HE MU Transmission

Transmission Mode Options

The options for high-efficiency multiuser (HE MU) transmissions are:

• Orthogonal frequency-division multiple access (OFDMA)

• Full-band multiuser 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 SIGBCompression property of the wlanHEMUConfig object.

  • To enable SIGB compression, set the SIGBCompression property to 1 (true).

  • To disable SIGB compression, set the SIGBCompression property to 0 (false).

• For a 40, 80, or 160 MHz transmission, enable or disable SIGB compression by setting the AllocationIndex property of the wlanHEMUConfig object.

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 AllocationIndex property 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 Parameterization for Waveform Generation and Simulation 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.

Allocation Index

When creating a wlanHEMUConfig object, you must specify the value of the AllocationIndex property. Once the object is created, the AllocationIndex property is read-only.

The 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 scalar

  • 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

  • An 8-bit binary sequences specified as a string array

  • An 8-bit binary sequences specified as a cell array of character vectors

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 27-24 in [1]. 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 27.3.10.8.3 of [1].

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 27-23 of [1]. The RU Allocation subfield in the common field of HE-SIG-B consists of 8 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 27-26 and 27-27, of [1], 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	wlanHEMUConfig(a,'SIGBCompression', 1) Specify a as an integer in the interval [192, 199].	wlanHEMUConfig(a) Specify a as an integer in the interval [200, 207].	wlanHEMUConfig(a) Specify a as an integer in the interval [208, 215].	wlanHEMUConfig(a) Specify a as an integer in the interval [216, 223].
		The wlanHEMUConfig object sets the SIGBCompression property to 1 (true), and splits users between the two content channels.
Full-bandwidth MU-MIMO	wlanHEMUConfig(a,'SIGBCompression',0) Specify a as an integer in the interval [192, 199].	wlanHEMUConfig([x 114]) Specify a as an integer in the interval [200, 207].	wlanHEMUConfig([a 115 115 115]) wlanHEMUConfig([115 115 a 115]) wlanHEMUConfig([a 115 b 115]) Specify a and b as integers in the interval [208, 215].	wlanHEMUConfig([a 115 115 115 115 115 115 115]) wlanHEMUConfig([a 115 b 115 c 115 d 115]) wlanHEMUConfig([115 115 115 115 a 115 b 115]) wlanHEMUConfig([115 115 115 115 115 115 a 115]) wlanHEMUConfig([115 115 a 115 115 115 b 115]) Specify a, b, c, and d as integers in the interval [216, 223].
		The wlanHEMUConfig object sets the SIGBCompression property to 0 (false). All users are in content channel 1.
Full-bandwidth MU-MIMO	wlanHEMUConfig(a,'SIGBCompression',0) Specify a as an integer in the interval [192, 199].	wlanHEMUConfig([114 a]) Specify a as an integer in the interval [200, 207].	wlanHEMUConfig([115 a 115 115]) wlanHEMUConfig([115 115 115 a]) wlanHEMUConfig([115 a 115 b]) Specify a and b as integers in the interval [208, 215].	wlanHEMUConfig([115 a 115 115 115 115 115 115]) wlanHEMUConfig([115 a 115 b 115 c 115 d]) wlanHEMUConfig([115 115 115 115 115 a 115 b]) wlanHEMUConfig([115 115 115 115 115 115 115 a]) wlanHEMUConfig([115 115 115 a 115 115 115 b]) Specify a, b, c, and d as integers in the interval [216, 223].
		The wlanHEMUConfig object sets the SIGBCompression property to 0 (false). All users are in content channel 2.
Full bandwidth MU-MIMO	wlanHEMUConfig(a,'SIGBCompression',0) Specify a as an integer in the interval [192, 199].	wlanHEMUConfig([a b]) Specify a and b as integers in the interval [200, 207].	wlanHEMUConfig([a b c d]) Specify a, b, c, and d as integers in the interval [208, 215].	wlanHEMUConfig([a b c d e f g h]) Specify a, b, c, d, e, f, g, and h as integers in the interval [216, 223].
		The wlanHEMUConfig object sets the SIGBCompression property to 0 (false). Users are in their respective content channels. For example, in the 80 MHz transmission case, the users represented by allocation indices a and c are in content channel 1, and the users represented by allocation indices b and d are in content channel 2.
Mixed OFDMA and MU-MIMO	wlanHEMUConfig(a,'SIGBCompression',0) Specify a as an integer in the interval [0, 192].	wlanHEMUConfig([a b]) Specify a and b as integers in the interval [0, 199].	wlanHEMUConfig([a b c d]) Specify a, b, c, and d as integers in the interval [0, 207].	wlanHEMUConfig([a b c d e f g h]) Specify a, b, c, d, e, f, g, and h as integers in the interval [0, 215].
	20 MHz transmissions have only one content channel.	The wlanHEMUConfig object sets the SIGBCompression property to 0 (false). Users are in their respective content channels. For example, in the 80 MHz transmission case, the users represented by allocation indices a and c are in content channel 1, and the users represented by allocation indices b and d are in content channel 2.

References

[1] IEEE P802.11ax™/D4.1. “Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications. Amendment 1: Enhancements for High Efficiency WLAN.” Draft Standard for Information technology — Telecommunications and information exchange between systems. Local and metropolitan area networks — Specific requirements.

Related Topics

• WLAN PPDU Structure