###### Abstract  
In this paper, we propose an underlay cognitive radio (CR) system that includes subscribers, termed secondary users (SUs), which are designed to coexist with the spectrum owners, termed primary users (PUs). The suggested network includes the PUs system and the SUs system. The coexistence between them is achieved by using a novel dynamic spectrum co-access multicarrier-based cognitive radio (DSCA-MC-CR) technique. The proposal uses a quadrature phase shift keying (QPSK) modulation technique within the orthogonal frequency-division multiplexing (OFDM) scheme that maximizes the system data rate and prevents data inter-symbol interference (ISI). The proposed CR transmitter station (TX) and the CR receiver node (RX) can use an advanced smart antenna system, i.e., a multiple-input and multiple-output (MIMO) system that provides high immunity against channel impairments and provides a high data rate through its different combining techniques. The proposed CR system is applicable to coexist within different existing communication applications like fifth-generation (5G) applications, emergence applications like the Internet of Things (IoT), narrow-band (NB) applications, and wide-band (WB) applications. The coexistence between the PUs system and the SUs system is based on using power donation from the SUs system to improve the quality of the PU signal-to-interference-and-noise ratios (SINRs). The green communication concept achieved in this proposal is compared with similar DSCA proposals from the literature. The simulations of the proposed technique show enhancement in the PUs system throughput and data rate along with the better performance of the SUs system. dynamic spectrum co-access; cognitive radio; OMNeT++; graph signal processing; MIMO systems; packet interarrival analysis +
Footnote †: journal: Applied sciences  
This paper presents a contribution towards achieving an efficient usage of the frequency spectrum by enabling CR industrial technology through a newly proposed technique called the dynamic spectrum co-access multicarrier-based cognitive radio (DSCAC-MC-CR) technique. In addition, the proposed network aims to increase the communication system capacity, achieve an ultra-high data rate and ultra-low latency, and constitute an efficient, reliable, and secure green communication system. Thus, spectrum co-access exists between the privileged PUs system that already has legal rights over a certain band of the spectrum and the SUs system that represents the CR that desires access to the PU legal spectrum without any interference with the PU communication system. Also, the suggested proposal operates the CR system simultaneously with the privileged primary system by presenting donation power from the SU system to the PU system, without any change in the infrastructure of the privileged PU system. Furthermore, the proposed work aims to increase the primary system coverage area, capacity, and system throughput. At the same time, the SU system should achieve excellent performance and proper quality of service (QoS) by using advanced signal processing techniques within the transmission and reception process of the CR system. The suggested proposal employs the dynamic spectrum access (DSA) technique to manage the spectrum, providing an excellent tool with which regulators can efficiently manage and improve the utilization of the spectrum [11; 12; 13; 14; 15; 16; 17]. In addition, to guarantee SU communication system stability, it allows the SU transmitter to act as a relay node within the proposed network to help the PU transmission data. In order to achieve this, the CR transmitter node is allowed to access the PU-RF spectrum and transmit its RF data in different models. The MIMO smart antenna system can be employed to improve the system's performance. The MIMO antenna system works efficiently in the complicated propagation channels and achieves improvement in system performance due to the transmission and reception antenna diversity [18; 19; 20].