Multiuser Equalizer for Hybrid Massive MIMO mmWave CE-OFDM Systems

Roberto Magueta,Rui Dinis,Adão Silva,Atílio Gameiro,Daniel Castanheira,Sara Teodoro

doi:10.3390/app9163363

Abstract

This paper considers a multiuser broadband uplink massive multiple input multiple output (MIMO) millimeter-wave (mmWave) system. The constant envelope orthogonal frequency division multiplexing (CE-OFDM) is adopted as a modulation technique to allow an efficient power amplification, fundamental for mmWave based systems. Furthermore, a hybrid architecture is considered at the user terminals (UTs) and base station (BS) to reduce the high cost and power consumption required by a full-digital architecture, which has a radio frequency (RF) chain per antenna. Both the design of the UT’s precoder and base station equalizer are considered in this work. With the aim of maximizing the beamforming gain between each UT and the BS, the precoder analog coefficients are computed as a function of the average angles of departure (AoD), which are assumed to be known at the UTs. At the BS, the analog part is derived by assuming a system with no multi-user interference. Then, a per carrier basis nonlinear/iterative multi-user equalizer, based on the iterative block decision feedback equalization (IB-DFE) principle is designed, to explicitly remove both the multi-user and residual inter carrier interferences, not tackled in the analog part. The equalizer design metric is the sum of the mean square error (MSE) of all subcarriers, whose minimization is shown to be equivalent to the minimization of a weighted error between the hybrid and the full digital equalizer matrices. The results show that the proposed hybrid multi-user equalizer has a performance close to the fully digital counterpart.

Highlights

IntroductionMost communication systems use a frequency spectrum in the 300 MHz–3 GHz band [1]
Most communication systems use a frequency spectrum in the 300 MHz–3 GHz band [1]. This has led to a high level of congestion in this frequency band and the inability to respond to increased demands on new communication systems, in terms of new services and data rates
Since the analog part is computed in the first iteration, for simplicity, we removed the index i, and MSEk corresponds to MSEk

Summary

Introduction

Most communication systems use a frequency spectrum in the 300 MHz–3 GHz band [1]. This has led to a high level of congestion in this frequency band and the inability to respond to increased demands on new communication systems, in terms of new services and data rates. Sci. 2019, 9, 3363 due to the small wavelengths inherent to these bands, we can pack these hundreds of antennas in the same volume of sub-6 GHz systems [4]. There are three major architectures that can be explored. The first one, it is the use of low-resolution DACs/ADCs

Objectives

Methods

Results

Conclusion