# SDR-Enabled Multichannel Real-Time Measurement System for In Situ EMF Exposure Evaluation
## 3 Results
### Comparative Performances of the Measurement Instruments
Table 2 presents the comparative analysis of the measurement system based on their hardware and software requirements, flexibility, cost, and investigated performance. The criteria were selected based on their suitability for in situ measurements of EMF emitted in the vicinity of present-day RF communication devices. One should keep in mind that SDR instruments cannot be considered as reliable and accurate as traditional measurement instrumentation. As can be observed in Figure 11, SA measurement systems present the highest performances in terms of the displayed average noise level (DANL) and accuracy. However, to perform synchronous multichannel measurements, we need a significant number of measurement instruments (three in the presented scenario if SA are to be used). This results in excessive costs, reduced mobility, and scarce flexibility. These issues make such a measurement system unsuitable for in situ measurements, near an emitting device in various operating environments. The recent technological development of DOs made it possible for these instruments to be used for frequency domain measurements also. We have studied the suitability of using a high performance DO for synchronized multichannel RF measurements. The current capabilities of the DO enables CP measurements for frequencies lower than the maximum available oscilloscope bandwidth. The limitations imposed by the DO-enabled measurement system relate to the instrument response time, the maximum available sample \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Criteria**} & \multicolumn{2}{c}{**SDR-Enabled**} & \multicolumn{2}{c}{**SA-Enabled**} & \multicolumn{2}{c}{**DO-Enabled**} \\  & **Measurement System** & & **Measurement System** & & **Measurement System** \\ \hline \multirow{8}{*}{Hardware requirements} & \(\bullet\) & E-field sensor & \(\bullet\) & E-field sensor & \(\bullet\) & E-field sensor \\  & \(\bullet\) & E-field sensor & \(\bullet\) & \(3\times\) SAs & \(\bullet\) & \(1\times\) DOs \\  & \(\bullet\) & \(1\times\) USRPs & \(\bullet\) & \(3\times\) Computers for & \(\bullet\) & Computer for remote \\  & \(\bullet\) & Computer with fiber & & remote control & & control measurements \\  & & optic network card for & & measurements & \(\bullet\) & External signal source \\  & & 10 GB link with USRP & \(\bullet\) & External signal source & \(\bullet\) & External signal source for triggering \\ \hline \multirow{2}{*}{Software requirements} & GNU Radio (open source) & Python application for & Python application for remote control process & Python application for remote control process \\ \hline \multirow{2}{*}{Flexibility} & Medium & Reduced & Medium & \\ \hline \multirow{2}{*}{Performance} & DANL & Good & Good & Best \\  & & Good, can be improved if & & Good but limited to sub 4 GHz \\ \multirow{2}{*}{Accuracy} & Good, previously calibrated & \multirow{2}{*}{High} & Good but limited to sub 4 GHz & frequency range \\ \hline \multirow{2}{*}{Cost (Euro)} & \multirow{2}{*}{17,000} & \multirow{2}{*}{63,500} & \multirow{2}{*}{33,500} \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparative analysis of the measurement systems. Figure 12: SDR calibration results in 3.3–3.7 GHz frequency band (**left**) and 5–5.9 GHz frequency band (**right**). rate, and the bandwidth. At the current technological development these limitations are often insufficient, especially for higher frequency applications. Therefore, the SDR receiver has several advantages in terms of hardware and software requirements, cost, and flexibility. In addition, we obtained similar performances of the SDR-enabled measurement system as compared to the traditional approaches considered. Even so, the use of the SDR implies other problems that need careful solving. These problems refer mainly to the calibration of the amplitude response, for which we have used a simplified but effective procedure.