# Multi-Cell Sparse Activity Detection for Massive Random Access: Massive MIMO versus Cooperative MIMO

## TL;DR

This paper compares massive MIMO and cooperative MIMO architectures for sparse device activity detection in cellular machine-type communications, analyzing their effectiveness in reducing interference and improving detection accuracy.

## Contribution

It provides an analytical comparison of massive MIMO and cooperative MIMO for activity detection, including the impact of fronthaul quantization and practical performance insights.

## Key findings

- Massive MIMO reduces detection errors as antennas increase.
- Cooperative MIMO improves cell-edge user detection.
- Cooperation with fewer antennas can match massive MIMO performance.

## Abstract

This paper considers sparse device activity detection for cellular machine-type communications with non-orthogonal signatures using the approximate message passing algorithm. This paper compares two network architectures, massive multiple-input multiple-output (MIMO) and cooperative MIMO, in terms of their effectiveness in overcoming inter-cell interference. In the massive MIMO architecture, each base station (BS) detects only the users from its own cell while treating inter-cell interference as noise. In the cooperative MIMO architecture, each BS detects the users from neighboring cells as well; the detection results are then forwarded in the form of log-likelihood ratio (LLR) to a central unit where final decisions are made. This paper analytically characterizes the probabilities of false alarm and missed detection for both architectures. Numerical results validate the analytic characterization and show that as the number of antennas increases, a massive MIMO system effectively drives the detection error to zero, while as the cooperation size increases, the cooperative MIMO architecture mainly improves the cell-edge user performance. Moreover, this paper studies the effect of LLR quantization to account for the finite-capacity fronthaul. Numerical simulations of a practical scenario suggest that in that specific case cooperating three BSs in a cooperative MIMO system achieves about the same cell-edge detection reliability as a non-cooperative massive MIMO system with four times the number of antennas per BS.