Relaying in interference limited networks: Models, bounds, and strategies

Interference is inherent in wireless communication systems and can severely degrade communication rates. Relaying, on the other hand, is a well-known technique primarily used to provide significant rate improvements to point-to-point communications. In this dissertation, the impact of relaying in interference-limited networks is investigated. Depending on the relay's transmission and reception bands, various configurations are explored: the relay reception, or both reception and transmission, take place over orthogonal links (out-of-band relay reception and/or transmission), and the relay receives and transmits in the same band as the sources (in-band relay reception/transmission ). Novel relaying techniques, denoted by signal relaying, interference forwarding and interference cancelation, to manage interference in interference-limited multi-terminal networks are proposed.;To model and explore these interference-limited systems, initially, an interference channel (IC) with a relay is considered where the relay operates over an orthogonal band with respect to the underlying IC. The overall system is referred to as IC with an out-of-band relay (IC-OBR). The conditions under which signal relaying and/or interference forwarding operations ensure optimality in terms of capacity are identified. The optimality of signal relaying is shown to entail separability among the IC and the relay channel, exhibiting substantial reduction in encoding/decoding complexity. The essence of interference forwarding in addition to signal relaying in improving the communication rates is demonstrated and the capacities are established in special cases.;Next, the relay is assumed to transmit in the band of IC while reception is employed over the channels with orthogonal bands and finite capacities. This model is denoted by IC with an out-of-band reception/in-band transmission relay (IC-OIR). It is shown that in-band transmission by the relay uniquely facilitates the reduction of interference at the terminals through interference cancelation feature at the relay, which cannot be exploited by IC-OBR. An achievable scheme based on partial decode-and-forward transmission and dirty-paper coding at the relay is proposed. Outer bounds on the capacity region are obtained and shown to be tight for relatively large source-to-relay channel gains and the channel conditions named as mixed relay-interference conditions and very strong relay-interference conditions.;Finally, an interference channel assisted by a full-duplex relay that operates in the transmission band of the source-destination pairs is explored. An achievable scheme with rate-splitting at the sources and decode-and-forward (DF) transmission at the relay is obtained and compared with its time-division counterpart. Interference forwarding and cancelation operations are demonstrated to provide significant throughput gain depending on the network topology.