802.11n/ac/ax/be Measurement Capabilities

Option BHJ 802.11n/ac HT high throughput/VHT very high throughput (VHT) physical (PHY) layer protocol data unit (PPDU):A PPDU transmitted using the TXVECTOR FORMAT parameter equal to VHT. modulation analysis and Option BHX (also requires BHJ) 802.11ax HE modulation analysis provides the following MIMO Multiple Input, Multiple Output: A physical layer (PHY) configuration in which both transmitter and receiver use multiple antennas. measurement capabilities:

802.11n/ac/ax/be modulation analysis supported features

802.11n/ac modulation analysis limitations

802.11n/ac HT OFDM modulation analysis exceptions

Direct Mapping Measurement Capabilities

Normally the number of analyzed input channels must equal the number of spatial streams. However there is an exception for signals that use Direct Mapping for the Spatial Mapping matrix. In this special case, any subset of the input channels can be analyzed because each transmitter is essentially independent of the other transmitters. For example, if you have a 4x4 802.11n/ac signal (a 4-transmitter signal that has 4 spatial streams) that use Direct Mapping, then you can measure the signal from any one of the transmitters and successfully analyze it, or you can measure the signals from any two or any three of the transmitters and successfully analyze them.

STBC Analysis Capabilities

STBC signal analysis is not specifically supported by the 802.11n/ac demodulator. However there is an exception for STBC signals that use Direct Mapping for the Spatial Mapping matrix. In this special case, it is possible to demodulate one or more transmit channels independently, and even a single transmit channel can be analyzed by itself, since each channel is essentially independent of the others when Direct Mapping is used.

802.11n

It may be possible to analyze two or three transmitters of a Direct Mapped STBC signal depending on the values of the MCS modulation and coding scheme and STBC fields in the HT-SIG part of the signal. The MCS and STBC measurement values are located in the OFDM SIG Info trace. These data results should normally be available even when the rest of the demodulation is unsuccessful.

Using the MCS and STBC values, identify which pairs of transmitters encode a single spatial stream (e.g., 1 and 2, or 3 and 4). Connect the VSA inputs to one transmit channel from each encoded pair, and connect the VSA to the other the non-encoded transmit channels. This will provide the VSA with a square (2x2 or 3x3) MIMO signal, which can then be demodulated as if there were no STBC applied.

802.11n (see Table 20.18 in the 802.11n standard for STBC constellation mapping information)
MCS STBC

Channels to analyze

  

Spatial Streams

 MIMO config

Encoded

TX Transmit or transmitter Pairs

2 Ch HW

3+ Ch HW
0-7 1 Select single channel: (1 or 2) 1 2x1 1&2
8-15, 33-38 1 Select two: (1 or 2), 3 2 3x2 1&2
8-15 2 Select two: (1 or 2), (3 or 4) 2 4x2 1&2, 3&4
16-23 1

Select two:

(1 or 2), 3, 4

Select three:

(1 or 2), 3, 4

 3 4x3 1&2
39, 41, 43, 46, 48, 50 1

Select two:

(1 or 2), 3, 4

Select three:

(1 or 2), 3, 4

 3 4x3 1&2

802.11ac

The variations of STBC are simpler in 802.11ac. Encoded TX pairs are always odd/even. For instance, a 6-channel STBC signal has three spatial streams and the encoded TX pairs are channels (1,2), (3,4), and (5,6). This means you could connect channels {1,3,5} or channels {2,4,6} to the VSA and demodulate this 6-channel Direct Mapped STBC 802.11ac signal.

See Table 22.20 in the P802.11ac draft standard for STBC constellation mapping information.

See Also

Selecting 802.11n/ac/ax/be HT OFDM Demodulation

Using a Standard Setup

Troubleshooting (802.11n/ac/ax/be)