# Real-Time Statistical Measurement of Wideband Signals Based on Software Defined Radio Technology
## 3 Materials and Methods
### Parameterization and Test System Implementation  
In order for the proposed system to correctly measure all the parameters implemented in the software, it is necessary to use the reference system to adjust them. This process is called parameterization. In this case, parameterization of the software refers to the fact that the software is adapted to the desired range of functions by setting parameters in relation to the results displayed by the reference system. For this purpose, the Rohde and Schwarz SMM100A signal generator was connected to one of the two RX channels of the USRP platform via a coaxial cable. The USRP device was also connected to the PC via fiber optic cable, where the application implemented in GNU Radio was running (Figure 7). The test signals were verified by comparison with the Rohde and Schwarz FSVR7 real-time SA (frequency range 10 Hz-7 GHz). The R&S SMM100A vector signal generator equipped with the SMM-K142 for the IEEE802.11 ax standard was used for signal generation. Parameterization was performed for a downlink channel with a bandwidth of 40 MHz (the bandwidth was selected for comparison with the SA, which is limited to 40 MHz real-time acquisition). The other set of parameters that define the 802.11 ax standard are highlighted in Table 2 and Figure 8. To determine the correct parameters for the SDR system, comparative measurements were performed. \begin{table}
\begin{tabular}{l l} \hline Link direction & Downlink \\ Physical Layer Protocol Data Unit (PPDU) & HE SU (transmitting to a single user) \\ Bandwidth & 40 MHz \\ Symbol duration & 12.8 \(\upmu\)s \\ Guard interval duration & 3.2 \(\upmu\)s \\ Aggregate MAC Protocol Data Unit (A-MPDU) length & 1028 bytes \\ Modulation schemes & 1024 QAM (25\% higher capacity than 802.11 ac) \\ Data rate & 286.76 Mbps \\ Bits per symbol & 3900 \\ Generated power level & \(-\)30 dBm \\ \hline \end{tabular}
\end{table} 
Table 2: Description of the generated 802.11 ax signal. Figure 7: Experimental test setup for setting parameters. Laboratory testing ensures correct signal processing, which is achieved when the signals transmitted by the generator match in display value after the signal passes through the SDR platform. The \"Multiply\" block was used to set the parameters. In the first step, after setting the correction parameters, the amplitude response of the SDR system was performed for the same test signal (described in Table 2), but for a dynamic range of the input signal level between \(-30\) dBm and \(-70\) dBm. Comparative measurement results between the SDR platform and the reference spectrum analyzer are shown in Table 3. It can be seen that the SDR platform has a good response to the dynamic range of the channel power being analyzed, with results comparable to those of the spectrum analyzer, the differences being less than \(1\) dBm. Under the same laboratory conditions (with the exception of the bandwidth variation), the channel noise power was also analyzed by sequentially connecting a \(50\) ohms impedance to both the RF input of the SDR platform and the reference SA. The measurement results are shown in Table 4. We are interested in this parameter because the channel noise will have an impact on the minimum power level, we can measure at a given time. The results obtained show a difference of approximately \(3\) dB between the SDR system and the reference SA. This means that the SDR platform is at least \(3\) dB less sensitive than the reference SA in its ability to measure low-level signals. The second step was to generate signals specific to the IEEE 802.11 ax standard, for CP measurements and statistical measurements CCDF, to see the efficiency of the SDR \begin{table}
\begin{tabular}{c c c c c} \hline \hline Channel Bandwidth [MHz] & \(20\) & \(40\) & \(80\) & \(160\) \\ \hline Channel Power Noise measured with R\&S FSVR7 [dBm] & \(-79.95\) & \(-76.78\) & - & - \\ \hline Channel Power Noise measured with USRP X310 [dBm] & \(-76.7\) & \(-73.6\) & \(-70.2\) & \(-67.7\) \\ \hline \hline \end{tabular}
\end{table}