Energy-efficient multicast resource allocation based on beamforming technique

This paper proposes an energy-efficient multicast scheme for downlink orthogonal frequency division multiplexing (OFDM) system in which the base station (BS) is equipped with multiple antennas. We employ the multiple description coding multicast (MDCM) model and beamforming technique to maximize the energy efficiency (EE) with the constraint on total transmit power. In MDCM, the transmission rate is not limited by the user with the minimum channel quality any more. And the beamforming technique can enhance the signal strength of the weakest user. In this paper, a two-step suboptimal scheme is studied. Firstly, the beamforming weighted vector (BWV) is obtained by a vector splitting algorithm, and then the power and subcarrier allocation is realized by fractional programming and subgradient method. Numerical results reveal that the proposed scheme can achieve near optimal EE and greatly improve the EE compared with two spectrum-efficient schemes. In addition, the energy-efficient scheme can render a good performance in EE as well as throughput when the total transmit power is small.