  In this letter, we consider the uplink of a cell-free Massive multiple-input
multiple-output (MIMO) network where each user is decoded by a subset of access
points (APs). An additional step is introduced in the cell-free Massive MIMO
processing: each AP in the uplink locally implements soft MIMO detection and
then shares the resulting bit log-likelihoods on the front-haul link. The
decoding of the data is performed at the central processing unit (CPU),
collecting the data from the APs. The non-linear processing at the APs consists
of the approximate computation of the posterior density for each received data
bit, exploiting only local channel state information. The proposed method
offers good performance in terms of frame-error-rate and considerably lower
complexity than the optimal maximum-likelihood demodulator.
