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Packet Size and Duration Dependencies

WLAN standards specify a maximum packet duration (TXTIME) for the various formats. The EHT, WUR, HE, and S1G formats additionally specify the maximum PSDU length (PSDU_LENGTH) and number of symbols (NSYM). These variables are functions of transmission properties that you set using WLAN Toolbox™ configuration objects. The software validates the settings of a WLAN format-specific configuration object when you use the object. Command-line feedback tells you when the configuration violates the packet size or duration limits.

This table lists relevant properties that determine the packet duration and PSDU length for the various WLAN formats. It also provides references to the IEEE® standards for further details.

WLAN FormatLength-Related ValidationRelevant and Dependent Properties
EHT

TXTIME and PSDU_LENGTH require validation.

TXTIME and PSDU_LENGTH are defined by the equations in Section 36.4.3 of [4].

As specified by aPPDUMaxTime and aPSDUMaxLength in Table 36-70, the maximum TXTIME is 5.484 ms and the maximum PSDU_LENGTH is 15,523,198 octets.

EHT multi-user

For a non-OFDMA packet, TXTIME and PSDU_LENGTH depend on ChannelBandwidth and NumUsers. For OFDMA, the relevant property is AllocationIndex. Beyond this, the properties are the same in the non-OFDMA and OFDMA cases.

PSDU_LENGTH is different for each user in the configuration, but TXTIME is the same. For PSDU_LENGTH:

  • Can vary per user:

    1. NumSpaceTimeStreams

    2. MCS

    3. ChannelCoding

    4. APEPLength

  • Same for all users:

    1. NumExtraEHTLTFSymbols

    2. EHTSIGMCS

For TXTIME:

  1. All the above PSDU_LENGTH properties

  2. GuardInterval

  3. EHTLTFType

EHT trigger-based

PSDU_LENGTH:

  1. ChannelBandwidth

  2. RUSize

  3. NumSpaceTimeStreams

  4. MCS

  5. ChannelCoding

  6. PreFECPaddingFactor

  7. LDPCExtraSymbol

  8. PEDisambiguity

  9. NumEHTLTFSymbols

TXTIME:

  1. All the above PSDU_LENGTH properties

  2. GuardInterval

  3. EHTLTFType

WUR

TXTIME requires validation.

TXTIME is defined by the equations in Section 30.4.1 of [3].

As specified by aPPDUMaxTime in Table 30-3, the maximum TXTIME is 2.972 ms.

  1. DataRate

  2. PSDULength

These are properties of a wlanWURSubchannel object.

HE

TXTIME and PSDU_LENGTH require validation.

TXTIME and PSDU_LENGTH are defined by the equations in Section 27.4.3 of [2].

As specified by aPPDUMaxTime and aPSDUMaxLength in Table 27-53, the maximum TXTIME is 5.484 ms and the maximum PSDU_LENGTH is 6,500,631 octets.

HE single user and single user extended range

PSDU_LENGTH

  1. ChannelBandwidth

  2. NumSpaceTimeStreams

  3. STBC

  4. MCS

  5. DCM

  6. ChannelCoding

  7. APEPLength

TXTIME

  1. All the above PSDU_LENGTH properties

  2. ExtendedRange

  3. GuardInterval

  4. HELTFType

  5. HighDoppler

  6. MidamblePeriodictiy(he_1)

HE multi-user

PSDU_LENGTH is different for each user in the configuration, but the transmit time is the same. For PSDU_LENGTH:

  • Can vary per user:

    1. User RU size, which is based on:

      1. AllocationIndex

      2. ChannelBandwidth, which depends on AllocationIndex

      3. Lower26ToneRU(he_2)

      4. Upper26ToneRU(he_2)

    2. NumSpaceTimeStreams

    3. MCS

    4. DCM

    5. ChannelCoding

    6. APEPLength

  • Same for all users:

    • STBC

For TXTIME:

  1. The above PSDU_LENGTH properties that can vary per user

  2. GuardInterval

  3. HELTFType

  4. SIGBCompression(he_3)(he_4)

  5. SIGBMCS

  6. SIGBDCM

  7. HighDoppler

  8. MidamblePeriodictiy(he_1)

HE trigger-based

PSDU_LENGTH

  1. FeedbackNDPhe_5

  2. TriggerMethod

  3. RUSize

  4. ChannelBandwidth

  5. NumSpaceTimeStreams

  6. STBC

  7. MCS

  8. DCM

  9. ChannelCoding

  10. LDPCExtraSymbol

  11. PreFECPaddingFactor

  12. NumDataSymbols

  13. NumHELTFSymbols

  14. PEDisambiguity

TXTIME:

  1. All the above PSDU_LENGTH properties

  2. GuardInterval

  3. HELTFType

  4. DefaultPEDuration

  5. HighDoppler

  6. MidamblePeriodicity

Notes:

(he_1) MidamblePeriodictiy is only relevant when HighDoppler is true.

(he_2) Lower26ToneRU and Upper26ToneRU are only relevant if the user for which the PSDU_LENGTH is derived is allocated on either of these RUs.

(he_3) If SIG-B compression is used, there is a common field in the HE-SIG-B field that affects the TXTIME computation.

(he_4) The SIGBCompression property is only relevant when a full-band 20 MHz allocation is specified.

(he_5)PSDU_LENGTH is always 0 when FeedbackNDP is true because there is no data field in this case.

DMG

TXTIME requires validation.

TXTIME is defined by the equations in Section 20.12.3 of [1].

As specified by aPPDUMaxTime in Table 20-32, the maximum TXTIME is 2 ms.

  1. MCS (dmg_1)

  2. PSDULength

  3. TrainingLength (dmg_1)

  4. PacketType (dmg_1)

  5. BeamTrackingRequest (dmg_1)

Notes:

(dmg_1) The property helps determine whether the packet is a beam refinement protocol (BRP) packet containing training fields or if it is a general packet signaling the number of fields to append. For more information, see [1]

S1G

TXTIME, PSDU_LENGTH, and NSYM require validation.

The equations for all three of these characteristics are in Section 23.4.3 of [1], and the maximum TXTIME and PSDU_LENGTH are defined in Table 23-40.

  • As specified by aPPDUMaxTime, the maximum TXTIME is 27.92 ms. This TXTIME is the maximum PPDU duration for an S1G_1M PPDU with:

    • A bandwidth of 1 MHz

    • S1G MCS set to 10

    • One spatial stream, limited by a PSDU length of 511 octets.

  • As specified by aPPDUMaxLength, the maximum PSDU_LENGTH is 797,159 octets. This PSDU length is the maximum length in octets for an S1G SU PPDU with:

    • A bandwidth of 16 MHz

    • S1G-MCS set to 9

    • Four spatial streams, limited by 511 data symbols supported by the Length field in the S1G SIG field, excluding the SERVICE field and tail bits.

  • The maximum NSYM is 511.

For TXTIME, the relevant properties are:

  1. ChannelBandwidth

  2. STBC (s1g_1)

  3. GuardInterval

  4. ChannelCoding (MU)

  5. APEPLength (MU)

  6. PSDULength – This property is read-only. When undefined, PSDULength is returned as empty of size 1×0. An empty return can happen when the set of property values for the object define an invalid state. (MU)

  7. MCS (MU)

  8. NumSpaceTimeStreams (MU)

  9. NumUsers

For PSDU_LENGTH and NSYM, the relevant properties are:

  1. ChannelBandwidth

  2. STBC (s1g_1)

  3. ChannelCoding (MU)

  4. APEPLength (MU)

  5. PSDULength – This property is read-only. When undefined, PSDULength is returned as empty, []. An empty return can happen when the set of property values for the object define an invalid state. (MU)

  6. MCS (MU)

  7. NumSpaceTimeStreams (MU)

  8. NumUsers

Notes:

(s1g_1) The property is relevant only when NumUsers = 1.

(MU) The property has multiple values for multi-user operation.

VHT

TXTIME requires validation.

TXTIME is defined by the equations in Section 21.4.3 in [1].

As specified by aPPDUMaxTime in Table 21-29, the maximum TXTIME is 5.484 ms.

  1. ChannelBandwidth

  2. STBC (vht_1)

  3. GuardInterval

  4. ChannelCoding (MU)

  5. APEPLength (MU)

  6. PSDULength – This property is read only. When undefined, it is returned as an empty of size 1×0.(MU)

  7. MCS (MU)

  8. NumSpaceTimeStreams (MU)

  9. NumUsers

Notes:

(vht_1) The property is relevant only when NumUsers = 1.

(MU) The property has multiple values for multi-user operation.

HT

TXTIME requires validation.

TXTIME is defined by the equations in Section 19.4.3 of [1].

As specified in Table 9-19, the maximum TXTIME for HT mixed PPDUs is 5.484 ms.

  1. ChannelBandwidth

  2. GuardInterval

  3. ChannelCoding

  4. PSDULength

  5. MCS

  6. NumSpaceTimeStreams

  7. NumExtensionStreams

non-HT

TXTIME requires validation.

TXTIME for OFDM modulation is defined by the equations in Section 17.4.3 of [1].

Based on equation 17–29 and a valid combination of property settings, the maximum TXTIME is 21.936 ms. This is the maximum transmit time of a non-HT packet with a bandwidth of 5 MHz. It is equal to 5.484 ms, the corresponding time for a 20 MHz packet, multiplied by four. This is because 5 MHz waveforms are generated by underclocking 20 MHz waveforms by a factor of four.

  1. Modulation (non-ht_1)

  2. PSDULength

  3. MCS (non-ht_1)

  4. DateRate (non-ht_1)

Notes:

(non-ht_1) DataRate or MCS might be relevant depending on the Modulation setting.

You can use the wlanAPEPLength and wlanPSDULength functions to calculate APEP and PSDU lengths for a PHY format configuration given the packet transmission time or the number of symbols in the data field.

References

[1] IEEE Std 802.11™-2020 (Revision of IEEE Std 802.11-2016). “Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications.” IEEE Standard for Information Technology — Telecommunications and Information Exchange between Systems — Local and Metropolitan Area Networks — Specific Requirements.

[2] 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.

[3] IEEE Std 802.11ba™-2021. “Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications. Amendment 3: Wake-Up Radio Operation.” IEEE Standard for Information Technology — Telecommunications and Information Exchange between Systems. Local and Metropolitan Area Networks — Specific Requirements.

See Also

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