Cooperative Communication

Xu Jiaming

Outline

• Introduction• Cooperative Routing• Power and Delay trade-off in Cooperative

Networks• Conclusion

Introduction

• Two fundamental aspects of Wireless Networks

multipath fading Interference

Multipath fading

• Time diversityCoding and Interleaving

• Frequency diversityCDMA, OFDM

• Spatial diversityMISO, SIMO, MIMO

Interference

• TDMAGraph Coloring

• Contention-based mechanismsAloha, CSMA, etc

• CDMAMultiuser Detection (SIC)

Summary

Building better bit pipes Allocating bit pipes wisely

Opportunistic Communication

Can we exploit the interference?

Cross-layer Wireless Resource Allocation

Can we exploit the interference?

• What is the basic characteristic of wireless medium which causes the interference?

• Cooperative communication• Cooperative diversity

Summary

Building better bit pipes Allocating bit pipes wisely

Opportunistic Communication

Cross-layer Wireless Resource Allocation

Cooperative Communication

Cooperative Networks

Cooperative Routing

• Cooperative communication is a cross-layer issues.

• Cooperative Routing• Reduce power consumption• Reduce Delay

What we learn?

• Power and Delay trade-off in Wireless Networks– Transmit the information to nodes far away

• low delay but high power consumption

– Transmit the information to nearby nodes• High delay but low power consumption

– Transmitter makes a choice according to current channel state and buffer occupancy.

Power and Delay Tradeoff Curve

Pow

er

Delay

Non-cooperative

Cooperative

Energy Savings

Time Savings

Conclusion

• Cooperative Communication.• Research Trends

• Coded-based Cooperation • Capacity of Cooperative networks

D

Relay

S relay

Coded Cooperation

• BC mode– Relay can decode– Destination may not

• MAC mode– Relay re-encodes/transmits– Source transmits

• New information• Repeats previous information

– Destination decodescorrelation

Modeling and Mathematics

We Capacity

New Capacity

Mathematical Heavy

ModelingMathematical Low

Cooperative Routing

• Cooperative communication is a cross-layer issues.

• Cooperative Routing in static wireless networks. Information is routed from s to d in a sequence of time slots Each time slot

• Broadcasting mode• Cooperation mode

Multistage decision problem

Cooperation Graph

• reliable set of nodes that have information at kth stage

• set of nodes that will be added to reliable set in the next transmission

kS

kU

1k k kS S U

Cooperative Routing benefits

• Restrict the cooperation to nodes along the optimal non-cooperative route.

• Energy savings

Alternative view toward Cooperative Routing

• Cooperative communication increases the transmission range.