  The use of massive multiple-input multiple-output (MIMO) to serve a crowd of
user equipments (UEs) is challenged by the deficit of pilots. Assuming that the
UEs are intermittently active, this problem can be addressed by a shared access
to the pilots and a suitable random access (RA) protocol. The strongest-user
collision resolution (SUCRe) is a previously proposed RA protocol that often
privileges the UEs closer to the base station (BS). In contrast, we propose a
novel RA protocol using a decentralized pilot power allocation method that aims
at a fairer performance. The proposed access class barring with power control
(ACBPC) protocol allows each UE to estimate, without additional overhead, how
many UEs collided for the chosen pilot and calculate an ACB factor, which is
then used to determine the pilot retransmission probability in the next
protocol step. The results show that the proposed ACBPC protocol is superior to
SUCRe in terms of providing a fair connectivity for very crowded networks,
although still being distributed and uncoordinated as the original SUCRe
protocol.
