# Underwater Electromagnetic Sensor Networks--Part I: Link Characterization +
## 4 Discussion and Conclusions  
In this paper, a full description of a testbed for underwater communications in a real environment is provided. Moreover, a characterization of the underwater link in the frequency domain has been obtained after carrying out several measurements in underwater scenarios with dipole and loop antennas, obtaining enough information to decide some basic parameters of the communication system. Since good agreement between measurements and simulation results has been achieved, simulation tools and their setup parameters have been validated. Therefore, further experiments can be simulated.  
Thanks to this study, several important results have been obtained, making possible the design of the physical layer of the UWSN. Loop antennas were found to be the most useful ones for shallow waters. Moreover, a 40 cm radius can be an adequate size, as there are considerably lower losses than with 22 cm, and it is not too large to be used in a UWSN. Frequency response figures between 10 KHz to 1 MHz for different distances have been provided, making these results a useful tool for further research on the field. Possible carrier frequencies for sensor nodes and maximum distances that can be reached have been simulated.  
Regarding future research lines, the next step is to carry out experiments with ferrite antennas, which are being designed at the moment, and may offer the same performance with a smaller form factor. Furthermore, node prototypes for the UWSN are currently in development.  
**Acknowledgments:** The authors would like to thank [PERSON] (ULPGC) for the work carried out when making the pressurized PVC receptacles, loop antennas and all of the lab materials needed to make the measurements. Furthermore, the authors would like to thank [PERSON] and [PERSON] (PLOCAN) for the work related to setting up measurement testbeds on the pier and underwater. This work has been supported by Ministerio de Economia y Competitividad, Madrid, Spain, under public contract TEC2013-46011-C3 and TEC2016-76038-C3.  
**Author Contributions:** [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] designed and constructed the transmitter and receiver chambers, and also built the testbed. [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] performed the underwater measurements. [PERSON], [PERSON] and [PERSON] performed the simulations and designed antennas. [PERSON]  
Figure 15: Amplitude time evolution during a 2 h time period.  
and [PERSON] wrote the article. All authors made contributions to this paper. [PERSON] and [PERSON] coordinated the project.  
The authors declare no conflict of interest. Founding sponsors took no part in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.  
The following abbreviations are used in this manuscript:  
UWSNs Underwater Wireless Sensor Networks EM Electromagnetic MoM Method of Moments PVC Polyvinyl chloride RF Radio Frequency UTP Unshielded Twisted Pair DC Direct Current FEKO FFLdberechnung fur Korper mit beliebiger Oberflache RBW Resolution Bandwidth