## 3 The FatBeacon Protocol
Since there is currently no device that implements the FatBeacon protocol natively, we have built it by an empirical data collection methodology. The way to obtain the data for BLE 4 has been by performing tests in a controlled environment using mobile devices such as a transmitter and a receiver. For this purpose, a Samsung Galaxy S7 mobile phone (model SM-G930F) has been used in the experiments as a transmitter and a Xiaomi Mi5s (model 3/64) as a data receiver. Both mobile phones have a Bluetooth version that allows the simulation of this new FatBeacon protocol. To simulate the data, the official Google Physical Web application [26] has been modified, making the necessary changes to carry out the experiments. The changes made to the original application have been as follows:  
* Modify the BluetoothSite.java adding the following variables privatelong start_time = 0; and private long end_time = 0;. * In the connect function, start_time = System.nanoTime(); was added
* start_time)/1e6; were added at the end of the function (with a System.out.println(difference) to check the result. The files with the transmitted HTML content were stored on the mobile device in order to make the different broadcasts depending on the size (see Table 1). With these files, having the mobile device connected to a laptop, it is possible to observe the different transmission times and measures from one terminal to another from the terminal. The other bit rates (BLE5 [27], 2G and 3G [28]) were extracted  
Figure 4: Differences between classical the Beacon and FatBeacon protocol. from the specifications of each type of connection, considering if the bit-rate is 1 Mbps = 0.125 MB/s. The resulting download times, taken for each kind of connection and size, are shown in Table 1.  
The connection times of BLE4 have been extracted from Table 2, obtained in the same way as the previous experiments, maintaining the distances between transmitters and receivers to 1 m. Five measurements were made for each web-page weight. Afterwards, in order to obtain more stable data, the best and worst data for each measurement were discarded, leaving an average of the remaining values as a reference value. Regarding the results shown in Table 2, the found correlation index (0.9468) between speed and load size is directly related to a strong relationship between those parameters. In order to determine whether the transfer time depends on the distance, another empirical test was performed in the same testing laboratory. This time, a static page size of approximately 40 kB and a variable distance were used. The experiment was carried out for each test in a straight line to avoid obstacles or other factors, such as wind, solar rays or other types of radiation such as WiFi signals, which impede the emission of the signal in the correct way. The results are displayed on Table 3.  
In the case shown in Table 3, the computed correlation index (0.6851) corresponding to the distance between the mobile phones and the transfer rate indicates that there is a relationship between them. Note that both the emission frequency and the emission power also depend on a strong correlation between each one of those variables and the emission angle. The work [29] includes an \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Packet Size** & **BLE4** & **BLE5** & **2G** & **3G** \\ \hline
10 kB & 5.21 & 1.30 & 5 & 0 \\
20 kB & 8.82 & 2.20 & 11 & 0 \\
40 kB & 7.43 & 1.85 & 23 & 0 \\
100 kB & 15.18 & 3.79 & 58 & 2 \\
200 kB & 28.14 & 7.03 & 107 & 4 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Download speeds in Mbps for different protocols and sizes. * Based on the BLE5 specifications; ** based on the Generation Partnership Project (3 GPP) specifications, without considering the Transmission Control Protocol (TCP) connection delay.