# Smartphone-Based Experimental Analysis of Rainfall Effects on LTE Signal Indicators
## 5 Data-Driven Analysis
### Rainfall Impact on Signal Measurements
#### 5.2.2 Frequency Difference for the Different Weather  
In Section 5.1, a daily variation pattern is observed. The uncertainties regarding when values change, and the extent of these changes complicate the estimation of variations and the separation of rain-induced fluctuations from those caused by other factors. Treating rainfall as an abnormal weather condition might disrupt the long-term pattern of signal measurements, potentially introducing more frequency components, which would be reflected as increased power at some frequencies in the PSD spectrum. Thus, the frequency domain has been utilized to analyze the impact of rainfall on signal measurements. To facilitate a comparison of the PSD during rainy and dry periods, we apply the Fourier transform to an equal number of samples, 48 (2 days), from different weather conditions. The PSD is normalized by dividing the total power across all frequencies and converting the result to decibels unit. Two examples of signal measurements for dry days, along with their normalized power spectral density (NPSD) spectra, are presented in Figure 11. The NPSDs exhibit a tailing trend; generally, higher frequencies correspond to lower power levels. This drop is more pronounced in RSSI and RSRP measurements compared to RSRQ and SNR, signifying a greater disparity in power across different frequency components. To compare the PSD during rainy and dry periods, the NPSD for rainy days is divided by the NPSD for dry days, resulting in a subtraction betw  
Figure 11: Hourly average signal measurements and NPSD spectrum during dry days: (**a**) 4–6 December. (**b**) 3–5 March. expressed in decibels (dB). The difference between the NPSD values for rainy and dry conditions being greater than zero indicates more power during rain than during dry conditions at that frequency. The NPSD during rainy days and the NPSD difference between the rainy and dry periods from different datasets are shown in the figures below. Figures 12 and 13 illustrate the NPSD and the differences between rain events and dry periods in Dataset 1. Two reference dry periods are from 4 December to 6 December and from 3 March to 5 March, as indicated in the legend. For frequencies lower than 0.0417 (\(\times\)1/3600) Hz, the power of RSSI and SNR measurements during rainy days is higher than that observed on the reference dry day, as depicted in these figures. Figure 12: Signal measurements during rain (18–20 December): (**a**) NPSD for signal measurements. (**b**) RSSI power difference of NPSD between rainy days and dry days. (**c**) RSRP power difference of NPSD between rainy days and dry days. (**d**) RSRQ power difference of NPSD between rainy days and dry days. (**e**) SNR power difference of NPSD between rainy days and dry days. Figure 13: Signal measurements during rain (30 December 2023–1 January 2024): (**a**) NPSD for signal measurements. (**b**) RSSI power difference of NPSD between rainy days and dry days. (**c**) RSRP power difference of NPSD between rainy days and dry days. (**d**) RSRQ power difference of NPSD between rainy days and dry days. (**e**) SNR power difference of NPSD between rainy days and dry days. There are two major rain events in Dataset2, from 4 April 2024 to 6 April 2024 and from 10 May 2024 to 11 May 2024. The NPSD and the difference of NPSD between the rainy and the dry period are shown in Figure 14 and Figure 15, respectively. Here, two reference dry periods are selected, from 10 April 12 p.m. to 12 April 12 p.m. and 18 May 12 p.m. to 20 May 12 p.m. The power for RSSI and SNR measurements on rainy days is higher than that of the reference dry day for frequencies below 0.0417 (\(\times\)1/3600) Hz. Generally, there is more power at lower frequencies, specifically below 0.15 (\(\times\)1/3600) Hz, in hourly average RSSI measurements, except at 0.0417 (\(\times\)1/3600) Hz. Additionally, the hourly average RSRP measurement shows greater power in the range of 0.1 to 0.3 (\(\times\)1/3600) Hz during rain compared to dry conditions.