  This paper considers the uplink of user-centric cell-free massive MIMO
(multiple-input multiple-output) systems. We utilize the user-centric dynamic
cooperation clustering (DCC) framework and derive the achievable spectral
efficiency with two-layer decoding that is divided between the access points
and the central processing unit (CPU). This decoding method is also known as
large-scale fading decoding (LSFD). The fronthaul signaling load is analyzed
and a nearly optimal second-layer decoding scheme at the CPU is proposed to
reduce the fronthaul requirements compared to the optimal scheme. We also
revisit the joint optimization of LSFD weights and uplink power control and
show that the corresponding max-min fair optimization problem can be solved
optimally via an efficient fixed-point algorithm. We provide simulations that
bring new insights into the cell-free massive MIMO implementation.
