A relay channel with orthogonal components in which the destination is affected by an interference signal that is non-causally 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.
With a single dominating interferer, interference structure can be utilized. This was recognized in @cite_18 , where a scenario in which a transmitter-receiver pair communicates in the presence of a single interferer is studied. It is shown therein that using GP coding, and hence treating the interference as if it were unstructured, it is generally suboptimal and with joint decoding at the destination can be beneficial @cite_29 . This aspect is further studied in @cite_28 for a MAC with structured interference available at one encoder, in @cite_3 for a Gaussian relay channel with an out-of-band relay and in @cite_27 for a cognitive Z-interference channel, where extensions of the techniques proposed in @cite_18 are investigated.
@cite_18 @cite_28 @cite_29 @cite_3 @cite_27
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Motivated by cognitive radio applications, we consider mitigating the effect of interference by exploiting known properties about its signal structure. Specifically, we analyze communication between a source and destination with an interferer that induces random variations in the source-destination channel. The interferer transmits a sequence chosen uniformly from a randomly generated codebook, which has an i.i.d. structure, or a superposition structure. It is assumed that both the encoder and decoder know the interferer's codebook. We first provide a definition of capacity for these settings. When the encoder knows the interferer's message noncausally, it can use Gel'fand-Pinsker (GP) encoding to precode against interference. Alternatively, it can encode by taking into account that the interference is a codeword, to enable the decoder to decode both messages. It is demonstrated by an example that the latter can outperform GP encoding. Two upper bounds to the performance of this channel are then presented. Next, a more realistic scenario is considered in which the interference is learned at the cognitive encoder causally through a noisy channel. It is shown that for the case of i.i.d. generated interference, this information has no value. In contrast, when the interference is a codeword from an i.i.d. generated codebook, this fact can be exploited to obtain higher rates between the cognitive pair. 1Consider an additive Gaussian noise channel affected by an additive interference sequence, taken from a given codebook, which is known non-causally at the transmitter (e.g., via prior decoding). It is known that in this case optimal performance is attained by Dirty Paper Coding, which treats the interference signal as unstructured. In other words, for this example, the knowledge of the specific interferer's codebook at the decoder is not useful in terms of capacity. In this paper, two variations of this basic scenario are presented in which treating interference as unstructured is instead generally suboptimal. In the first case, a second encoder of the source message is present in the system that is not aware of the interferer's sequence, and source and interference messages are uncorrelated; In the second case, the sources encoded by the informed transmitter and interferer are correlated (and an uninformed encoder may or may not be present). Results are given in terms of conditions for achievability for both discrete and Gaussian models of the scenarios discussed above, and corroborated by numerical results. Optimal strategies are also identified in special cases. The conclusions herein point to the importance of exploiting the interfererence structure in multiterminal and source-channel coding scenarios. We consider one-sided interference channel with two independent source-destination pairs, and a cognitive relay with only a link to the destination that observes interference. We first assume the relay non-causally obtains the signal messages (message cognitive) whereas the sources do not cooperate, and provide a general achievable rate region for the Gaussian case. We further analyze a more realistic set-up where instead of source messages, the relay knows the transmitted signals of both sources and is unaware of the codebooks. We investigate the achievable region under this signal cognitive assumption and further obtain a converse, thereby the capacity region under strong relay-interference conditions. Our results suggest that while relaying is usually utilized as an effective technique for boosting received signal quality, in the presence of interference, an equally important task of the relay is to manage the interference. We consider a relay channel in the presence of interference which is non-causally available only at the source. The interference signal may have structure, for example it could come from another source communicating with its own destination. However, the external interferer is not willing to adjust its communication strategy to minimize the interference and is considered to be fixed. Two approaches are possible to mitigate the interference: exploiting the structure or treating the interference as unstructured. Using these approaches, we establish bounds for the Gaussian relay channel with orthogonal components and discuss to the importance of exploiting the interference structure in multi-terminal scenarios. We study the discrete memoryless Z-interference channel where the transmitter of the pair that suffers from interference is cognitive. We first provide an outer bound on the capacity region of this channel. We then show that, when the channel of the transmitter-receiver pair that does not experience interference is deterministic and invertible, our proposed outer bound matches the best known inner bound. The obtained results imply that in the considered channel, superposition encoding at the noncognitive transmitter as well as Gel'fand-Pinsker encoding at the cognitive transmitter is needed in order to minimize the impact of interference. As a byproduct of the obtained capacity region, we obtain the capacity under the generalized Gel'fand-Pinsker setting where a transmitter-receiver pair communicates in the presence of interference noncausally known at the encoder.