Power‐constrained, spectral efficiency‐optimal, green cooperative device‐to‐device communication systems

Abstract

The author consider a relay‐assisted, two hop, cooperative device‐to‐device (D2D) communication system where a source device S transmits data to a destination device D using a non‐regenerative cooperative relay whose average transmit power is constrained. For the cooperative D2D system, the author consider the problem of optimally adapting the relay gain as a function of fading gains of S – R and R – D links to maximise fading‐averaged spectral efficiency. The author derive the spectral efficiency‐optimal relay gain adaptation policy (SERGAP), which determines optimal gain for the relay, and, analyse the fading‐averaged spectral efficiency of SERGAP. To gain more insights, the author derive upper bounds on the average spectral efficiency, and, also investigate its asymptotic behaviour using an insightful analysis. Furthermore, the author extend the fading‐averaged analysis to a system having multiple relays. The author also present numerical results for single relay and multiple relay systems and benchmark the proposed policy's performance with conventional and suboptimal relaying policies. The author show that SERGAP delivers higher average spectral efficiency than conventional relaying policies. Finally, spectral efficiency‐optimal relay placement for the proposed policy is also investigated via simulations, and, the author find that it is different from the suboptimal relaying policies.