# Massive MIMO Techniques for 5G and Beyond—Opportunities and Challenges

^{1}

^{2}

^{3}

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## Abstract

**:**

## 1. Introduction

#### Notation

## 2. MIMO Techniques

#### 2.1. Channel Capacity

#### 2.1.1. SISO

#### 2.1.2. SIMO

#### 2.1.3. MISO

#### 2.1.4. MIMO

#### 2.2. Signal Modulation

## 3. Massive MIMO

- Huge spectral efficiency;
- Communication reliability;
- High energy efficiency;
- Low complexity signal processing;
- Favorable propagation;
- Channel hardening.

## 4. Implementation Difficulties

## 5. MIMO Implementations

**F**

^{ZF}is calculated directly from the propagation channel $\mathbf{H}$ as follows:

#### Multi-Layer Massive MIMO

## 6. Promising Solutions

## 7. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## Abbreviations

ADC | Analog-to-Digital Converter |

AOA | Angle Of Arrival |

AOD | Angle Of Departure |

BPSK | Binary Phase Shift Keying |

BS | Base Station |

CDMA | Code Division Multiple Access |

CP | Cyclic Prefix |

DAC | Digital-to-Analog Converter |

DFE | Decision Feedback Equalizer |

DL | Downlink |

EGC | Equal Gain Combiner |

EGT | Equal Gain Transmitter |

FDE | Frequency Domain Equalization |

FFT | Fast Fourrier Transform |

IB-DFE | Iterative Block Decision Feedback Equalizer |

ICI | Inter Carrier Interference |

IFFT | Inverse Fast Fourier Transform |

IOT | Internet of Things |

ISI | Inter Symbol Interference |

LoS | Line-of-Sight |

M2M | Machine to Machine |

MC | Multi-Carrier |

MIMO | Multiple-Input Multiple-Output |

MISO | Multiple-Input Single-Output |

MMSE | Minimum Mean Squared Error |

mmWave | Millimiter Wave |

MRC | Maximum Ratio Combiner |

MRT | Maximum Ratio Transmitter |

MU-MIMO | Multi-User Multiple-Input Multiple-Output |

NL | NonLinear |

NLoS | Non-Line-of-Sight |

OFDM | Orthogonal Frequency Division Multiplexing |

PAPR | Power to Average Power Ratio |

PSK | Phase Shift Keying |

QAM | Quadrature Amplitude Modulation |

QoS | Quality of Service |

QPSK | Quaternary Phase Shift Keying |

RF | Radio Frequency |

SC | Single Carrier |

SDMA | Space Division Multiple Access |

SIMO | Single-Input Multiple-Output |

SISO | Single-Input Single-Output |

SNR | Signal to Noise Ratio |

STBC | Space Time Block Code |

SVD | Singular Value Decomposition |

TDD | Time-Division Duplexing |

UE | User Equipment |

UL | Uplink |

ZF | Zero Forcing |

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**MDPI and ACS Style**

Borges, D.; Montezuma, P.; Dinis, R.; Beko, M.
Massive MIMO Techniques for 5G and Beyond—Opportunities and Challenges. *Electronics* **2021**, *10*, 1667.
https://doi.org/10.3390/electronics10141667

**AMA Style**

Borges D, Montezuma P, Dinis R, Beko M.
Massive MIMO Techniques for 5G and Beyond—Opportunities and Challenges. *Electronics*. 2021; 10(14):1667.
https://doi.org/10.3390/electronics10141667

**Chicago/Turabian Style**

Borges, David, Paulo Montezuma, Rui Dinis, and Marko Beko.
2021. "Massive MIMO Techniques for 5G and Beyond—Opportunities and Challenges" *Electronics* 10, no. 14: 1667.
https://doi.org/10.3390/electronics10141667