HE MU Transmission
Transmission Mode Options
The options for high-efficiency multi-user (HE MU) transmissions are:
Orthogonal frequency-division multiple access (OFDMA)
Full-band multi-user multiple-input/multiple-output (MU-MIMO)
Mixed OFDMA and MU-MIMO
To choose a transmission mode, you must enable or disable SIGB compression by specifying the state of the SIGB compression bit in the HE-SIG-A field.
For a 20 MHz transmission, specify the SIGB compression bit directly by setting the
SIGBCompressionproperty of the
To enable SIGB compression, set the
To disable SIGB compression, set the
For a 40, 80, or 160 MHz transmission, enable or disable SIGB compression by setting the
AllocationIndexproperty of the
When SIGB compression is enabled, the transmission is full-bandwidth MU-MIMO. The HE-SIG-B field contains no common field, and the resource unit (RU) allocation in the user fields adheres to a standard-specified pattern. Because there is no common field in this case, no allocation index is transmitted. The number of users is determined by decoding the HE-SIG-A field.
When SIGB compression is disabled:
The transmission is either OFDMA or mixed OFDMA and MU-MIMO, depending on the
AllocationIndexproperty of the HE MU configuration object.
The HE-SIG-B common field includes RU allocation subfields to specify the RU assignment and the number of users per RU for each 20 MHz bandwidth segment.
The 802.11ax Waveform Generation example introduces the concepts associated with HE transmission modes, RU allocation, and parameterization.
The Recovery Procedure for an 802.11ax Packet example demonstrates the required steps to detect and decode an HE MU transmission.
When creating a
you must specify the value of the
AllocationIndex property. Once the
object is created, the
AllocationIndex property is read-only.
AllocationIndex property defines the RU allocation index or a set
of RU allocation indices.
Specify a single allocation index using one integer in either of these forms.
An integer in the interval [0, 223]
An 8-bit binary sequence specified as a string or character vector
Specify multiple allocation indices using two, four, or eight integer values in any of these forms.
A vector of integers in the interval [0, 223]
An 8-bit binary sequence specified as a string array
An 8-bit binary sequence specified as a cell array of character vectors
You can signal punctured 20 MHz or 40 MHz subchannels in an 80 MHz or 160 MHz transmission. To signal a punctured 20 MHz subchannel, set the corresponding element to
113. To signal a punctured 40 MHz subchannel, set the two corresponding adjacent elements to
114. To signal an empty HE-SIG-B user field in an HE-SIG-B content channel, set the corresponding element to
An RU is a group of 26, 52, 106, 242, 484, 996, or 2×996 subcarriers defining an allocation unit in time and frequency.
The values specified in the
AllocationIndex property correspond to
the 8-bit indices for each 20 MHz subchannel in the first column of Table 27-26 in . The
allocation indices define the number of RUs, RU sizes, and number of users assigned to
each RU. When SIGB compression is enabled, the number of users is determined by decoding
the HE-SIG-A field. When SIGB compression is disabled, the number of users is determined
by decoding the HE-SIG-B common field.
When SIGB compression is enabled, the HE-SIG-B field contains only the user field.
When SIGB compression is disabled, the HE-SIG-B field includes both the common and user fields. The common field carries the RU Allocation subfields in one or two content channels. Depending on the PPDU bandwidth, the common field can contain multiple RU Allocation subfields. For a discussion of the frequency-domain mapping of channel contents into the common field, see section 188.8.131.52.5 of .
This figure shows the structure of the HE-SIG-B field when SIGB compression is disabled.
The format of the common field is defined in Table 27-24 of . The RU Allocation subfield in the common field of HE-SIG-B consists of eight bits that indicate this information for each 20 MHz PPDU bandwidth.
RU assignment in the frequency domain, which determines the size of the RUs and their placement in the frequency domain.
Number of user fields in a 20 MHz band within the HE-SIG-B content channel, which determines the number of users multiplexed in the RUs. For RUs of size greater than or equal to 106 tones, which support MU-MIMO, the RU Allocation subfield indicates the number of users multiplexed using MU-MIMO. The HE-SIG-B field consists of N RU Allocation subfields, where:
N = 1 for 20 MHz and 40 MHz HE MU PPDUs
N = 2 for 80 MHz HE MU PPDUs
N = 4 for 160 MHz and 80+80 MHz HE MU PPDUs
This table lists the allocation indices and corresponding RU assignments for 20 MHz subchannels and RUs with at most 242 tones. The table shows the number of tones per RU and the number of users assigned for each allocation index.
This table lists the allocation indices and corresponding RU assignments for subchannels greater than 20 MHz and RUs of more than 242 tones.
The format of the user field for non-MU-MIMO and MU-MIMO allocations are defined in Tables 27-28 and 27-29, of , respectively.
This table shows allocation index options required to specify transmission type for all channel bandwidths.
|Transmission Type||20 MHz Transmission||40 MHz Transmission||80 MHz Transmission||160 MHz Transmission|
|Full bandwidth MU-MIMO|
|Mixed OFDMA and MU-MIMO|
|20 MHz transmissions have only one content channel.||The |
 IEEE Std 802.11ax™-2021 (Amendment to IEEE Std 802.11™-2020). “Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications. Amendment 1: Enhancements for High Efficiency WLAN.” IEEE Standard for Information technology — Telecommunications and information exchange between systems. Local and metropolitan area networks — Specific requirements.