## 4 Data Analysis and IBC Channel Gain Characteristics  
For data analysis, we used the dataset \"all_measurements_by_freq_filtered.csv\" from [21], as it contains key results for a single frequency in each row, and noise was cleaned from it. The dataset consists of data in the frequency range of 50 kHz to 20 MHz. Figure 1 shows the dependence of IBC channel gain on the signal transmission frequency. Based on the analysis, we identified the most suitable frequency for signal transmission at 12.5 MHz.  
We analyzed only data measured at a frequency of 12.5 MHz from the first experiment. All measurements were carried out under the same environmental conditions and at the same time, and they also contain the largest number of measurements compared to other experiments. The frequency of 12.5 MHz has the lowest signal attenuation (Figure 1); therefore, that frequency is the most suitable for signal transmission. We analyzed 616 measurements in our study.  
Figure 1: Receiver gain dependence on the signal transmission frequency.  
In Figure 2, the dependence of the receiver gain on the individual subject body parameters is presented. The gain of the receiver for a 50 \(\Omega\) load is in the range \(-38.8\) to \(-46.0\) dB, and for a 1 m\(\Omega\) load \(-31.2\) to \(-37.4\) dB. Based on the dataset analysis, we concluded that the IBC channel gain depends on the subject's individual characteristics. As shown in Figure 3, the receiver gain depends on the subject's height and is in the range \(-29.0\) to \(-46.0\) dB for a 50 \(\Omega\) load and \(-31.8\) to \(-37.4\) dB for a 1 m\(\Omega\) load. Figure 4 shows the dependence of the receiver gain on the subject's weight. The gain of the receiver for a 50 \(\Omega\) load is in the range \(-23.6\) to \(-46.0\) dB, and for a 1 m\(\Omega\) load \(-31.2\) to \(-37.4\) dB. As shown in Figure 5, the receiver gain depends on the subject's body mass index and is in the range \(-21.2\) to \(-44.9\) dB for a 50 \(\Omega\) load and \(-32.5\) to \(-35.8\) dB for a 1 m\(\Omega\) load. Figure 6 shows the dependence of the receiver gain on the subject's body fat composition. The gain of the receiver for a 50 \(\Omega\) load is in the range \(-19.6\) to \(-45.2\) dB, and for a 1 m\(\Omega\) load \(-31.8\) to \(-36.9\) dB. As shown in Figure 7, the receiver gain depends on the sum of the fat levels at the transmit and receive points and ranges from \(-25.6\) to \(-39.6\) dB for a 50 \(\Omega\) load and \(-30.9\) to \(-36.5\) dB for a 1 m\(\Omega\) load.  
As shown in Figures 3-7, the receiver gain varies over a wide range depending on the subject's body characteristics; therefore, the IBC channel gain is influenced by height, weight, body mass index, and body fat composition. These indicators form a channel gain profile that can be used to identify IBC system users. In case of any changes in the human body, those changes are recorded in the database, and further, the accumulated changes are analyzed by the system in order to predict possible changes in the future. One of the major findings is that it is possible to arrange biometric identity using the individual human body characteristics in IBC.  
Figure 3: Receiver gain dependence on the subject height.  
Figure 2: Receiver gain dependence on the subject.  
Figure 4: Receiver gain dependence on the subject weight.  
Figure 5: Receiver gain dependence on the subject body mass index.  
Figure 6: Receiver gain dependence on the subject body fat composition.  
Figure 7: Receiver gain dependence on the sum of the fat levels at the transmit and receive points.