Quantized Polar Transmitters for Power Efficient Massive MIMO Systems

Guixian Xu,Jussi Ryynanen,Marko Kosunen,Vesa Lampu,Lauri Anttila,Mikko Valkama,Kari Stadius

doi:10.1109/lwc.2020.3046952

Abstract

This letter investigates the feasibility of the quantized digital polar transmitter architecture in a downlink multi-user massive multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) system, where a low amplitude resolution and a moderate phase resolution are utilized. We derive a lower bound on the average sum-rate achievable with Gaussian signaling inputs and linear precoding by a simple diagonal approximation for the quantization distortion. The analysis and simulations demonstrate that the quantized polar transmitter can enable excellent performance in terms of average sum-rate throughput, symbol error rate (SER), and out-of-band (OOB) emission level, thus providing an attractive option for the traditional Cartesian architecture.

Highlights

T HE PRACTICAL implementation of a massive multipleinput multiple-output (MIMO) transmitter with hundreds or even thousands of antennas is a significant challenge for the future generation of cellular networks [1]
To conquer the power efficiency challenge, a well-known option is to use constant envelope (CE) waveforms, which would enable the utilization of power-efficient switching power amplifiers (PAs)
MIMO system with orthogonal frequencydivision multiplexing (OFDM) transmission over frequencyselective channels, where the base station (BS) is equipped with Nt antennas, simultaneously serving K single-antenna user equipments (UEs)

Summary

INTRODUCTION

T HE PRACTICAL implementation of a massive multipleinput multiple-output (MIMO) transmitter with hundreds or even thousands of antennas is a significant challenge for the future generation of cellular networks [1]. The constant amplitude antenna signals are generated, through optimization, from original single-carrier I/Q signals with larger PAPR, and the I/Q modulated signals are reconstructed at the receiver antennas This approach, suffers from a loss in the achievable data rate, since. Though sub-optimal, alternative is to use linear precoding together with low-resolution digital-toanalog converters (DACs), as was proposed and analyzed in [5] in the context of the Cartesian transmitter architecture. In this structure, a digital phase modulator is feeding a poweramplifying RF-DAC unit, being digitally controlled with the quantized amplitude signal [7]. Simulation results demonstrate the superior performance of the polar architecture in terms of average sum-rate, symbol error rate (SER), and out-of-band (OOB) emission level, compared to the Cartesian architecture

SYSTEM MODEL

Polar Transmitter Architecture

Uniform Quantization

Achievable Sum-Rate With Gaussian Signaling

The Computation of Cd

Diagonal Approximation

SIMULATION RESULTS AND CONCLUSION