# Radio Channel Modelling for VHF System Operating in the Offshore Wind Farms Propagation Environment
## 3 Results and Discussion
### Simulations for Systems Operating in the VHF Band in the Marine Environment of Wind Farms
The impact of the wind farm on the ship's reference communication system also depends on the distance from the wind farm, as can be seen in Figure 13. Assuming that the  
Figure 13: CIR plots for reference communication system transmitting from the ship at different distances from the wind farm, for different wind farm configurations and 3 m turbine tower radius: (a) 25 turbines (5 \(\times\) 5) and ship at distance of 500 m; (b) 25 turbines (5 \(\times\) 5) and ship at distance of 2 Nm; (c) 25 turbines (5 \(\times\) 5) and ship at distance of 10 Nm; (d) 100 turbines (10 \(\times\) 10) and ship at distance of 500 m; (e) 100 turbines (10 \(\times\) 10) and ship at distance of 2 Nm; (f) 100 turbines (10 \(\times\) 10) and ship at distance of 10 Nm. acceptable reference communication system CIR level is 10 dB, then seven of ten areas on the presented CIR plots will represents the areas with no coverage, where the interference criteria is not meet and the continuous radio communication is not possible. The size of other (3 of 10) coverage areas increases as the distance between ship and wind turbines increases, which can be seen in Figure 13 (c vs. b vs. a, and f vs. e vs. d). It is also worth nothing, that at large distances (10 Nm), both simulated wind farms-- the large one (100 turbines 10 \(\times\) 10) and the smaller one (25 turbines 5 \(\times\) 5)--have a similar impact on the reference communication system coverage area, as can be seen in Figure 13 (_c_ vs. _f_). To sum this up, the most unfavorable results were observed in the following situations:  
When the ship was further from the farm;  
For a farm consisting of a larger number of turbines;  
For a farm with a larger average tower radius. While this may seem surprising, it is fully in line with the specifics of the Annex 2 propagation model from the recommendation [11]. According to this document, the size of the effective reflection area of the turbine is directly proportional to the distance from the transmitter (see formula 25). Thus, when the ship was close to the wind farm, the reflecting surface of the turbines (de facto: the mast) was smaller compared to the case when it was located 10 Nm away from the farm. Obviously, the larger the reflecting surface, the higher the potential negative impact of the power plant on the radio signal--which is directly confirmed by the simulation results presented above. The second reason is that the width of the Fresnel zone radius increases with the distance, so in the case of ship-to-ship communication (antennas at a relatively low height compared to the turbine) the attenuation between the transmitter and receiver will always be greater (due to diffraction) than between the receiver and the wind turbine, assuming the same length of the propagation path. Conducting a simulation of radio planning is very important, first of all to check whether the range of the useful signal in the presence of an offshore farm is sufficient and whether necessary corrective actions should be taken to eliminate negative impacts of the wind farm on systems operating in the marine VHF band.