# Underwater Communications for Video Surveillance Systems at 2.4 GHz
## 3 Scenario and Test Bench
### Preliminary Tests to Characterize the Video Transmission  
In order to specify the minimum requirements of the communication channel, the first step is to define the requirements that the file we want to transmit needs, so have done a preliminary test where a SJCAM5000 WiFi action camera [25] has been used. It is a small camera capable of recording images in full HD quality and transmits its signal via Wi-Fi. The SJCAM 5000 WIFI uses the optical sensor MN34110 PA developed by Panasonic Corporation [26] with a photograph resolution of 14 Mpx. This camera usually works with the following resolutions: 1080 p at 30 fps and 720 p at 60 fps. During the tests, we have used many video resolutions in order to make this study useful for many other cameras.  
As file to be sent, we have used a video of 50 s long compressed with the H.264 codec, which gives as a result an mp4 file format. We have used various resolutions as well as two frame frequency commonly used in this type of cameras. Table 1 summarizes the configuration parameters for the video used in this test.  
To perform these tests we have used the action camera and a miniPC executing a lightweight OS based on linux. This kind of device is able to work as a personal computer with the same functions, but its size is around a cube of 10 \(\times\) 10 \(\times\) 10 cm\({}^{3}\) this device will serve us as a gathering system [27]. Both devices are connected through a point-to-point wireless connection. The camera records video and send it to the miniPC which monitors the network activity (see Figure 1). To register network activity, the miniPC runs Wireshark Network Analyzer [28] and NetMeter [29].  
The first parameter to be measured is the size of file we send through the network as a function of the resolution and the frame frequency. Figure 2 shows the size of file sent thro  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Frame Frequency** & **Parameter** & **Value** \\ \hline \multirow{4}{*}{30 fps} & Resolution & 800 \(\times\) 600; 852 \(\times\) 480; 1024 \(\times\) 768; 1280 \(\times\) 720; 1280 \(\times\) 1024; \\  & Resolution & 1408 \(\times\) 1152; 1600 \(\times\) 1200; 1920 \(\times\) 1080 \\  & File format & *.mp4 \\  & Bit Rate & Variable \\ \hline \multirow{4}{*}{60 fps} & Resolution & 800 \(\times\) 600; 852 \(\times\) 480; 1024 \(\times\) 768; 1280 \(\times\) 720; 1280 \(\times\) 1024; \\  & Resolution & 1408 \(\times\) 1152; 1600 \(\times\) 1200; 1920 \(\times\) 1080 \\ \cline{1-1}  & File format & *.mp4 \\ \cline{1-1}  & Bit Rate & Variable \\ \hline \hline \end{tabular}
\end{table}
Table 1: Parameters of videos.  
Figure 1: Test bench for video characterization.  
The most noteworthy aspect is that for a given resolution, having a double frame frequency does not mean having a twice bigger file. Figure 3 shows the bandwidth in Mbps as a function of time for each video resolution when they are transmitter at 30 fps. As we can see, the maximum bandwidth (7 Mbps) is registered for the biggest resolution (1920 \(\times\) 1080).  
Figure 4 shows the bandwidth in Mbps for each video resolution when they are transmitted at 60 fps. In this case, the maximum bandwidth is about 8.5 Mbps and it is obviously registered for the biggest resolution (1920 \(\times\) 1080).  
Figure 4: Bandwidth for videos at 60 fps.  
Figure 3: Bandwidth for videos at 30 fps.  
Figure 2: Size of files in MB.  
Finally, Figure 5 shows the maximum and average data transfer rate for each video at 30 fps and 60 fps. If we are unable to guarantee these values, at certain times the video will be received with errors and will suffer cuts and interrupts.  
As we have seen in previous studies [15], the acoustic waves do not guarantee enough bandwidth to transmit such content, so we need to increase it and for this reason, we want to study the behavior of EM waves. This is the method with low cost of implementation that permits the video transmission.