# On the Performance of LDPC-Coded Massive MIMO Schemes with Power-Ordered NOMA Techniques
## 1 Introduction  
The Fourth Industrial Revolution consists of the revolution of robots. Artificial intelligence is utilized to support the decision-making of robots, namely, to process a large amount of data (big data) that is generated with high data rate communications and using a wide variety of sensors and Internet of Things (IoT) devices. The Fourth Industrial Revolution is already deeply modifying humans and society in a myriad of areas, such as economy, mobility, housing, teaching, health, agriculture, medical and lawyer counselling, defense, wildlife monitoring, etc. [1, 2]. From the communication and IoT point of view, the fifth generation of cellular communications (5G) was designed to offer the services required by the Fourth Industrial Revolution, representing a modification of the paradigm when compared to previous generations. One novelty of 5G relies on the ability to support direct device-to-device communication without requiring a base station, which is needed to support IoT devices required for autonomous vehicles, smart logistics, and smart cities. Moreover, as can be seen from Figure 1, to support different services with the required reliability, 5G is split into three groups of use cases: Enhanced Mobile Broadband (eMBB), massive Machine-Type Communications (mMTC) and Ultra-Reliable Low Latency Communications (URLLC). These three groups support the network slicing concept, which aims to provide diverse requirements for different users. For example, smart cities employ an extremely high number of devices with low power consumption, which is supported by mMTC. On the other side, autonomous vehicles require communication that is highly reliable and almost real-time, which is supported by URLLC. Standardized in 2018 by the Third Generation Partnership Project (3 GPP) Release 15, the initial phase of 5G focused on the improvement of broadband wireless cellular services (eMBB). The other two groups of use cases (mMTC and URLLC) have been defined in the 3 GPP release 16 in 2020 to also include the new air interface known as 5G New Radio (NR) and the network slicing concept. Release 17 is expected in 2022, and it will focus on several improvements to 5G, such as network slicing, URLLC, and improved capacity/spectral efficiency, as will be required to support billions of IoT devices needed for smart logistics, smart cities, and autonomous vehicles. Non-Orthogonal Multiple Access (NOMA) is a potential candidate to reach such improved spectral efficiency [3]. In 2005, Quasi-Cyclic Low-Density Parity-Check (QC-LDPC) encoding [4], which is based on the cyclic change of the identity matrix and is also referred to as \"structured\" LDPC encoding [5], was applied for the first time in the World Interoperability for Microwave Access (WiMAX) standard. The QC-LDPC codes can be defined by a survey size and a base matrix. In 2006, QC-LDPC codes were also recommended for long-term evolution (LTE) channel coding [6]. Later, QC-LDPC codes with the same structure as WiMAX were adopted by IEEE802.11n and IEEE802.11 ad because of their remarkable performance and high decoding throughput. In October 2016, QC-LDPC codes were adopted by 3 GPP as a data channel encoding scheme for 5G standard because they support very high data transfer rates with low complexity, as opposed to turbo codes utilized in 3G and 4G [7]. Previous work on NOMA focuses mainly on its association with Orthogonal Frequency Division Multiplexing (OFDM) [3; 8; 9; 10; 11]. Moreover, the study published in [12] focused on the combination of NOMA with massive Multiple-Input Multiple-Output (MIMO), using the Single Carrier with Frequency Domain Equalization (SC-FDE) block transmission technique. This article publishes a holistic study where conventional NOMA and cooperative NOMA are combined with the Low-Density Parity-Check (LDPC) coded massive MIMO (m-MIMO) scheme, SC-FDE and multiple receivers with different levels of complexity and performance, and then studied in different 5G scenarios.