• Goal: A complete cooperative networking solution

– Establish the theory– Develop algorithms– Study applications– Implementation

• Multiple Poly faculty and students– Bertoni, Erkip, Knox, Memon, Panwar, Wang

• Government and industrial funding

Testbed Facilities

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Testbed Facilities

Experimental Results

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Conclusions• Cooperation: Paradigm shift in wireless

communications• Offers

– Spatial diversity– Higher throughput– Lower delay– Reduced energy consumption– Extended coverage– Higher quality multimedia– Improved security

• Cooperation in 4G cellular wireless standards• Many exciting projects studying cooperation at all

layers of the protocol stack– Theory + implementation

• Still many challenges