# Measurement and Analysis of RSS Using Bluetooth Mesh Network for Localization Applications
## 5 Analysis of RSS Measurements Using Bluetooth Mesh Network
### Small-Scale Multipath Fading  
To examine the small-scale multipath fading effects in indoor environments, we placed the transmitter (i.e., beacon node) and receiver (i.e., scanner node) devices (both with the external 6 dBi omnidirectional antenna) by 4 m apart and conducted two experiments. In the first experiment, receiver antenna is installed at the position P1 of the measurement platform shown in Figure 7. The platform is rotated to six different angular positions with an angular step of 60\({}^{\circ}\) while the rotation center of the measurement platform is at the point P0. Such a measurement process is equivalent to moving the receiver antenna to each of the positions from P1 to P6 without rotating the measurement platform. At each angular position, 20 measurements are collected from each of the three advertising channels and the RSS measurement results are shown in Figure 10. From the results, we can observe that the RSS measurement data collected from different advertising channels undergo different attenuation and fading effects. In addition, small positional shifts caused by rotating the antenna around P0 result in variations as large as 15 to 20 dB in  
Figure 8: Directionality of ESP32 with the onboard PCB antenna. RSS measurements in dBm unit collected at different angular positions are plotted in different colors with red for channel 37, green for channel 38, and blue for channel 39. Transmitter and receiver devices are 1 m apart in distance.  
RSS measurements. If not compensated properly, such small-scale fading will introduce large fitting errors and uncertainty in path loss models. Typically, in path loss modeling, the small-scale fading is averaged out with multiple measurements in close vicinity of each measurement location with small random positional shifts. Multiple measurements can also be collected at each location in a more systematic way similar to our measurement setup with a rotating platform.  
However, taking multiple measurements using one receiver device in local vicinity of every location is rather cumbersome in practice. To address this issue, in this research, we installed six receivers on the measurement platform with their antennas positioned at P1-P6 shown in Figure 7. During measurement, for each packet transmitted by the transmitter device, six receivers will receive and measure the RSS simultaneously and the measurement data are forwarded to the sink node using the Bluetooth mesh networking protocol. As described in Section 4.3, the advertising message contains a message sequence ID number in the payload, which is used in postprocessing to match the RSS measurements collected simultaneously from multiple receiver nodes. A sample measurement result is shown in Figure 11, where variations (i.e., small-scale fading effects) among six receivers are clearly visible. In postprocessing for path loss modeling, the data collected from six receivers are averaged (or, more accurately, combined as discussed in the next section) to eliminate the random variations caused by small-scale fading effects.  
Figure 10: RSS measurements in dBm unit using one receiver antenna at the positions from P1 to P6 on the measurement platform. Transmitter and receiver devices are 4 m apart in distance and both devices use the external 6 dBi omnidirectional antenna.  
Figure 9: Directionality of ESP32 with the external 6 dBi omnidirectional antenna. RSS measurements in dBm unit collected at different angular positions are plotted in different colors with red for channel 37, green for channel 38, and blue for channel 39. Transmitter and receiver devices are 1 m apart in distance.