  The multiple access channel (MAC) with many-user is a general model for
massive machine type communications. In this paradigm, the number of users may
be comparable or even larger than the coding blocklength $n$. In contrast,
classical MAC often assumes fixed and small number of the users. In this paper,
we consider the massive access channel with multiple antennas system, where the
base station (BS) with multiple receiving antennas serves the users in a single
cell. The magnitude of users is assumed to grow unbounded with $n$. We
investigate the achievable region of MIMO massive access channel, where among
the total users, an unknown subset referred to active users may transmit data
periodically. The asymptotic active user identification cost is also
quantified. With the theoretical analysis, it was shown that given finite
number of the receiving antennas, the individual rate for each user can be
formulated as the sum rate multiplied by some specific factors, which
correspond to the allocation of sum capacity. The successive decoding does not
apply due to the interferences from growing unbounded users. Theoretical
analysis shows that successive decoding works only when the number of receiving
antennas goes to infinity with the increasing codelength.
