## 2 Related Work  
Generally, UW-WCSs use acoustic signals, which are low frequencies in comparison to the other frequencies used for UW communication. There are many papers discussing the propagation scenarios for acoustic waves in underwater communication and applications [1; 2; 4; 5]. Thus, the challenge is to work on high frequency bands (in the range of GHz) for underwater communication and applications, which is an open area for the researchers. There are many authors who have researched about the medium characteristics and also illustrated the comparative study over the various frequencies used for underwater wireless communication such as acoustic, radio and optical signals in UW environments.  
In [6], the authors have analyzed path loss by reflection and refraction of the acoustic signals in underwater environment. In [4], the authors have worked on estimating the effects of depth of water and effects of temperature over acoustic frequencies. The authors in [7] presented a detailed description relating various parameters of high frequency waves (2.4 GHz) such as propagation velocity, total path loss, wavelength and frequency with different values of distance and conductivity of the water medium for UWSNs. They focused on using high frequency EM wave propagation and characterizing  
Figure 1: Generic underwater sensor network architecture [3].  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Carrier** & **Transmission Distance** & **Bandwidth** & **Mode of Communication** \\ \hline Accoustics & 1000 km & \(<\)1 kHz & Non Line of Sight \\ Radio & \(<\)1 m & 1 MHz & Non Line of Sight \\ Optical & \(<\)10 m & 1 GHz & Line of Sight \\ \hline \hline \end{tabular}
\end{table}
Table 1: Underwater wireless communication systems.  
the channel with magnetic permeability, di-electric permeability and permittivity, electric conductivity and volume charge density of the water medium.  
In [10], the authors performed simulations with 3 kHz for underwater communication and achieved distances of around 40 m between the communicating nodes. In [12], the authors also tested multiple frequencies and estimated maximum distances. At 100, 10 and 1 kHz, the maximum distances traveled were 6, 16 and 22 m, respectively.  
In [13], the authors have developed an initial design of Field-Programmable Gate Array (FPGA) based underwater high frequency (ranging from 100 kHz to 1 MHz) acoustic modem for short distance communication. Utilizing the greater bandwidth of this frequency, the authors have been able to achieve substantially better results for shorter distances in terms of symbols per signal. The modem employed Binary Phase-Shift Keying (BPSK) modulation, with a transmission rate of 1 kbps of data rate with a duration of around 1 ms and a wait time of 20 ms. They stated that it is an appropriate interval to avoid the effects of reflections under water.  
In [14], the authors discouraged the use of RF band for UW communication and have used the Very Low Frequency (VLF) band of the electromagnetic spectrum as it does not suffer more attenuation as compared to other higher frequencies. The authors stated that the high attenuation is due to the conductive water medium. In addition, they reported 2.4 GHz frequency band as an invalid band for UW communications. Though high frequency EM signals do offer higher throughput as compared to acoustic signals, but the order of attenuation is very severe in UW communication systems.  
Much less research has been done on estimating underwater transmission loss or path loss at 2.4 GHz [15]. Therefore, this paper focuses on estimating path loss for 2.4 GHz frequency band for UW-WCSs. We further extend our work to different UW environments, absorption loss estimation and possible effects of water conductivity over 2.4 GHz bands. By transmitting at 2.4 GHz in UW environments, this paper justifies the use of 2.4 GHz bands in certain scenarios rather than proclaiming it to be a totally invalid band for UWSNs like in [14] and also proposes underwater applications using 2.4 GHz.