C. Li, H. J. Yang*, F. Sun, J. M. Cioffi, and L. Yang, “Approximate Closed-Form Energy Efﬁcient PA for MIMO Relaying Systems in the High SNR Regime,” IEEE Communications Letters, vol 18, no. 8, pp. 1367-1370, Aug. 2014.
Energy efficient power coefficients at the relay are derived in a closed-form expression for the green multi-input–multioutput relaying system in the high signal-to-noise ratio (SNR) regime, where the objective is to maximize the energy efficiency (EE), which is defined by the ratio of the spectral efficiency (SE) to total power consumption, with a minimum SE requirement under practical power consumption models. In particular, we derive closed-form solutions using the high SNR approximation, which turn out to be different from the water-filling solution. Simulation results show that the proposed solution nearly achieves the optimal EE in all SNR regimes.