## 2 Materials and Methods
### How Cognitive Radio Engage with the Industrial IoT?
#### 2.1.3 Cognitive Industrial Internet of Things (IIoT)  
The growth of IIoT applications in different aspects will require enabling protocols and more spectrum due to different kinds of devices, sensors, and things that can be connected to the Internet. Available spectrum will become rare relative to this phenomenal growth, especially in the Industrial, Scientific, and Medical Bands. Technologies such as LoWPAN and ZigBee depend on ISM bands that are not sufficient for their needs for a spectrum [59]. Cognitive radio in IIoT with dynamic spectrum access can be more aggressive, in which multiple users can simultaneously use a channel if only it satisfies the predefined quality condition. The use of cognitive technology in IIoT will help to bring control to IIoT growth issues in the case of channels distribution among devices shared with infrastructure-based development through radio connections [60]. The operational planning for Cognitive IIoT fundamentally characterizes the interactivities of mainly five essential cognitive functions: intelligence cycle, large data test, logic knowledge, derivation, and detection. Intelligent systems decide for resolution and request services supplying similar signals useful for the IIoT model [61; 62]. Cognitive processing in IIoT network based on cellular backbone architecture as shown in Figure 6 enables IIoT devices to determine its action [63]. This can be accomplished by exchanging local event information between the sensor nodes and servers. Besides, IIoT devices can exchange control data for spectrum allocation and channel determination for handover. The radio sensing integration with cloud-enabled services can assist as self-reconfigurable IIoT resolutions for an implementation application [64]. Another cognitive IIoT consideration is the use of coexistence performance of hot spot indoor with LTE [65]. The coexistence system of ZigBee and LTE will promise more performance explored through the different communication networks since LTE offers low density in rural regions and ZigBee high density for urban regions. The integration between LTE and ZigBee configuration will introduce a new approach to different spectrum bands in one architecture without the spectrum sharing aspect [66]. In cognitive IIoT in LTE access technology, the spectrum sensing is a process that enables Secondary Users (SUs) to sense the spectrum with a given probability to detect and protect the signal from Primary Users (PUs) possibly in noisy environments [67]. It should be that the PUs signal must be identified for SUs communication at the desired interference level. For perfect sensing performance, two metrics, the probability of misdetection and false alarm, should be considered in cognitive IIoT system evaluation [64]. False alarm represents that \(SU\) discovers that the idle PU is active, which can miss transmission opportunity. The following equation determines the probability of false alarm [68]:  
\[P_{fa}=C\bigg{(}\bigg{(}\frac{\lambda}{v^{2}}-1\bigg{)}\sqrt{T\cdot F_{S}} \bigg{)}, \tag{1}\]  
where \(C\) represents the complementary distribution function of a standard Gaussian, \(\lambda\) denotes the spectrum sensing threshold, \(v^{2}\) is the channel power noise, \(T\) denotes the spectrum sensing time, and \(f\)s indicates the sampling rate of the channel. The detection probability of an arbitrary \(SU\)\(i\) is derived as follows [69]:  
\[P_{su}=C\bigg{(}\bigg{(}\frac{1}{\sqrt{2\gamma+1}}-1\bigg{)}C^{-1}\Big{(}P_{fa }\Big{)}-\sqrt{T\cdot F_{S}}\gamma\bigg{)}, \tag{2}\]  
where \(\gamma\) represents the SINR of the PU's signal measured at the \(SU\). The misdetection probability for \(SU\) can be written by:  
\[P_{md}=1-P_{su}. \tag{3}\]  
Cognitive radio performance can affect the sensing ability during the detection process of the active SUs. Multipath fading problems in wireless channels that appeared in PUs will make SUs fail in the process of PUs detection, which will push the SUs to cause much interference to the PUs in their successive transmissions [70].