Cooperative Communication Strategies for Sensor

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					 Cooperative Communication
Strategies for Sensor Networks



  Chulhan Lee, Sriram Vishwanath
System model




High throughput : Common messages
enable cooperation in the cluster-head
Decode-and-forward in a cluster-head
Duplexing (TDD/FDD) is used.
Single antenna system


        BC          Correlated MAC

 Combination of broadcast channel (BC)
 and correlated multiple access channel
 (correlated MAC).
BC and correlated MAC
                 (h1>h2)




Capacity bound slope is     Capacity bound slope is
less than 45°.              greater than 45°.
Using better channel only   Only using MISO channel
obtains sum capacity.       obtains sum capacity.
Three scenarios




Full cooperation    No cooperation      Limited Cooperation
Channel condition   Channel condition   General channel condition
                                        Power policy
Power policy        Power policy                  is obtained from
                                        intersection
Generalization: two antenna model




                   Cluster-head

 BC is hard problem since this is not degraded BC
 Common message W0 is necessary to generalize.
           : priorities of W0, W1, W2
BC




                      W0 is not necessary.
Capacity is achieved by dirty paper coding (DPC).
Encoding order: from higher priority to lower priority
information.
Sum-capacity occurs on the R0=0 plane.
Correlated MAC



                    only common information W0
Decoding order: higher priority decoding later.
The decoding order at correlated MAC is the
reverse of the encoding order at BC.
Sum-capacity occurs on R1=R2=0 line.
Sum-capacity




Sum-capacity is obtained at the intersection of BC and
correlated MAC capacity bound.
The farthest point from (0,0,0) in the intersection is the sum-
capacity point.
Conclusion

 Cooperation within cluster provides MIMO-
 like gains in throughput for the overall
 system.
 Intersection of BC and correlated MAC
 capacity region guides power distribution
 for information.