## 4 Performance Analysis of QoS Metrics
### RSSI Analysis for Indoor and Outdoor Multi-Hop Communication  
RSSI is one of the metrics used to determine the link quality between the transmitter and the receiver. Understanding this metric is essential to having a clear idea about the transmission range and sensitivity of the deployed network. This would facilitate to better localize the nodes in the network with energy optimization and reliability. The comparative study of the parameters, such as a signal to interference and noise ratio (SINR), link quality indicator (LQI), along with RSSI, would have given better understanding of the overall link quality. However, this study focuses only on the RSSI readings to analyze the link quality. Along with the other factors, RSSI depends primarily on the transmission power level and obstruction between the sender and receiver, transmission distance, and interference. Thus, it is expected to have varied RSSI readings with the change of transmission power, the number of hops, the distance between the end node and coordinator, and the deployment environment. For RSSI measurement in the indoor scenario, the nodes are deployed in an office environment as described in Figure 4. The coordinator is placed at position C\({}_{1}\) and RSSI  
Figure 8: End node lifetime estimation of XBee S2C with 5000 mAh battery at various packet intervals: (a) AES encrypted communication; (b) unencrypted communication. readings are taken by deploying the end nodes at 0, 5, 10, 15, 20, 25, 30, 35, and 40 m from the coordinator corresponding to the C\({}_{1}\), E\({}_{5}\), E\({}_{10}\), E\({}_{15}\), E\({}_{20}\), E\({}_{25}\), E\({}_{30}\), E\({}_{35}\), and E\({}_{40}\) annotation of Figure 4. We should note that for all of the cases no line of sight was maintained with obstructions, such as a concrete wall, lab equipment, and machinery. For an outdoor environment, the coordinator is placed at the center of an open parking area and the end nodes around it with distances ranging from 0 to 40 m with a direct line of sight for all the cases. At every point of measurement for all the instances, a mean of 50 readings is taken into consideration. Figure 9 presents the link quality of transmission in terms of RSSI with different transmission power levels, distances, and deployment environments. In both the deployment scenarios: indoors and outdoors, the link quality with the transmission power level of 5 dBm is the best and that of 1 dBm is the worst. In the indoor office environment, the values fluctuate more in comparison to the outdoor scenario, due to the NLoS transmission medium. However, it follows the same trend for all the transmission power levels, which ranges from \(-40\) to \(-92\) dBm for P\({}_{\text{Trans}}\) = 5 dBm and from \(-40\) to \(-97\) dBm for P\({}_{\text{trans}}\) = 1 dBm in the indoor scenario. Comparatively, the link quality is better in the outdoor scenario with RSSI ranging from \(-35\) to \(-71\) dBm for P\({}_{\text{trans}}\) = 5 dBm and from \(-36\) to \(-82\) dBm for P\({}_{\text{Trans}}\) = 1 dBm. The link of the outdoor scenario is better than that of the indoor office environment as it offers an LoS transmission medium with less interference and no obstruction in between. We should note that the RSSI performances of both the indoor and outdoor environments are good enough in comparison to the receiver sensitivity of the XBee S2C module of \(-100\) dBm. It would be more interesting to analyze the RSSI measurements of multi-hop communication in comparison with the single hop. For two-hop communication, one router node is placed at an equidistance from the coordinator and end node as presented in Figure 3. To analyze and compare the link quality of single-hop and two-hop communication for both indoor and outdoor scenarios, the study focuses only on the transmission power level of 3 dBm as it is most optimized. Figure 10 depicts the RSSI values of single-hop and two-hop communication with P\({}_{\text{Trans}}\) = 3 dBm for various transmission distance and deployment scenarios.