Precoding and Gain Adjustment Scheme for Block Low-Resolution DACs in Massive MIMO Downlink

In this paper, a nonlinear quantized precoding and gain adjustment scheme for low-resolution digital-analog converters (DACs) in a massive multiple-input multiple-output (MIMO) system is proposed. The nonlinear quantized precoding determines transmit antenna outputs with a transmit symbol and channel state information. In a full-digital massive MIMO system, low-resolution DACs are used to suppress power consumption. Conventional precoding algorithms for low-resolution DACs do not optimize transmit antenna gains individually. Thus, in this paper, a gain adjustment scheme that optimizes individual transmit antenna gains and the DAC outputs of a virtual block antenna formed by multiple antennas is proposed. Numerical results obtained through computer simulation show that the proposed precoding scheme achieves bit error rate performance close to that of the conventional Gibbs sampling based algorithm with much smaller antenna gains on a i.i.d Rayleigh fading channel.