## 2 Spectrum Management and Graph Signal Processing  
In the literature, there are different spectrum management techniques. For example, the Non-Orthogonal Multiple-Access (NOMA) technique for CR was selected for radio access in 5G mobile wireless networks, as explained in [26; 27; 28]. In addition, the Rate  
Figure 1: Cognitive radio capability characteristics. Splitting Multiple-Access (RSMA) technique is a multiple-access technique that combines both the space-division multiple-access (SDMA) technique and the NOMA technique, as explained in [29]. The proposal uses the DSA technique, which is an essential tool in CR technology, so that it provides the CR technology with the capability to choose the most suitable free frequency bands in which the SU subscribers can work and operate at a given location over a certain available time. Thus, the DSA technique has main two keys, which are the co-access process power incentives and the co-access region area. The power donation process from the SU system to the PU system, which is called incentive, ensures that both the PU subscribers and the CR subscribers are in a win-to-win situation during system operation. Moreover, the coverage area, which is called the region of co-access, can be defined as the region area where the SU subscribers can access the frequency spectrum with the PU subscribers. The DSA models in [30] are classified into three types which are called (a) interweave, (b) underlay, and (c) overlay, as shown in Figure 2.  
Firstly, in the case of the interweave model, the CR node can start the transmission only if the PU slot is free and not occupied by the PU subscriber. So, the PU subscriber has strong legal rights on its own frequency spectrum. Hence, if the PU subscriber starts the transmission on his legal frequency band, then the CR is forced to be inactive on the legal band and look to another free PU band. Therefore, the interweave model in many studies is assigned to be the default model for the DSA management technique and is termed the opportunistic spectrum access (OSA) technique [9]. Thus, in the case of interweave, the CR subscribers are encouraged under strong conditions to utilize the spectrum free bands or holes, called white spaces, in the temporal domain, spatial domain, and frequency domain. Secondly, the underlay and the overlay management models, as shown in Figure 2, allow the CR subscribers to run the power transmission on the legal frequency spectrum regardless of whether the legal PU subscriber is accessing the frequency band or not. In addition, in the case of the underlay and overlay models, the transmission permission is still constrained to the condition where the total affected interference from all the SU subscribers is accepted and expected by the legal PU subscribers [30]. In the literature, several researchers discussed the different DSA management techniques that allow the CR subscribers to use and access the PU subscribers spectrum simultaneously without decreasing the PU subscriber capacity or decreasing the QoS level [9; 15; 31; 32]. Two cases are explained below for comparison with our proposal:  
Figure 2: The classification of the DSA management models. (a) Interweave model (b) Underlay Model (c) Overlay Model  
A management dynamic spectrum co-access (DSCA) technique was proposed in [10]. This technique enables the CR subscriber to access the legal frequency spectrum of the privileged PU by increasing the SNR of the privileged PU subscriber. In [10], the CR system donates a ratio of its transmission power to the privileged PU system as a power incentive that enables the CR system to co-access the legal frequency spectrum. Thus, in [10], the DSCA technique understands that the CR system recognizes the message of the PU system, and the CR system in this case uses a dirty paper coding (DPC) technique that requires a certain type of design complexity to avoid interfering with the transmitted data of the PU system.