Cooperative Diversity Cooperative Diversity in Wireless Systemsin Wireless Systems

Elzbieta Beres

June 24th, 2005

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OutlineOutline

Nature of the Wireless Channel

Diversity – what is it and how does it help ?

MIMO Systems Traditional multi-antenna systems Cooperative diversity and relaying Challenges

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Attenuation in a Wireless ChannelAttenuation in a Wireless Channel

Large-scale Distance ~ (deterministic) Shadowing - Large obstructions (random)

Small-scale fading Many signal paths due to reflections Paths may add in phase or out of phase (Random)

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Wireless ChannelWireless Channel

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Spatial DiversitySpatial Diversity

Independent paths to the destination

Increases probability that at least one path is not in a low fade

Significantly improves performance

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Spatial Diversity – PerformanceSpatial Diversity – Performance

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Traditional MIMO SystemsTraditional MIMO Systems

Multiple antennas at receiver and transmitter

Not sure that multiple antennas can be implemented on mobiles

Cannot overcome shadowing

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Cooperative Diversity and RelayingCooperative Diversity and Relaying

Independent paths can be created using other terminals

Can also overcome shadowing!

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Half-duplex constraintHalf-duplex constraint

The relay must be assigned an additional orthogonal channel

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Main challengesMain challenges

How should relays send information? Amplify and forward? Decode and forward? Decode and re-encode?

How can multiple relays be incorporated into the system? How will they interact?

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Questions ?