EMA: Energy-Efficiency-Aware Multiple Access

To improve the energy efficiency (EE) of an orthogonal frequency-division multiple access system with multiple transmit antennas supporting multiple single-receive-antenna users, we propose an EE-aware multiple access (EMA) scheme. The EMA selects an energy-efficient channel access method that is either time-division multiple access (TDMA) or space-division multiple access (SDMA) for each subband. For the SDMA, the near optimal number of SDMA time slots is derived. Numerical results verify that the EE of pure TDMA and SDMA can be significantly improved through the proposed EMA scheme.