# Wireless Channel Models for Over-the-Sea Communication: A Comparative Study
## 6 Possible Applications and Improvements
### Insights on Modeling the Over-the-Sea Wireless Channels  
In this subsection, some critical issues, prospects, and phenomena are addressed and discussed in order to share our insights with readers. **Scattering of the sea waves:** Scattering of electromagnetic waves is a key factor in wireless channel modeling for over-the-sea communication. It puts a great impact on the multipath fading of a channel. Obstructions are not frequent and dense in the sea. Sparse scattering holds most of \begin{table}
\begin{tabular}{c c} \hline \hline
**Channel Model** & **Possible Future Improvements** \\ \hline Ref. [8] & Multipath effects of the sea surface may be incorporated into the channel model in the future to make it more reliable. \\ Ref. [9] & Elevated duct-based channel measurements may be included. \\ Ref. [10] & Diffuse and specular multipath propagations may be introduced in this channel model in the future. \\ Ref. [11] & The channel model can be improved by taking into account the error rate along with the signal strength as a parameter. \\ Ref. [12] & Sea roughness can be included as a channel modeling parameter. \\ Ref. [5] & A propagation loss model can be introduced. \\ Ref. [13] & A complete fading margin calculation may be introduced, consisting of slow and fast fading. \\ Ref. [14] & Technical validation of the mathematical idea should be introduced in the future. \\ Ref. [15] & Channel evaluation parameters, such as mean excess delay, fade margin, etc., can be introduced for a reliable design. \\ Ref. [16] & Channel evaluation parameters, such as mean excess delay, fade margin, etc., can be introduced for a reliable design. \\ Ref. [17] & Channel model can be integrated to support nLoS or bLoS propagations. \\ Ref. [18] & Channel model should be integrated with complex real time path loss model and duct effects. \\ Ref. [19] & Fade margin determination can be introduced in the model. \\ Ref. [20] & Fade margin determination can be introduced in the model. \\ Ref. [21] & Sea surface can be designed in a 3-D cross section. \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Possible future improvements of the channel models. the channel links including the air-to-sea, ship-to-ship, or land-to-ship channels. Because Rayleigh fading is very commonly used for terrestrial channel modeling, it is not suitable for sea surface channel modeling. The scattering model proposed in [50; 51] can be used. **Suitability of the two-ray model:** In Section 2 of this paper, we introduced a two-ray path loss model [6]. Two paths are highly important for designing a wireless channel model. One ray is the LoS path and the other is the reflected path. The two-ray model is a good approximation when we have a bigger antenna height. If the antenna height is low, scattering of rays will display more randomness in the channel. For this kind of scenario, more paths are necessary to be taken into consideration. **Impact of Tx-Rx distance:** Widely distributed transmitters (Tx) and receivers (Rx) have an impact on the angle domain. It is possible that the LoS path and the sea surface reflection path have identical angular directions. When the distance between the Tx and Rx increases, the angle difference between these two paths decreases. If multiple antenna arrays are set either in the transmitting end or in the receiving end, it may cause high correlation between the antenna elements. This may result in a rank-deficient MIMO channel matrix. When the Tx-Rx distance is short, the channel can be modeled by using the classic two-ray model [6]. As the distance increases, a three-ray model [7] becomes more suitable. When the receiver continuously moves far away, LoS and surface reflection paths vanish due to the curvature of the Earth. It is still possible that the receiver can hear from the transmitter in the presence of the duct layer. **Effects of the sea wave movement:** Sea wave movement has a great impact on radio wave propagation. It is especially dominant for surface reflection paths.