Functional forwarding of channel state information

In large relay networks, the assumption of full and perfect channel knowledge at the destination is optimistic in practice. The fading coefficients are typically measured at the relays but not directly known at the destination. Traditionally, each fading coefficient is individually forwarded to the destination. However, it is often sufficient for the decoder to know only a function of the various channel states rather than the full information. We develop a general framework for forwarding channel state information in relay systems with local channel knowledge. We apply our framework to several networks and find that functional forwarding of channel state information can be attained much more efficiently than full forwarding.