# On Performance of Quantized Transceiver in Multiuser Massive MIMO Downlinks

## TL;DR

This paper analyzes the impact of low-resolution DACs and ADCs on the downlink performance of multiuser massive MIMO systems, deriving asymptotic achievable rates and quantifying rate loss due to quantization at different SNR levels.

## Contribution

It provides a theoretical framework using Bussgang theorem to quantify the rate loss caused by finite-bit converters in massive MIMO downlinks, revealing conditions for maintaining performance.

## Key findings

- Quantization distortion is negligible at low SNR with low-resolution converters.
- One additional bit of DAC resolution is needed at high SNR when user load increases.
- The required DAC resolution can be approximated by a formula involving ADC resolution and user load.

## Abstract

Low-resolution digital-to-analog converters (DACs) and analog-to-digital converters (ADCs) are considered to reduce cost and power consumption in multiuser massive multiple-input multiple-output (MIMO). Using the Bussgang theorem, we derive the asymptotic downlink achievable rate w.r.t the resolutions of both DACs and ADCs, i.e., $b_{DA}$ and $b_{AD}$, under the assumption of large antenna number, $N$, and fixed user load ratio, $\beta$. We characterize the rate loss caused by finite-bit-resolution converters and reveal that the quantization distortion is ignorable at low signal-to-noise ratio (SNR) even with low-resolution converters at both sides. While for maintaining the same rate loss at high SNR, it is discovered that one-more-bit DAC resolution is needed when more users are scheduled with $\beta$ increased by four times. More specifically for one-bit rate loss requirement, $b_{DA}$ can be set by $\left\lceil b_{AD}+\frac{1}{2}\log\beta \right\rceil$ given $b_{AD}$. Similar observations on ADCs are also obtained with numerical verifications.