The unused tone error test is an additional modulation accuracy (ModAcc) test for the unoccupied subcarriers in a HE or EHT TB PPDU, as defined in section 27.3.18.4.4 of IEEE P802.11ax/D8.0 or section 36.3.20.4.4 of IEEE Standard P802.11be/D7.0, respectively. You calculate the unused tone error for each unused 26-tone resource unit (RU) by averaging across 26 subcarriers and normalizing the value with the average power in the occupied subcarriers.

For example, the RU index for 20 MHz TB PPDU ranges from 0 to 8, with 0 being the left most 26-tone RU and 8 being the right most 26-tone RU in the frequency axis. The unused tone error mask, with respect to the RU index, is the standard specified maximum limit for unused tone error as defined by the following equations.

where

  • iRU26,start is equal to the occupied RU index if the occupied RU is a 26-tone RU. For more information on this index, see Table 27-50 of IEEE P802.11ax/D8.0 and Table 36-66 of IEEE P802.11be/D7.0 for other RU sizes.
  • r is the occupied RU bandwidth in units of a 26-tone RU.
  • iRU26,end is equal to iRU26,start + r − 1.
  • m defines the gap in the units of the 26-tone RU to the occupied RU. m is an integer with m = ±1 being the adjacent 26-tone RUs.
  • ε is the relative constellation error for the HE TB PPDU defined in table 27-49 of IEEE P802.11ax/D8.0 and Table 36-65 of IEEE P802.11be/D7.0.

The standard specifies two limits for UsedToneError. If the transmit power is less than or equal to the maximum power of MCS7, a tighter mask is applied on the unused tone error. Subsequently, if the transmit power is more than maximum power of MCS7, a relaxed mask is applied.

In case of a non-contiguous multiple RU (MRU), the transmit modulation accuracy test for the unoccupied subcarriers of the PPDU is performed by constructing the overall relative constellation error staircase mask as following.

  1. Treat the non-contiguous MRU as a large RU/MRU that does not have an unmodulated portion in between multiple RUs. For example, 2 x 996 + 484-tone MRU is treated as 3 x 996-tone MRU
  2. Find the average unused subcarrier error vector magnitude for each unoccupied 26-tone RU based on the large RU/MRU.
  3. Replace the unmodulated portion in between multiple RUs to max (ε – 2, – 38) dB.

The following figure is a graphical representation of the unused tone error measurement for a 20 MHz 802.11ax TB PPDU with a 52-tone RU at offset 5.

where

  • [m0,...,mn]: Unused Tone Error Margin Vector (dB)
  • mmin: Unused Tone Error Margin (dB)
  • imin: Unused Tone Error Margin RU Index