## 4 Methodology and Setup
### Evaluation Methodology  
To evaluate the interference robustness of the SUN-OFDM PHY and compare it to the OQPSK-DSSS PHY, we use the setup depicted in Figure 3. The setup consists of a transmitter, a receiver and an interferer device connected through an RF (RadioFrequency) power combiner (further described in Section 4.3). For the SUN-OFDM modulation, we select the operating modes that provide a similar data-rate of the OQPSK-DSSS mode, 250 kbps. In particular, we select the OFDM1-MCS1, OFDM2-MCS2, OFDM3-MCS3 and OFDM4-MCS5 modes that provide a data-rate of 200 kbps but with different PHY properties (i.e., channel bandwidth, modulation, coding rate and frequency repetition) as presented in Section 2 and summarized in Table 2.  
For the measurement campaign, each selected modulation is used as an interferer signal, and tested against all other selected modulations acting as transmitter signals (OFDM1-MCS1, OFDM2-MCS2, OFDM3-MCS3, OFDM4-MCS5, OQPSK-DSSS). The procedure is also repeated for two different payload lengths (20 bytes and 120 bytes) in order to understand the effects of packet length on the robustness of each modulation. This is relevant as the SUN-OFDM modulation adds symbol redundancy in both time and frequency, whereas OQPSK-DSSS only adds redundancy in terms of the spreading factor gain. In addition, each base experiment is repeated twice for each transmitter and interferer device (i.e., exchanging the devices' roles). We use this approach to verify the obtained results and cancel out possible differences in the transmit power between the devices (due to the radio transceiver construction variability and/or the impedance matching of the RF circuit) that may affect the obtained results. Overall, this gives a total of 10 base experiments, one for each interferer signal and payload length, as presented in Section 5. Each base experiment uses a particular modulation as interferer, and evaluates the robustness of all the modulations being tested in the measurement campaign, including itself. For instance, OFDM1-MCS1 is selected as interferer and tested against OFDM1-MCS1, OFDM2-MCS2, OFDM3-MCS3, OFDM4-MCS5 and OQPSK-DSSS. To ensure that noise and external interference do not affect the results, we set the transmit power to a value that is well above the sensitivity limit of the radio transceiver for each modulation \begin{table}
\begin{tabular}{p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt}} \hline \hline
**Name** & **Mode** & **Modulation** & \begin{tabular}{c} **Channel** \\ **Coding** \\ \end{tabular} & \begin{tabular}{c} **Frequency** \\ **Repetition** \\ \end{tabular} & \begin{tabular}{c} **Receiver** \\ **Sensitivity** \\ **(dBm)** \\ \end{tabular} & \begin{tabular}{c} **Effective** \\ **Data-Rate** \\ **(kbps)** \\ \end{tabular} & \begin{tabular}{c} **Channel** \\ **Bandwidth** \\ **(kHz)** \\ \end{tabular} & **Abbreviation** \\ \hline \begin{tabular}{c} OQPSK- \\ DSSS \\ \end{tabular} & \(\mathrm{N/A}\) & OQPSK & \(\mathrm{N/A}\) & \(\mathrm{N/A}\) & \(-103\) & \(250\) & \(5000\) & OQPSK-DSSS \\ \hline \begin{tabular}{c} OFDM \\ Option 1 \\ \end{tabular} & MCS1 & BPSK & \(1/2\) & \(2\)x & \(-109\) & \(200\) & \(1200\) & OFDM1-MCS1 \\ \hline \begin{tabular}{c} OFDM \\ Option 2 \\ \end{tabular} & MCS2 & QPSK & \(1/2\) & \(2\)x & \(-108\) & \(200\) & \(800\) & OFDM2-MCS2 \\ \hline \
\begin{tabular}{c} OFDM \\ Option 3 \\ \end{tabular} & MCS3 & QPSK & \(1/2\) & \(0\)x & \(-107\) & \(200\) & \(400\) & OFDM3-MCS3 \\ \hline
\begin{tabular}{c} OFDM \\ Option 4 \\ \end{tabular} & MCS5 & \(16\)-QAM & \(1/2\) & \(0\)x & \(-105\) & \(200\) & \(200\) & OFDM4-MCS5 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: IEEE 802.15.4-2015 modulations that have been selected in this study to evaluate their robustness against interference. Figure 3: Evaluation setup. Note that the grey box around the transmitter, interferer and receiver devices represents an RF shielding enclosure used to ensure that communication between devices can only occur through the RF coaxial cables.