Increasing number of nodes in OFDMA

I am working on "802.11ax Downlink Throughput Comparison of OFDM and OFDMA Through System-level Simulation" codebase using command "openExample('wlan/Downlink80211axOFDMAExample')". When I increase the number of client nodes to nine, it is working fine for OFDM but for OFDMA it is generating exception as below:

"

• Discrete-event system 'phyRx' for 'Downlink80211axOFDMAModel/Station-1/PHY Receiver/rxBlock' error occurred when invoking 'waveformTimer' method. The error was thrown from ' 'C:\Program Files\MATLAB\R2021a\toolbox\wlan\wlan\wlanHERecoveryConfig.m' at line 1019 'C:\Program Files\MATLAB\R2021a\toolbox\wlan\wlan\wlanHERecoveryConfig.m' at line 881 'C:\Program Files\MATLAB\R2021a\toolbox\wlan\wlan\wlanFieldIndices.m' at line 639 'C:\Program Files\MATLAB\R2021a\toolbox\wlan\wlan\wlanFieldIndices.m' at line 113 'C:\Users\jagra\OneDrive\Documents\MATLAB\Examples\R2021a\wlan\Downlink80211axOFDMAExample\phyRx.m' at line 379 'C:\Users\jagra\OneDrive\Documents\MATLAB\Examples\R2021a\wlan\Downlink80211axOFDMAExample\phyRx.m' at line 608 'C:\Users\jagra\OneDrive\Documents\MATLAB\Examples\R2021a\wlan\Downlink80211axOFDMAExample\phyRx.m' at line 875'.
• The RXTIME must be greater than or equal to the preamble duration of the packet in microseconds. "

Can you please help me as to how I can resolve this issue. Moreover, please tell me how can I increase the number of client nodes to more than 9.

Thanks

Answer 1

[Umeshraja]

Hi @Jagrati Kulshrestha,

The error you're encountering typically arises when the MCS is set too high. Try reducing the MCS to lower values to avoid this issue. Additionally, ensure that the packet size in the Application Traffic Generator is set to a nominal value and not too large. Given that this example uses a 20MHz bandwidth, the allocation of Resource Units (RUs) to downlink stations is fixed based on the number of users, as shown in the table provided in the "Further Exploration" section of the example.

In a 20MHz OFDMA transmission, a maximum of 9 users can be supported with 26-tone RUs. Therefore, if you try to add more than 9 client nodes, there will be no resource units available for additional transmissions.

Hope it helps!