OFDM Multi-User Info (802.11n/ac/ax/be)

OFDM Multi-User Info is a table with information about all the users detected in the burst (from the data in the Measurement Interval).

In an 802.11ac signal, there can be up to N_ss=N_t spatial streams, where N_t is the number of transmit channels. There can also be up to 4 users per burst with up to 4 streams allocated to each user. For example, in a 3 user, 6 channel signal, the stream allocations could be (S1, S2) => user 0, S3 => user 1, and (S4, S5, S6) => user 2.

The following information is listed for each user:

EVM(dB) - error vector magnitude, averaged over all subcarriers, symbols, and streams for the user
MCS - Modulation and Coding Scheme index
ModFmt - modulation format.

The OFDM Orthogonal Frequency Division Multiplexing: OFDM employs multiple overlapping radio frequency carriers, each operating at a carefully chosen frequency that is Orthogonal to the others, to produce a transmission scheme that supports higher bit rates due to parallel channel operation. OFDM is an alternative tranmission scheme to DSSS and FHSS. Multi-User Info trace provides VHT very high throughput (VHT) physical (PHY) layer protocol data unit (PPDU):A PPDU transmitted using the TXVECTOR FORMAT parameter equal to VHT.-SIG-B or HE-SIG-B decoded user specific info. Trigger-Based burst is a special uplink burst with multiple RUs but no SIG-B preambles. When Trigger-Based HE PPDU RU Allocation is used, MCS modulation and coding scheme and ModFmt (derived from MCS) use default values and "***" is shown in the ModFmt data column.
Streams - number of streams used
Len(4octet) - (802.11n/ac only) length of user data in number of 4-byte words as indicated by the Length field in VHT-SIG-B symbol for the user
Pwr(dBm) - absolute power for a user, averaged over input channels

This metric is calculated for a user by the following steps:
1. Demodulate 802.11ac signal and get all users data
2. Set other user's data to zero
3. Create reference signal for each Tx antenna
4. Calculate the average power over all Tx antennas
STA-ID - (802.11ax/be only) the STA Station: Any device that contains an IEEE 802.11 conformant medium access control (MAC) and physical layer (PHY) interface to the wirless medium (WM).-ID value for each user (decoded from HE SIG-B user specific part and described in 9.4.1.8 of the 802.11ax specification, or from EHT-SIG user specific part and described in 36.3.11.8.5 of the 802.11be specification).
DCM - (802.11ax/be only) indicates whether or not the payload of the HE/EHT MU Multi-user PPDU PLCP Protocol data unit is modulated with dual-carrier modulation (decoded from HE SIG-B/EHT-SIG user specific part)
Coding - (802.11ax/be only) indicates whether the BCC binary convolutional code or LDPC low-density parity check coding type is used (decoded from HE SIG-B/EHT-SIG user specific part)
TxBF - (802.11ax/be only) indicates whether or not transmit beamforming is used (decoded from HE SIG-B/EHT-SIG user specific part)
CRC - (802.11ax/be only) pass/fail value from the CRC Cyclic Redundancy Check of the decoded PSDU 1) PHY Service Data Unit, or 2) PLCP SDU. A “P” means the CRC passes, while a “Fail” means the CRC failed. This column is enabled only if the Decode PSDU and Verify CRCs checkbox on the Advanced Tab is checked. If this checkbox is not checked, the column will show a “***" value. PSDU decoded bits are displayed in the PSDU Decoded Bits trace.
GainImb(dB) - (802.11ax/be only) indicates the IQ Gain Imbalance for each user in the table. This column is enabled only if the Estimate IQ Mismatch Per Subcarrier checkbox on the Advanced Tab is checked. If this checkbox is not checked, the column will show a “***" value.
QuadErr(deg) - (802.11ax/be only) indicates the IQ Quadrature Error for each user in the table. This column is enabled only if the Estimate IQ Mismatch Per Subcarrier checkbox on the Advanced Tab is checked. If this checkbox is not checked, the column will show a “***" value.