wlanHTLTF

Generate HT-LTF waveform

Syntax

y = wlanHTLTF(cfg)

y = wlanHTLTF(cfg,OversamplingFactor=osf)

Description

y = wlanHTLTF(cfg) generates an HT-LTF¹ time-domain waveform for HT-mixed transmissions with parameters specified in cfg.

y = wlanHTLTF(cfg,OversamplingFactor=osf) generates an oversampled HT-LTF waveform with the specified oversampling factor.

Examples

Generate Single-Stream HT-LTF Waveform

Create a wlanHTConfig object having a channel bandwidth of 40 MHz.

cfg = wlanHTConfig('ChannelBandwidth','CBW40');

Generate the corresponding HT-LTF.

hltfOut = wlanHTLTF(cfg);
size(hltfOut)

ans = 1×2

   160     1

The cfg parameters result in a 160-sample waveform having only one column corresponding to a single stream transmission.

Generate Oversampled HT-LTF with Four Space-Time Streams

Generate an oversampled HT-LTF waveform with four transmit antennas and four space-time streams.

Create a wlanHTConfig configuration with MCS index 31, four transmit antennas, and four space-time streams.

cfg = wlanHTConfig('MCS',31,'NumTransmitAntennas',4,'NumSpaceTimeStreams',4)

cfg = 
  wlanHTConfig with properties:

       ChannelBandwidth: 'CBW20'
    NumTransmitAntennas: 4
    NumSpaceTimeStreams: 4
         SpatialMapping: 'Direct'
                    MCS: 31
          GuardInterval: 'Long'
          ChannelCoding: 'BCC'
             PSDULength: 1024
         AggregatedMPDU: 0
     RecommendSmoothing: 1

Specify an oversampling factor and generate the corresponding HT-LTF waveform.

osf = 4;
y = wlanHTLTF(cfg,OversamplingFactor=osf);

Verify that the waveform output consists of four streams (one for each antenna). Because the channel bandwidth is 20 MHz and the waveform is oversampled and has four space-time streams, the waveform has four HT-LTF and 1280 time-domain samples.

size(y)

ans = 1×2

        1280           4

Input Arguments

cfg — Transmission parameters

wlanHTConfig object

Transmission parameters, specified as a wlanHTConfig object.

osf — Oversampling factor

1 (default) | scalar greater than or equal to 1

Oversampling factor, specified as a scalar greater than or equal to 1. The oversampled cyclic prefix length must be an integer number of samples.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

Output Arguments

y — HT-LTF waveform

matrix

HT-LTF waveform, returned as an (N_S × N_HTLTF)-by-N_T matrix. N_S is the number of time domain samples per N_HTLTF, where N_HTLTF is the number of OFDM symbols in the HT-LTF. N_T is the number of transmit antennas.

N_S is proportional to the channel bandwidth. Each symbol contains 80 time samples per 20 MHz channel.

ChannelBandwidth	NS
'CBW20'	80
'CBW40'	160

Determination of the number of N_HTLTF is described in HT-LTF.

Data Types: double
Complex Number Support: Yes

More About

HT-LTF

The high throughput long training field (HT-LTF) is located between the HT-STF and data field of an HT-mixed packet.

As described in Section 19.3.9.4.6 of IEEE^® Std 802.11™-2016, the receiver can use the HT-LTF to estimate the MIMO channel between the set of QAM mapper outputs (or, if STBC is applied, the STBC encoder outputs) and the receive chains. The HT-LTF portion has one or two parts. The first part consists of one, two, or four HT-LTFs that are necessary for demodulation of the HT-Data portion of the PPDU. These HT-LTFs are referred to as HT-DLTFs. The optional second part consists of zero, one, two, or four HT-LTFs that can be used to sound extra spatial dimensions of the MIMO channel not utilized by the HT-Data portion of the PPDU. These HT-LTFs are referred to as HT-ELTFs. Each HT long training symbol is 4 μs. The number of space-time streams and the number of extension streams determines the number of HT-LTF symbols transmitted.

Tables 19-12, 19-13 and 90-14 from IEEE Std 802.11-2012 are reproduced here.

NSTS Determination	NHTDLTF Determination	NHTELTF Determination
Table 19-12 defines the number of space-time streams (NSTS) based on the number of spatial streams (NSS) from the MCS and the STBC field.	Table 19-13 defines the number of HT-DLTFs required for the NSTS.	Table 19-14 defines the number of HT-ELTFs required for the number of extension spatial streams (NESS). NESS is defined in HT-SIG2.
NSS from MCS STBC field NSTS 1 0 1 1 1 2 2 0 2 2 1 3 2 2 4 3 0 3 3 1 4 4 0 4	NSTS NHTDLTF 1 1 2 2 3 4 4 4	NESS NHTELTF 0 0 1 1 2 2 3 4

Additional constraints include:

• N_HTLTF = N_HTDLTF + N_HTELTF ≤ 5.

• N_STS + N_ESS ≤ 4.

  • When N_STS = 3, N_ESS cannot exceed one.

  • If N_ESS = 1 when N_STS = 3 then N_HTLTF = 5.

HT-mixed

As described in IEEE Std 802.11-2012, Section 20.1.4, high throughput mixed (HT-mixed) format packets contain a preamble compatible with IEEE Std 802.11-2012, Section 18 and Section 19 receivers. Non-HT (Section 18 and Section19) STAs can decode the non-HT fields (L-STF, L-LTF, and L-SIG). The remaining preamble fields (HT-SIG, HT-STF, and HT-LTF) are for HT transmission, so the Section 18 and Section 19 STAs cannot decode them. The HT portion of the packet is described in IEEE Std 802.11-2012, Section 20.3.9.4. Support for the HT-mixed format is mandatory.

PPDU

The physical layer (PHY) protocol data unit (PPDU) is the complete physical layer convergence procedure (PLCP) frame, including PLCP headers, MAC headers, the MAC data field, and the MAC and PLCP trailers.

References

[1] IEEE Std 802.11™-2012 IEEE Standard for Information technology — Telecommunications and information exchange between systems — Local and metropolitan area networks — Specific requirements — Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Version History

Introduced in R2015b