Orthogonal Frequency Division Multiple Access (OFDMA) is a multi-user version of the popular Orthogonal Frequency Division Multiplexing (OFDM) digital modulation scheme. Multiple access is achieved in OFDMA by assigning subsets of subcarriers to individual users. This allows simultaneous data transmission to and from several users.

802.11ax systems require close Access Point (AP) to station “handshaking.” Think of the AP as a mini base station. The AP groups transmissions for download and upload and to and from multiple users. This requires precise timing and frequency control to combine multiple users together.

The OFDMA system supports users to “talk” at the same time (<400 ns difference) and at the same carrier frequency (<350 Hz difference). In addition, the AP talks “loud” (higher power) to far away users and “soft” (lower power) to close users. Additionally, users that are far away need to talk “louder” to the AP and users that are close need to talk “softer” to the AP. Each user is allocated one or more Resource Units (RU). Resource Units are segments of time and frequency similar to today’s cellular technology.

Why does that matter? Testing time and frequency creates many more scenarios that need to be tested with critical accuracy compared with traditional Wi-Fi. Test calibration is also required for power level source and measurement.