The need for reliable and uninterrupted communication systems in the marine environment has become critically important with increasing maritime activities, environmental monitoring, and the spread of autonomous systems. However, the complex structure of electromagnetic wave propagation in a sea environment limits the accuracy of the existing propagation models. Thus, the Modified Round Earth Loss (REL) model was first developed in this study to estimate the path loss more accurately in shore-to-ship communication. Subsequently, a piecewise modeling approach based on the principle of two-segment data modeling was proposed. In the Modified REL model, unlike the traditional REL model, the paths and gains of the direct and reflected waves were not considered equal in the calculations. Moreover, unlike in the classical approach, the receiver height was not taken as a fixed value; the estimated best receiver height value for each measurement was included in the calculations as a representation of the effect of roughness in the sea environment. Thus, the model is better adapted to various environmental conditions. In addition, the proposed piecewise model divides the propagation medium into two regions using a break point calculated by Fresnel zone theory. The Modified REL model was used for the first region and the log-distance model was used for the second region. This method allows for more accurate modeling of signal behaviors, especially at different distances. Experimental measurements and performance evaluations conducted using four different shore-to-ship communication scenarios show that the Modified REL model shows an average improvement of up to 3% in Root Mean Square Error (RMSE) values compared to the classical REL model. Additionally, the proposed piecewise model improves the fitting error of the Modified REL model, which models the data as a single whole, by an average of 22.25%. These findings emphasize the necessity of propagation models that are sensitive and adaptable to environmental changes for maritime communication.

Araçlar arası (V2V) haberleşme, karayolu sürüş güvenliği ve kaza önleme açısından önemli bir teknoloji olarak görülmektedir. Ancak, araçlar arasına giren binalar, diğer araçlar ve ağaçlar gibi çevresel engeller V2V haberleşmeyi olumsuz yönde etkileyebilmektedir. Bu çalışmada, virajlı dağlık anayol ortamlarında, verici ve alıcı araçlar arasındaki iletişimi engelleyen dağlık alanların etkisi incelenmiş ve 5.9 GHz’de V2V ölçümleri yapılmıştır. Ölçülen veriler, engel senaryolarında yaygın kullanılan log-normal ve çift eğimli yol kaybı modelleriyle modellenmiş ve verilere uyum performansları açısından karşılaştırılmıştır. Sonuçlar, dağ engeli bulunan senaryolarda çift eğimli yol kaybı modelinin daha iyi bir uyum sağladığını göstermektedir. Ayrıca, dağ engelinin neden olduğu gölgeleme ve zayıflatma etkileri incelenmiş, dağ engeli kaynaklı ortalama zayıflamanın 19.6 dB olduğu tespit edilmiş ve literatüre ilk kez bu çalışma ile kazandırılmıştır. Bu bulgular, sistem tasarımcıları ve araştırmacılarına çevresel faktörlerin V2V iletişim performansına etkisinin detaylandırılmasında ve sistemlerin buna göre optimize edilip tasarlanmasında katkı sağlayacaktır.

Vehicle-to-Vehicle (V2V) communication channel measurements were carried out in different environments such as urban, suburban, rural, highway, tunnel, and overpass. The roads in these environments have generally flat terrain. However, there are horizontal or vertical curve roads that have been little focused in the literature. In this study, we performed two V2V measurements on a vertical-curve road in a rural environment to show how received signal strength changes with the distance between the transmitter and the receiver. The path loss exponent of log-distance path loss model was calculated by using the least-square method. According to the results, the path loss exponents were estimated as 7.53 and 7.61 with 78% and 83% fitting performances for two measurements. In literature, however, the path loss exponent for different propagation environments was obtained up to 6.13, especially in the straight road. Thus, our findings show that the vertical curve roads cause 15-20 dB more attenuation in the received signal strength than the straight roads. As a result, the vertical curve roads should be investigated and included in existing wireless communication simulators to better model real measurements. The authors contend that this study will aid in improving the channel modeling of V2V communication.