# Rethinking Uplink Hybrid Processing: When is Pure Analog Processing Suggested?

## TL;DR

This paper analytically compares pure analog and hybrid processing in uplink massive MIMO systems, revealing conditions where analog processing can outperform hybrid schemes under certain assumptions.

## Contribution

It provides a theoretical analysis of achievable rates for pure analog and hybrid detection in uplink massive MIMO with sub-connected architecture, highlighting scenarios favoring analog processing.

## Key findings

- Analog processing can outperform hybrid processing under certain conditions.
- Derived expressions for achievable rates under Rayleigh fading.
- Performance varies with number of users and antennas.

## Abstract

In this correspondence, we analytically characterize the benefit of digital processing in uplink massive multiple-input multiple-output (MIMO) with sub-connected hybrid architecture. By assuming that the number of radio frequency (RF) chains is equal to that of users, we characterize achievable rates of both pure analog detection and hybrid detection under the i.i.d. Rayleigh fading channel model. From the derived expressions, we discover that the analog processing can outperform the hybrid processing using the maximal ratio combining (MRC) or zero-forcing (ZF) criterion in cases under some engineering assumptions. Performance comparison of the schemes are presented under tests with various numbers of users and numbers of antennas at the base station.