# Crowded MTC Random Access in NOMA XL-MIMO

## TL;DR

This paper explores a novel NOMA-based random access protocol for crowded XL-MIMO systems, leveraging visibility regions to reduce access attempts and enhance data rates in high-density scenarios.

## Contribution

It introduces the NVR-XL protocol that exploits spatial non-stationarities and power domain NOMA to improve access efficiency in XL-MIMO systems.

## Key findings

- Reduces number of access attempts in crowded scenarios
- Improves average sum-rate with more sub-arrays
- Utilizes visibility regions for efficient user access

## Abstract

Massive MIMO is one of the key technologies to support the growth of massive access attempts by devices, such as in massive machine type communication (mMTC). The evolution of antenna array technology brought the recent extra-large scale massive multiple input multiple output (XL-MIMO) systems, seen as a promising technology for providing very high-data rates in high-user density scenarios. Spatial non stationarities and visibility regions (VRs) occur across all huge XL array extension, since its large dimension is of the same order of the distances to the user equipment (UE). We investigate the random access (RA) problem in crowded XL-MIMO scenarios. The proposed nonorthogonal multiple access (NOMA) visible region extra large array (NVR-XL) protocol takes advantage of the power domain NOMA to allow access of two or more users colliding in the same XL sub-array (SA) selecting the same pilot sequence. The NVRXL provides a reduction in the number of attempts to access the network, while improving the average sum-rate, as the number of SA increases.