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 diversity
Coding and Interleaving
• Frequency diversity
CDMA, OFDM
• Spatial diversity
MISO, SIMO, MIMO
Interference
• TDMA
Graph Coloring
• Contention-based mechanisms
Aloha, CSMA, etc
• CDMA
Multiuser Detection (SIC)
Summary
Multipath
fading
Time diversity
Frequency
diversity
Interference
Spatial diversity
Building better bit pipes
Multipath fading
Opportunity
Opportunistic Communication
Cross-layer Wireless Resource Allocation
TDMA
Contentionbased schemes
CDMA+MD
Allocating bit pipes wisely
Can we exploit the
interference?
Can we exploit the interference?
• What is the basic characteristic of wireless
medium which causes the interference?
• Cooperative communication
• Cooperative diversity
Summary
Multipath
fading
Time diversity
Frequency
diversity
Interference
Spatial diversity
Building better bit pipes
Multipath fading
Opportunity
Opportunistic Communication
Cross-layer Wireless Resource Allocation
Contentionbased schemes
TDMA
CDMA+MD
Allocating bit pipes wisely
Broadcasting
Cooperation
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
Power
Time Savings
Non-cooperative
Cooperative
Energy Savings
Delay
Conclusion
• Cooperative Communication.
• Research Trends
• Coded-based Cooperation
• Capacity of Cooperative networks
Relay
S
relay
D
Coded Cooperation
• BC mode
– Relay can decode
– Destination may not
• MAC mode
– Relay re-encodes/transmits
– Source transmits
• New information
• Repeats previous information
– Destination decodes
correlation
Modeling and Mathematics
We
Mathematical Heavy
New
Capacity
Capacity
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
• Sk
reliable set of nodes that have information at kth stage
• U k set of nodes that will be added to reliable set in the next
transmission
Sk 1  Sk U k
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.