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 supported features
- 802.11n/ac modulation analysis limitations
- 802.11n/ac modulation analysis exceptions
802.11n/ac/ax/be modulation analysis supported features
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Guard Interval support for standard and user specified guard interval time.
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Supports 20 MHz Megahertz: A unit of frequency equal to one million hertz or cycles per second. and 40 MHz bandwidth signals for 802.11n/ac/ax, 80 MHz, 80+80 MHz and 160 MHz for 802.11ac/ax, and 320 MHz for 802.11be. The bandwidth of the test signal must be manually specified.
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Automatically detects and analyzes Non-HT, HT-mixed, HT-greenfield, and VHT 802.11n/ac formatted signals as well as HE/EHT 802.11ax/be.
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Automatically analyzes 802.11n/ac signals that contain extra HT-LTF Long Training field symbols (VSA ignores extra symbols).
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Automatically determines the subcarrier modulation format.
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Automatically determines the burst length.
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The VSA correctly decodes the EHT-SIG, VHT-SIG, HT-SIG High-Throughput SIGNAL field and L-SIG Non-HT SIGNAL field symbols for cases when the STBC Space–Time Block Coding is a alternative to spactial multiplexing used in wireless communications to transmit multiple copies of a data stream across a number of antennas. Particularly useful for systems where the number of receive antennas is less than the number of transmit antennas.and to exploit the various received versions of the data to improve the reliability of data-transfer. is used for the data part of the burst or the number of spatial streams in the data part of the burst does not match the number of input channels. The trace shows the information from the EHT-SIG, VHT-SIG, HT-SIG and L-SIG symbols.
802.11n/ac modulation analysis limitations
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VSA does not support STBC signal analysis with the following exception, STBC signals that use Direct Mapped Spatial Streams.
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802.11n/ac modulation analysis does not support Non-HT (legacy) signal measurements; to analyze a pure 802.11n/ac legacy signal, use the Wireless Networking 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. modulation analysis mode for 802.11a/b/g/j signals. In 802.11n/ac demod mode, a pure legacy signal will demodulate, but there will be a SYNC NOT FOUND trace indicator and the data in the is blanked out. If you click on the SYNC NOT FOUND trace indicator, it will state "802.11a Legacy Mode signal not supported in 802.11n/ac measurement."
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.
MCS | STBC |
Channels to analyze |
Spatial Streams |
MIMO config |
Encoded |
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2 Ch HW |
3+ Ch HW |
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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
Troubleshooting (802.11n/ac/ax/be)