## 2 Materials and Methods
### Duty Cycle Measurement
#### 2.2.2 Single-User DC Measurement  
In the single-user scenario, seven commonly used internet activities were selected based on their distinct traffic patterns, covering streaming, communication, file transfer, gaming, and browsing:  
1. YouTube video streaming: A single video was streamed at two resolutions, 2160p (i.e., so-called 4K video, 4096\(\times\)2160 pixels) and 1080p (1920\(\times\)1080 pixels);
2. WhatsApp communication: Both voice and video calls were conducted;
3. File Transfer Protocol (FTP): File download (DL) and upload (UL) were tested;
4. Online gaming: Overwatch 2 (OW2) was involved;
5. Web browsing: The Edge browser was used to randomly access MSN news (www.msn.com);
6. Audio streaming: Spotify was used for music streaming;
7. Live streaming: Twitch was used to stream video content at 1080p resolution and 30 frames per second (fps).  
To measure DC during these activities, a laptop of Dell Latitude 5430 was used as the UD, featuring an Intel Wi-Fi 6E AX210 WLAN adapter module with an integrated 2\(\times\)2 MIMO antenna embedded in the screen bezel. The experimental setup is shown in Figure 1, where the laptop maintained a line-of-sight (LOS) distance of 5 m from the AP with no obstructions to ensure excellent channel conditions. The three-axis isotropic antenna was positioned at the AP side, with the antenna's center located 35 cm from the AP antenna to satisfy far-field conditions (the diameter of the three-axis antenna radome is 20 cm), as shown in Figure 1b. A section of the Wi-Fi 6 signal recorded in the preliminary experiments with zero-span mode is shown in Figure 2, where three distinct signals can be identified by power density levels: the AP signal, the UD signal, and the noise. For DC estimation using Equation (1), Wi-Fi signals were defined as any signal exceeding the noise floor (-76 dBm) by 5 dB. The active time (\(T_{active}\)) was defined as the duration for which the signal exceeded this threshold. Signals stronger than -60 dBm were attributed to the AP, while remaining signals above the threshold were attributed to the UD. This allowed for the calculation of DC values for both AP and UD transmissions.  
To investigate the impact of varying bandwidths on Wi-Fi 6 DC, the AP bandwidth was sequentially set to 20 MHz, 40 MHz, 80 MHz, and 160 MHz for each internet activity. The corresponding channels and their center frequencies are detailed in Tables 2 and 4, and the SA's center frequency was adjusted accordingly. Each measurement session lasted at least 6 min, consistent with the ICNIRP guidelines for estimating time-averaged exposure levels [6]. During each session, the network applications remained continuously active to ensure representative results. For data post-processing, a single DC sample was calculated for each second of recorded signal, nevertheless, for combining with the exposure values obtained from the max-hold approach to check ICNIRP limits compliance, we advise to use  
\begin{table}
\begin{tabular}{c c c} \hline
**Parameter 1** & **Time Domain** & **Frequency Domain** \\ \hline CF [GHz] & 5.18, 5.23, 5.29, or 5.57 & 5.18, 5.23, 5.29, or 5.57 \\ Span [MHz] & 0 & 40, 60, 100, or 200 \\ RBW [MHz] & 20 & 1 \\ VBW [MHz] & 40 & 10 \\ SWT [ms] & 10 & 6.2 \\ Points & 2401 & 455 \\ Detector & RMS & RMS \\ Trace Mode & Clear/Write & Max-hold \\ \hline \end{tabular} \({}^{\dagger}\) CF = center frequency; RBW = resolution bandwidth; VBW = video bandwidth; SWT = sweep time.  
\end{table}
Table 4: The configuration of the spectrum analyser in time-domain and frequency-domain modes.  
the mean DC during 6 min given in the results, which provides a realistic reflection of the average exposure level in the time period specified by the ICNIRP guidelines. Please bear in mind that the DC measurements in each of the other scenarios presented below were taken over 6 min and post-processed in the same way as the data unless explicitly indicated.