Energy-efficient schemes for on-demand relaying

This paper approaches the fading relay channel from an energy consumption perspective and proposes an on-demand scheme based on superposition coding and incremental redundancy (IR). The scheme aims at minimizing the relay's energy consumption, while maintaining a rate desired by the source. The source divides its message into two parts, which allows the destination to request only the missing part(s) from the relay. We derive the set of joint power and rate allocation optimal for energy. The proposed scheme only requires local SNR knowledge and is robust to feedback delay. Compared to classical IR, this scheme always provides energy gain, which can attain up to 50% (at each instant and on average), and helps decrease the outage probability.