## 3 Measurement Setup
### Data Analysis Method  
We used the recorded data with the channel sounder to create the PDP. The PDP contains one bin per 65 ns of delay. The I/Q data were stored in the HDD every 0.5 s. A single PDP is calculated from the correlation between the pre-defined PN sequence and one 0.5 s I/Q data. A set of PDPs composes one PDP set, which represents a single measurement. From the PDP, we evaluated the propagation channel characteristics, such as the path loss exponent, Ricean K-factor, and the Doppler spread, which were obtained from the post-processing of the recorded data. The Ricean K-factor describes the rate between the signal powers of the line-of-sight (LoS) or dominant path and the reflected paths as Equation (1). We considered the spec \begin{table}
\begin{tabular}{c c l} \hline \hline  & \multicolumn{1}{c}{**Component**} & \multicolumn{1}{c}{**Specification**} \\ \hline \multicolumn{2}{c}{Software Platform} & \multicolumn{1}{c}{GNU Radio} \\  & Amplifier & \begin{tabular}{c} Ophir (Los Angeles, CA, USA) \\ \end{tabular} & \begin{tabular}{c} 5304043/50 dB Gain \\ Pasterrack (Irvine, CA, USA) \\ \end{tabular} & \begin{tabular}{c} 5304043/50 dB Gain \\ Isolator \\ \end{tabular} \\ \multirow{2}{*}{Transmitter} & \multirow{2}{*}{Antenna} & \begin{tabular}{c} Mobile Mark (Itasca, IL, USA) EC012-5900 \\ 12 dBi omnidirectional antenna \\ \end{tabular} \\  & \begin{tabular}{c} Transmission Power \\ Amplifier \\ \end{tabular} & \begin{tabular}{c} 10 dBm \\ Miteq (Hauppauge, NY, USA) AFS3 0010100-20-10P-4 \\ 0.1–10 GHz 30 dB Gain \\ \end{tabular} \\  & \begin{tabular}{c} (1) \\ 12 dBi omnidirectional antenna \\ \end{tabular} \\ \multirow{2}{*}{Receiver} & \multirow{2}{*}{Antenna} & \
\begin{tabular}{c} Mobile Mark EC012-5900 \\ 12 dBi omnidirectional antenna \\ \end{tabular} \\  &
\begin{tabular}{c} Antenna \\ 23 dBi bidirectional antenna \\ \end{tabular} \\ \multirow{2}{*}{Receive Noise Figure} & \textless{}8 dB \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Channel sounder transmitter and receiver component specifications. Figure 1: Channel sounder transmitter and receiver (**a**) diagram, (**b**) implementation. ular power as the dominant signal power and the non-specular power as the reflected signal power in the PDP. The Ricean K-factor for a specific index can be calculated using Equation (1) for each PDP index:  
\[\mathrm{K}=\frac{\mathrm{Specular\ Power}}{\mathrm{Nonspecular\ Power}} \tag{1}\]  
We calculated the Doppler spread (Hz), RMS delay spread (\(\tau_{\mathrm{rms}}\)), and the path loss exponent (n) by evaluating the comparison between the LoS and the multipath signals. The Doppler spread is directly obtained from the Matlab function 'pwelch'. We set the Doppler spread as the frequency when the result of 'pwelch' was the maximum. The RMS delay spread defines how much the channel's average delay spread was captured in the specific measurement. The RMS delay spread was calculated as the square root of the second central moment of the PDP as Equation (2). The second central moment can be obtained by Equations (3) and (4):  
\[\tau_{\mathrm{rms}}=\sqrt{\overline{\tau^{2}}-\ \overline{\tau}^{2}} \tag{2}\]  
\[\overline{\tau^{2}}=\frac{\sum\mathrm{P(\tau_{i})\tau_{i}}^{2}}{\sum\mathrm{P( \tau_{i})}} \tag{3}\]  
\[\overline{\tau}=\frac{\sum\mathrm{P(\tau_{i})\tau_{i}}}{\sum\mathrm{P(\tau_{i} )}} \tag{4}\]  
The path loss exponent is the rate of the received signal strength decreasing with distance. The path loss exponent (n) can be calculated using Equation (5). \(\mathrm{P_{t}}\) represents the transmission power; \(\mathrm{P_{r}}\) represents the received power; \(\mathrm{d}\) represents the distance between the transmitter and the receiver; and \(\mathrm{K_{0}}\) is the free-space path loss, which can be described using Equation (6):  
\[\mathrm{n}=\frac{-\left(\mathrm{P_{t}}-\mathrm{P_{r}}+10\log_{10}\mathrm{K_{0} }\right)}{10\log_{10}\mathrm{d}} \tag{5}\]  
\[\mathrm{K_{0}}=20\log_{10}\frac{4\pi}{\lambda} \tag{6}\]  
The post-processing was performed by Matlab script.