  In this work, a scalable and modular architecture for massive MIMO base
stations with distributed processing is proposed. New antennas can readily be
added by adding a new node as each node handles all the additional involved
processing. The architecture supports conjugate beamforming, zero-forcing, and
MMSE, where for the two latter cases a central matrix inversion is required.
The impact of the time required for this matrix inversion is carefully analyzed
along with a generic frame format. As part of the contribution, careful
computational, memory, and communication analyses are presented. It is shown
that all computations can be mapped to a single computational structure and
that a processing node consisting of a single such processing element can
handle a broad range of bandwidths and number of terminals.
