  The recent extra-large scale massive multiple-input multiple-output (XL-MIMO)
systems are seen as a promising technology for providing very high data rates
in increased user-density scenarios. Spatial non-stationarities and visibility
regions (VRs) appear across the XL-MIMO array since its large dimension is of
the same order as the distances to the user-equipments (UEs). Due to the
increased density of UEs in typical applications of XL-MIMO systems and the
scarcity of pilots, the design of random access (RA) protocols and scheduling
algorithms become challenging. In this paper, we propose a joint RA and
scheduling protocol, namely non-overlapping VR XL- MIMO (NOVR-XL) RA protocol,
which takes advantage of the different VRs of the UEs for improving RA
performance, besides seeking UEs with non-overlapping VRs to be scheduled in
the same payload data pilot resource. Our results reveal that the proposed
scheme achieves significant gains in terms of sum rate compared with
traditional RA schemes, as well as reducing access latency and improving
connectivity performance as a whole.
