## 6 Discussion and Conclusions  
This study discusses an extensive measurement campaign that was carried out in a pedestrian tunnel, in which various parameters were measured, including the delay spread. The results of the measurements obtained were processed to show their enormous significance in characterizing the limitations of wireless communication in tunnels. The main feature of pedestrian tunnels is the fact that they are narrow and long in relation to  
Figure 10: RMS delay spread comparison between the experiment and simulation.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Symbol** & **Experiment** & **Simulation** \\ \hline Spread Delay (ns) & \(\sigma_{\tau}\) & 0.55 & 0.54 \\ \hline \hline \end{tabular}
\end{table}
Table 8: Summary Results.  
their width and height. This unique characteristic affects the arrival time of the LOS ray in comparison to the time of arrival of the rays reflecting off the walls.  
Using our theory, as described in Section 2, an analysis was made of the received power and the delays in the arrival of the signal at the receiver as a result of the distance between the transmitter and the receiver. To validate the model, a wide-band experiment was performed using a VNA, which provided us with high-resolution measurements. With the use of optical means, the ability to receive the signal accurately was achieved. The results were presented, in Section 4, in the form of a comparison with the results of the theory, and as can be observed there is an excellent fit.  
One of the main characteristics of the pedestrian tunnel is that the RMS delay spread, \(\sigma_{\tau}\), decreases along the tunnel. This can be explained by the fact that as the distance increases the rays returning from the walls have a lower power due to the attenuation created by the reflections from the wall. This is in contrast to the direct LOS ray, with the only effect on it being free space loss, which is lower. The sizes obtained, mean and RMS delay spread are of the same order of magnitude as the results obtained in previous studies that were performed in areas with similar topography. In contrast to the previous studies, this research is the most in-depth and comprehensive study of communication limitations in the pedestrian tunnel.  
As was presented, there is a process of dispersion within the tunnel that is affected by Multi path, the effect of the dispersion on the communication channel may cause inter-symbol interference and should be considered in channel design.  
Conceptualization, Y.T., Y.P. and L.R.; methodology, Y.T. and Y.P.; software, Y.T., L.R. and G.A.P.; validation, Y.P.; formal analysis, Y.T.; investigation, Y.T., L.R. and Y.P.; resources, Y.T., L.R., N.E. and G.A.P.; data curation, Y.T. and N.E.; writing, original draft preparation, Y.T.; writing, review and editing, Y.T.; visualization, Y.T. and Y.P.; supervision, Y.P.; project administration, Y.P.; funding acquisition, Y.P. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
The first and third authors, [PERSON] and [PERSON] would like to thank the Department of Advanced Studies of Ariel University for the scholarship and help. Also, this paper is part of [PERSON]'s PhD thesis and [PERSON] PhD thesis.  
The authors declare no conflict of interest.