In this example we use the UCFDTD model to simulate radio wave propagation in Ottawa , Canada.
Once again, we consider the section of Ottawa depicted in Figure 1 and we use the transmitter located on Slater Street . We simulate the propagation of a pulse with frequency centered at 150 MHz and with a Blackman envelope. We will then compare the results of the UCFDTD simulations with the results of the Urban Canyon model. Figure 1 shows the project view of Ottawa with transmitter and receiver sets.
Since the UCFDTD model is designed to simulate the propagation of transient pulses, we create a new vertically polarized waveform with center frequency of 150 MHz, and with a Blackman envelope with pulse width of 0.06 micro seconds. Figure 2 shows the waveform properties.
We choose the transmitter located on Slater Street and associate the new Blackman waveform to the transmitter and all the receivers. Then, double click on the study area entry in the main window will bring up the study area properties window. Change the propagation model to Urban Canyon FDTD. Alternatively, you can create a separate study area for UCFDTD model. The resulting study area window is shown in Figure 3.
Notice that there are two parameters that the user can change for the UCFDTD model. The first is cells per wavelength. It determines the size of the cell spacing for the finite difference grid. The larger the cells per wavelength, the longer the simulation will run. Generally, cells per wavelength should be no smaller than 10. Alternatively, the user can check the automatic box and let the program determine this number. For this simulation we set cells per wavelength to 10. The second parameter is total time. This is the total amount of time the radio wave will propagate through the city, not the amount of time the simulation will take. For this example we check the automatic box and let the program decide the total time.
Once all the parameters have been set, click on Project>Run>New to launch the calculation engine. A word of caution: the UCFDTD simulation will take several hours to complete, so the user should take that into account when running a calculation.
In Figure 4, Figure 5, and Figure 6 we plot the path gain calculated by UCFDTD along Laurier Street , Albert Street , and Queen Street , respectively. For comparison, we also plot the result calculated using the Urban Canyon model. As can be seen from the figure, the UCFDTD results agree well with the Urban Canyon results. Since the two models are so different, the fact that they agree so well gives a high degree of confidence that the results are correct. In Figure 7, we also plot the area coverage prediction calculated by UCFDTD.
- J. H. Tarng, W. Liu, Y. Huang, and J. Huang,