  A relay channel with orthogonal components that is affected by an
interference signal that is noncausally available only at the source is
studied. The interference signal has structure in that it is produced by
another transmitter communicating with its own destination. Moreover, the
interferer is not willing to adjust its communication strategy to minimize the
interference. Knowledge of the interferer's signal may be acquired by the
source, for instance, by exploiting HARQ retransmissions on the interferer's
link. The source can then utilize the relay not only for communicating its own
message, but also for cooperative interference mitigation at the destination by
informing the relay about the interference signal. Proposed transmission
strategies are based on partial decode-and-forward (PDF) relaying and leverage
the interference structure. Achievable schemes are derived for discrete
memoryless models, Gaussian and Ricean fading channels. Furthermore, optimal
strategies are identified in some special cases. Finally, numerical results
bring insight into the advantages of utilizing the interference structure at
the source, relay or destination.
