# Path Loss Measurement of Outdoor Wireless Channel in D-band
## 4 Results  
Figure 5a-g show the path loss samples at 7 different frequency points with a range of 138 GHz-163.2 GHz using the path loss models of FI, CI, and FSPL. To make the figures look clear, 10 measured path loss samples at each distance we taken and averaged, and the averages are presented by the diamonds. It can be observed that the experimentally measured path loss is greater than the theoretical path loss value in free space at all frequency points. The fitting results of the two models are similar and basically coincide at 138 GHz. We can observe that our measurements at 138 GHz agree with FI, CI, and FSPL models. The measured path loss fluctuates more as frequency and distance increase. The measured path loss curves deviate from the free space path loss curves up to 13.1 dB at 163.2 GHz. At the other frequencies, our measurements imply less differences from the FSPL model. Figure 6 shows the path loss at distances of 400 m and 800 m.  
Figure 4: (**a**) Satellite map of D-band transmission 800 m wireless link on Fudan campus; (**b**) photo of Tx-side; (**c**) photo of Rx-side. Figure 5: _Cont._Figure 5: Path loss at 7 frequency points. The diamond represents the path loss sample at a certain distance, and the dotted, dot, and solid lines represent the FI, CI, and FSPL models, respectively. (**a**) 138 GHz; (**b**) 139.2 GHz; (**c**) 145.2 GHz; (**d**) 150 GHz; (**e**) 154.8 GHz; (**f**) 160.8 GHz; (**g**) 163.8 GHz. Figure 6: Path loss at distances of 400 m and 800 m.  
To describe MMW signal path attenuation in D-band as a function of distance under different frequency points in outdoor environments, we estimated the path loss model parameters of the FI and CI models, which are given in Table 3. The CI model has no significant statistical difference compared to FI model, as described in the theoretical analysis. It can be seen that the \(\beta\) parameter of the FI model is around 2 at all frequencies. This differs slightly from the theoretical free space path loss exponent of 2, but its frequency dependence is insignificant. The minimum path loss index is 1.82 at 160.8 GHz, and the maximum path loss index is 2.33 at both 150 GHz and 154.8 GHz. The parameters of the CI model are greater than 2 at all frequency points, the minimum is 2.06 at 138 GHz, and the maximum is 2.47 at 163.2 GHz. Figure 7 demonstrates the variation of the reference distance path loss and path loss exponent at different frequencies in CI and FI models. Many factors can lead to instability in measurement campaigns. Firstly, the path loss exponent of the test band is extremely sensitive to scatter differences in the measurement \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Frequency**} & \multicolumn{3}{c}{**FI Model**} & \multicolumn{3}{c}{**CI Model**} \\ \cline{2-7}  & **\(\alpha\)** & \(\beta\) & \(\sigma^{\text{FI}}\) & _FSPL (f,d\({}_{\text{D}}\))_ & \(\beta\) & \(\sigma^{\text{CI}}\) \\ \hline
138 & 79.19 & 1.91 & 1.75 & 75.25 & 2.06 & 1.98 \\
139.2 & 82.45 & 1.88 & 0.87 & 75.31 & 2.16 & 0.33 \\
145.2 & 80.66 & 2.06 & 1.68 & 75.68 & 2.26 & 2.33 \\
150 & 72.7 & 2.33 & 3.33 & 75.96 & 2.40 & 2.63 \\
154.8 & 77.95 & 2.33 & 2.46 & 76.24 & 2.20 & 2.51 \\
160.8 & 86.02 & 1.82 & 2.13 & 76.57 & 2.20 & 1.02 \\
163.2 & 81.45 & 2.28 & 1.10 & 76.70 & 2.47 & 0.82 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Path loss model parameters. Figure 7: (**a**) FI model path loss model parameters; (**b**) CI model path loss model parameters. environment; specifically, outdoor open environments with ground, trees, and smooth tiles will produce abundant reflections, leading to multipath fading. Furthermore, the strong directionality of millimeter wave beams can also create device alignment problems, especially when the distance is set at 200m and more. The 10\({}^{\circ}\) horn antenna with a wide antenna beam used in these measurements also make it harder for antennas to perfectly align. When the distance is greater than a certain value, the signal interferes with ground reflection and direct transmission.