  We consider an extension of the massive unsourced random access originally
proposed by Polyanskiy to the case where the receiver has a very large number
of antennas (a massive MIMO base station) and no channel state information is
given to the receiver (fully non-coherent detection). Our coding approach
borrows the concatenated coding idea from Amalladinne et. al., combined with a
novel non-Bayesian `activity detection' algorithm for massive MIMO random
access channels, that outperforms currently proposed Bayesian vector AMP (VAMP)
schemes currently proposed for activity detection, and does not suffer from the
numerical instabilities and requirement for accurate a priori statistics as
VAMP. We show that the required transmit $E_b/N_0$ for reliable communication
can be made arbitrarily small as the number of receiver antennas M grows
sufficiently large.
