A Converse for the Wideband Relay Channel with Physically Degraded Broadcast
The authors investigate the multipath fading relay channel in the limit of a large bandwidth, and in the non-coherent setting, where the channel state is unknown to all terminals, including the relay and the destination. They derive a lower bound on the capacity by proposing and analyzing a peaky frequency binning scheme. The achievable rate obtained coincides with the block-Markov lower bound on the capacity of the wideband frequency-division Gaussian relay channel. When the broadcast channel is physically degraded, this achievable rate meets the cut-set upper-bound, and thus reaches the capacity of the non-coherent wideband multipath fading relay channel.