Relay channel

In information theory, a relay channel is a probability model on the communication between a sender and a receiver aided by one or more intermediate relay nodes. It is a combination of the broadcast channel (from sender to relays and receiver) and multiple access channel (from sender and relays to receiver).

General discrete-time memoryless relay channel

A discrete memoryless single-relay channel can be modelled as four finite sets, $X\_1,\; X\_2,\; Y\_1,$ and $Y$, and a conditional probability distribution $p(y,y\_1|x\_1,x\_2)$ on these sets. The probability distribution of the choice of symbols selected by the encoder and the relay encoder is represented by $p(x\_1,x\_2)$.

o------------------o
Relay Encoder
o------------------o A
y1 x2
Vo---------o x1 o------------------o y o---------o
Encoder |--->| p(y,y1|x1,x2) |--->| Decoder
o---------o o------------------o o---------o

Degraded relay channel

Such a relay channel is said to be degraded if "y" depends on $x\_1$ only through $y\_1$ and $x\_2$, i.e., $p(y\; |\; x\_1,\; x\_2,\; y\_1)\; =\; p(y\; |\; x\_2,\; y\_1)$.

Reversely degraded relay channel

Feedback relay channel

Relay without delay channel

References

* Thomas M. Cover and Abbas El Gamal, " [http://yreka.stanford.edu/~cover/papers/transIT/0572cove.pdf Capacity theorems for the relay channel] ," " IEEE Transactions on Information Theory" (1979), pp. 572-584

External links

* Many resources on the Relay Channel and Cooperative Communications are available at " [http://utdallas.edu/~ramy/relaying.htm] ," - from Ramy Medhat Tannious webpage - UT Dallas.