  We consider the downlink of a cell-free massive multiple-input
multiple-output (MIMO) system with \textcolor{red}{single}-antenna access
points (APs) and single-antenna users. An iterative robust minimum mean-square
error (RMMSE) precoder based on generalized loading is developed to mitigate
interference in the presence of imperfect channel state information (CSI). An
achievable rate analysis is carried out and optimal and uniform power
allocation schemes are developed based on the signal-to-interference-plus-noise
ratio. An analysis of the computational costs of the proposed RMMSE and
existing schemes is also presented. Numerical results show the improvement
provided by the proposed RMMSE precoder against linear minimum mean-square
error, zero-forcing and conjugate beamforming precoders in the presence of
imperfect CSI.
