# Low Power Wide Area Network, Cognitive Radio and the Internet of Things: Potentials for Integration
## 5 Integrating Cognitive Radio in LPWAN for the Internet of Things
### CR-LPWAN at the PHY Layer  
Having motivated the need to develop and deploy CR-LPWAN technologies, a simplified concept of a PHY-layer front-end model of a CR-LPWAN system is presented. Recall that there are different available LPWAN technologies mentioned (see Section 3), which makes rendering an all-encompassing model a difficult task. Nevertheless, the model to be described is considered following ideas gleaned from three different well known platforms, including LoRa, Sigfox, and the Ingenu architectures. In this regard, such a simple CR-LPWAN PHY layer architecture is presented in Figure 3 wherein the surrounding spectrum is first scanned by the CR-LPWAN system in order to determine whether or not white spaces are available for use. To achieve this, the received signal is filtered to the required bandwidth of interest and fed to a low noise amplifier (LNA) to reduce noise samples. These signals are converted to their corresponding digital form and a fast Fourier transformation (FFT) operationis performed. The averaged signals are passed to the threshold estimator to determine a suitable threshold value for signal detection. Decision is made regarding the presence (\(H_{1}\)) or absence (\(H_{0}\)) of PU signals in the band. If the outcome is \(H_{0}\), then the spectrum access/sharing module is engaged, which formats the signal as required by the LPWAN module. However, if the outcome is \(H_{1}\), the spectrum mobility module is activated for expedite withdrawal from the band. This command is fed to the transmission controller, which disengages any on-going transmission process in the LPWAN module and simultaneously activates the switching module to begin sensing (receiving mode) rather than transmitting. However, if the \(H_{0}\) subsists, then the LPWAN module is activated for transmission. Some details pertaining to the individual blocks of this model are highlighted as follows [76]:  
1. **Antenna:** Antenna design plays an important role in improving the radio performance of CR-LPWAN systems. Effective antenna design can be vital in ensuring proper propagation characteristics and also in conserving energy consumption rates. Essentially, antenna wavelengths must be made to match the operating frequency of the device. The antenna form factor used also determines to a large extent the gain (or loss) of the system, in addition to the gain in the directivity of the antenna. Low cost antenna technologies were discussed in [77] with particular focus on cost efficient antennas for 868 MHz band. The antenna design in [77] comprised of an inverted F antenna (IFA) topology with simulation results of about -6 dB reflection coefficient in the 850-893 MHz band. A dipole radiation pattern was proposed. These are characteristics that should be considered in the antenna design of any CR-LPWAN system. [PERSON] et al., in [78] discussed the design of miniature antennas for IoT applications. Similar to [77], [PERSON]'s design [78] adopts the IFA topology. He noted that the overall IFA length is responsible for the lower antenna resonance relished in LoRa communication systems [78]. Essentially, proper consideration must be given to antenna design and structure for the efficient and effective deployment of CR-LPWAN systems. 2. **Switching Module:** The switching module is a Duplexer that enables bi-directional transmission over a single path. Its function is to separate the receiving path from the transmitting path while ensuring that a common antenna is shared. We suggest that CR-LPWAN models should deploy a switching module, whereas the choice of whether or not half or full duplex mode should be used, can be an application-specific decision. 3. **Low Noise Amplifier (LNA):** The LNA amplifies the received RF signal to increase the signal to noise ratio (SNR) at the CR-LPWAN receiver. We identity a few low-cost LNA modules that can be in CR-LPWAN systems. The duplex current reused CMOS LNA is a notable example with complementary derivative superposition technique that can be used in IoT devices [79].