Energy-efficient power allocation scheme for DAS with adaptive modulation

This paper investigates the energy efficiency (EE) of distributed antenna system (DAS) with continuous-rate adaptive modulation (CAM) under different quality of service requirements, and develops adaptive power allocation (PA) schemes for DAS. Firstly, the EE for DAS with CAM is presented. By maximizing the EE subject to the maximum transmit power, target bit error rate (BER), and minimum spectral efficiency (SE) requirements, the optimized objective on PA is formulated. Based on this, a general form of optimal PA is derived by using the Karush-Kuhn-Tucker (KKT) conditions. Then, two cases are analyzed. One is that the SE equals the target one, and an efficient iterative algorithm to obtain the optimal PA is proposed. The other case is that the SE is larger than the target one, and an efficient method is derived to obtain the optimal number of active remote antennas. With the obtained optimal number, the closed-form power allocation is also derived by utilizing the Lambert function. The developed schemes include some existing schemes as special cases. Simulation results indicate the presented schemes are valid, can obtain the superior EE performance while meeting the target BER and minimum SE requirements.