## 2 Materials and Methods
### How Cognitive Radio Engage with the Industrial IoT?
#### 2.1.5 Spectrum Allocation  
The radio frequency spectrum allocation to unlicensed users depends on the central spectrum in cognitive IIoT-based LPWAN. Although a centralized sensing technique is available for collecting information on free frequencies, sometimes decentralized sending technique also plays a part. The spectrum availability is scanned by the transceiver on the IIoT device and sent by access points using a specified network. This spectrum access process allows allocating a specific spectrum channel to a certain cognitive user on the IIoT device based on availability [74]. In spectrum access, the radio technique for unlicensed frequency users to effectively access the unutilized licensed bands to decrease the new frequency bands or white area is recognized as the dynamic access frequency band. Figure 7: Radiofrequency network architecture [72; 73]. In this platform, frequency band unlicensed users essentially use unused licensed frequency bands without damage. When the frequency licensed band of the user initiates the frequency band, the frequency band unlicensed user has to create the free frequency band and transmit it to another inactive radio. The Cognitive Radio techniques and frequency spectrum dynamic access platform significantly improve resolution for upgrading frequency utilization in the cognitive radio [75]. Dynamic access is a technique wherein the frequency spectrum holes in spectrum radio allocation mean the radio spectrum is used proactively. Fixed allocation sources based totally on the static spectrum get right of entry to be unsuitable for cooperating with spectrum radio disabilities anticipated to proportion sources. On the contrary, dynamic resource allocation functions well using spectrum holes or spectrum accessible bandwidth, by applying several approaches. Various shared radio resources have distinctive structures and can allocate several constant frequency bandwidths to numerous structures. The media access control (MAC) or channel allocation in LPWANs are better to explain so that the percentage of resources can turn out to be dependent on special SINR within the wireless software; the LPWANs can contribute to the Wi-Fi applications with difficult QoS demands [76]. The planner ought to decide a mac protocol of CR based on IIoT, based totally on numerous vital requirements. Firstly, IIoT devices are unique in using massive data, higher cost, communique vicinity, electricity consumption, and communication devices. Secondly, the checked radio frequency band is widespread. Many essential operators play approximately the function of choosing a mac protocol for the IIoT machine. The operators are communication probability, delays, and power consumption. Therefore, purposeful MAC protocol has to tolerate decrease fees, decrease complexity, and low strength intake. A mac protocol has to be as much as the correct errors. For example, this work [77] offers a comprehensive evaluation among mac types of standards, IEEE 802. 11 ah, and IEEE 802.15.4. The requirements are consistent with its structures. The IEEE 802.15.4 is a better deployable system than the IEEE 802.11 ah or IEEE 802.14 because of its energy saving and networkability permits regulating a huge number of IIoT devices system in unlicensed 2.4 using Direct Sequence Spread Spectrum (DSSS). Numerous smart devices allow MAC protocols, for instance, slotted aloha and acquainted Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA); and orthogonal frequency division multiple Access (OFDMA) and Frequency Hopping Spread Spectrum (FHSS) were deployed for IIoT LPWAN systems for applying the spectrum [78]. For instance, a CSMA/CA MAC protocol [79]. Cognitive LPWAN is an especially designed dynamic radio where the primary radio network (pm) structures with a huge number of radio sources become underutilized; so the cognitive radio LPWANs, the green get admission to is primary to the dynamic spectrum control for being closely deployed within the IoT [80].