## 3 Development of Thermal Condition Monitoring System
### Remedial Action for ZigBee Signal Challenges  
#### 3.5.1 Network Interference and Security  
The security of the communication link is the function of signal strength of the channel characteristics and determines the error correction methods deployed by the terminal equipment. Whereas the signal strength of the channel influences the signal-to-noise ratio (SNR), it is an assurance of the channel transmitted signal quality. It secures signal transmission quality concerning path loss, weather constraints, and the terminal equipment interferences. ZigBee WSNs configuration applies AES 128 data security integrity check and authentication for access control and data encryption. Using AES-128 security algorithm according to IEEE 802.15.4 standard ensures signal security [55; 56; 57]. It guarantees ZigBee reliability for collision avoidance and also reserves the bandwidth of the communication link. The data sent then avoids competition and conflicts. ZigBee operates on the instrumentation, scientific and medical (ISM) radio bands standard. The IEEE 802.15.4 standard specifies the Physical (PHY) and Medium Access Control (MAC) layers on such frequency bands. The spectrum bands include 902-928 MHz (USA), 868-870 MHz (Europe), 433.05-434.79 MHz (the USA and Europe), and that of global band 2.400-2.4835 GHz (worldwide) [58; 60; 85]. As it has been specified, the spectrums are enabled, either globally or nationally with the direct sequence spread spectrum (DSSS) interface using BPSK techniques for 868 MHz and 915 MHz, and O-QPSK for 2.4 GHz spectrum categories. Again, the convergence access methods enable network for carrier sense multiple access with collision avoidance (CSMA-CA). The IEEE 802.15.4 PHY standard supports the inclusion of receiver energy detection (ED) with link quality indication (LQI) and clear channel assessment (CCA). These are contention-based and contention-free channel access methods of supported standards employing 64-bit IEEE and 16-bit short addresses to enhance more nodes per network applications. The IEEE 802.15.4 MAC standard also operates network association and disassociation, with an optional super frame architectural of beacons for time synchronization. The synchronization guarantees time slot (GTS) mechanism with high priority communications [57; 58; 59; 60; 61; 62; 68; 65; 67; 68; 69; 62; 86]. The ISM spectrum bands accommodate applications including Wi-Fi, Bluetooth, and others. This shared spectrum band serves as a medium to exhibit interference to ZigBee especially from Wi-Fi. ZigBee and Wi-Fi coexistence challenges on the ISM frequency band is considered to be communication techniques issue on the same spectrum allocation. There are modalities envisaged to address such signal conflict. The techniques resolve to have interference avoidance and mitigation schemes including frequency co-existence on the same spectrum as discussed in [58; 59; 85; 86; 87; 88]. ZigBee alliance supervises the ZigBee wireless technology, thus defining the network security and application layers relating to the IEEE 802.15.4 PHY and MAC layers standard. The MAC configuration safeguards data integrity by authenticating the source frame sequence and protects the source sending packets with enforcement encryption data unto the higher layers. It then adds frame sequence checks to identify transmission errors and process the data to the physical layer once the suitable channel access method is certified. The MAC techniques further control data transmission to avoid congestion and collisions particularly with similar topologies on the same spectrums where the collision of domain exists. Furthermore, MAC is similarly responsible for recompensing congestion and collisions by strategizing jam signal detection and negotiating retransmission channel and rate where applicable [58; 59; 85; 90; 91]. ZigBee has patterns to enable functioning schemes that allow application activities and performance throughput. They are categorized, as a full function device (FFD) and a reduced function device (RFD).