Suboptimal energy efficient power allocation scheme for distributed antenna system in Rayleigh fading channel

In this paper, the energy efficiency (EE) of distributed antenna system (DAS) with multiple receive antennas is investigated over composite fading channel that takes the path loss, shadow fading and Rayleigh fading into account. Our aim is to maximize EE which is defined as the ratio of the transmission rate to the total consumed power under the constraints of maximum transmit power of each remote antenna. According to the definition of EE and using the upper bound of average EE, the optimized objective function is provided. Based on this, utilizing Karush-Kuhn-Tucker (KKT) conditions and mathematical derivation, a suboptimal energy efficient power allocation (PA) scheme is developed, and closed-form expression of PA coefficients is achieved. The developed scheme can obtain the EE close to the existing optimal scheme due to better approximation, especially for larger receive antenna number. Moreover, it has lower calculation complexity than the existing optimal scheme because only the statistic channel information is needed. Simulation results verify the effectiveness of the developed scheme.