  To keep massive MIMO systems cost-efficient, power amplifiers with rather
small output dynamic ranges are employed. They may distort the transmit signal
and degrade the performance. This paper proposes a distortion aware precoding
scheme for realistic scenarios in which RF chains have nonlinear
characteristics. The proposed scheme utilizes the method of regularized
least-squares (RLS) to jointly compensate the channel impacts and the
distortion imposed by the RF chains.
  To construct the designed transmit waveform with low computational
complexity, an iterative algorithm based on approximate message passing is
developed. This algorithm is shown to track the achievable average signal
distortion of the proposed scheme tightly, even for practical system
dimensions. The results demonstrate considerable enhancement compared to the
state of the art.
