# Cooperative SWIPT MIMO-NOMA for Reliable THz 6G Communications
## 2 Background  
To develop a communication system that meets the extreme values of the emerging requirements in terms of connectivity, SE, latency, data rate, reliability, and user fairness, enabling new applications, EE, and cost-effectiveness, it is necessary to merge some of the key enabling techniques to achieve the required objectives. As a result, nonorthogonal multiple access in the power domain (NOMA) [19] is the most well-known nominee for developing 6G systems, exceeding the performance of traditional orthogonal multiple access (OMA) schemes. Multiple-input multiple-output (MIMO)-NOMA is the focus of our study. The NOMA mechanism superimposes multiple signals at the transmitter (Tx), and then filters them at the receiver (Rx) by successive interference cancelation (SIC) procedures, thereby increasing channel capacity primarily determined by BW. The interference and noise, on the other hand, are removed by the SIC at the Rx. NOMA multiplexing is achieved by allocating different power coefficients to users on the basis of their channel conditions. At Tx, all users' signals are overlaid. The application of SIC at Rx is used to demultiplex NOMA signals. Because the line of sight (LoS) is the primary transmission path, grouping or clustering of the serviced users is critical for improving SE and reducing the complexity of NOMA-based THz transmission. MIMO-based NOMA BS/users depend basically on channel state information (CSI) (or other metrics often) for successful SIC decoding at the Rx. With a large number of users, user clustering may be difficult; consequently, we strive to design low-complexed systems to solve clustering complications [20, 21]. Hence, not only is SIC operation CSI-related, but it can also be quality service-related or hybrid-related [20]. However, all modulation systems have a significant barrier to CSI acquisition at the Tx and Rx [14]. As a result, we employ binary phase-shift keying (BPSK) in the proposed system, which has several advantages over other formats. To address the challenges of THz communications, researchers are looking into all options, highlighting NOMA-assisted cooperative networks. Cooperative networking provides a number of benefits, including increased reliability and capacity, as well as a larger coverage area, all of which improve overall performance, i.e., implementing energy harvesting (EH) with cooperative NOMA [22], which is the focus of the proposed article of THz communications. While applying NOMA to the proposed system, decode-forward (DF) relaying is adopted instead of the complex and costly intelligent reflecting surface (IRS). In NOMA, the far users' signal is already contained in the superposed signal; therefore, that copy can be utilized for relaying. That is preferable to utilizing an additional relaying device with additional complexity and power consumption. While THz-NOMA requires heavy computational SIC operations at the Rx, employing cooperative networking continually drains the relaying user's battery, resulting in system failure. As a result, research activities are aimed at overcoming that issue, transforming into green communications [23] by applying the EH technique. Radiofrequency (RF) power, which exists everywhere surrounding almost all user equipment (UE), is used to send energy and information to distant destinations. Using basic RF circuits, EH allows UEs to harvest that energy. We can then use that gathered power in the broadcasts to convey signals without putting additional strain on the relaying user's battery. Through EH power splitting, the relaying user splits the power it receives into harvesting and decoding fractions, operating them at the same time, resulting in the principle of simultaneous wireless information and power transfer (SWIPT). SWIPT enables the relaying user to capture power from the transmitted signal and use it for data retransmission to a farther user, as depicted in Figure 1. Ultimately, the entire capacity and outage probability (OP) are significantly improved.