Generate HTLTF waveform
Create a wlanHTConfig
object having a channel bandwidth of 40 MHz.
cfg = wlanHTConfig('ChannelBandwidth','CBW40');
Generate the corresponding HTLTF.
hltfOut = wlanHTLTF(cfg); size(hltfOut)
ans = 1×2
160 1
The cfg
parameters result in a 160sample waveform having only one column corresponding to a single stream transmission.
Generate an HTLTF having four transmit antennas and four spacetime streams.
Create a wlanHTConfig
object having an MCS of 31, four transmit antennas, and four spacetime 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
Generate the corresponding HTLTF.
hltfOut = wlanHTLTF(cfg);
Verify that the HTLTF output consists of four streams (one for each antenna).
size(hltfOut)
ans = 1×2
320 4
Because the channel bandwidth is 20 MHz and has four spacetime streams, the output waveform has four HTLTF and 320 timedomain samples.
cfg
— Format configurationwlanHTConfig
objectFormat configuration, specified as a wlanHTConfig
object.
The wlanHTLTF
function uses these properties:
ChannelBandwidth
— Channel bandwidth'CBW20'
(default)  'CBW40'
Channel bandwidth in MHz, specified as 'CBW20'
or 'CBW40'
.
Data Types: char
 string
NumTransmitAntennas
— Number of transmit antennasNumber of transmit antennas, specified as 1, 2, 3, or 4.
Data Types: double
NumSpaceTimeStreams
— Number of spacetime streamsNumber of spacetime streams in the transmission, specified as 1, 2, 3, or 4.
Data Types: double
NumExtensionStreams
— Number of extension spatial streamsNumber of extension spatial streams in the transmission, specified
as 0, 1, 2, or 3. When NumExtensionStreams
is
greater than 0, SpatialMapping
must be 'Custom'
.
Data Types: double
SpatialMapping
— Spatial mapping scheme'Direct'
(default)  'Hadamard'
 'Fourier'
 'Custom'
Spatial mapping scheme, specified as 'Direct'
,
'Hadamard'
, 'Fourier'
, or
'Custom'
. The default value
'Direct'
applies when
NumTransmitAntennas
and
NumSpaceTimeStreams
are equal.
Data Types: char
 string
SpatialMappingMatrix
— Spatial mapping matrixSpatial mapping matrix, specified as a scalar, matrix, or 3D
array. Use this property to rotate and scale the constellation mapper
output vector. This property applies when the SpatialMapping
property
is set to 'Custom'
. The spatial mapping matrix
is used for beamforming and mixing spacetime streams over the transmit
antennas.
When specified as a scalar, NumTransmitAntennas
= NumSpaceTimeStreams
=
1 and a constant value applies to all the subcarriers.
When specified as a matrix, the size must be (N_{STS} + N_{ESS})byN_{T}. N_{STS} is the number of spacetime streams. N_{ESS} is the number of extension spatial streams. N_{T} is the number of transmit antennas. The spatial mapping matrix applies to all the subcarriers. The first N_{STS} and last N_{ESS} rows apply to the spacetime streams and extension spatial streams respectively.
When specified as a 3D array, the size must be N_{ST}by(N_{STS} + N_{ESS})byN_{T}. N_{ST} is
the sum of the data and pilot subcarriers, as determined by ChannelBandwidth
. N_{STS} is
the number of spacetime streams. N_{ESS} is
the number of extension spatial streams. N_{T} is
the number of transmit antennas. In this case, each data and pilot
subcarrier can have its own spatial mapping matrix.
The table shows the ChannelBandwidth
setting
and the corresponding N_{ST}.
ChannelBandwidth  N_{ST} 

'CBW20'  56 
'CBW40'  114 
The calling function normalizes the spatial mapping matrix for each subcarrier.
Example: [0.5 0.3; 0.4 0.4; 0.5 0.8]
represents
a spatial mapping matrix having three spacetime streams and two transmit
antennas.
Data Types: double
Complex Number Support: Yes
y
— HTLTF waveformHTLTF waveform, returned as an (N_{S} × N_{HTLTF})byN_{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 HTLTF. 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  N_{S} 

'CBW20'  80 
'CBW40'  160 
Determination of the number of N_{HTLTF} is described in HTLTF.
Data Types: double
Complex Number Support: Yes
The high throughput long training field (HTLTF) is located between the HTSTF and data field of an HTmixed packet.
As described in IEEE^{®} Std 802.11™2012, Section 20.3.9.4.6, the receiver can use the HTLTF 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 HTLTF portion has one or two parts. The first part consists of one, two, or four HTLTFs that are necessary for demodulation of the HTData portion of the PPDU. These HTLTFs are referred to as HTDLTFs. The optional second part consists of zero, one, two, or four HTLTFs that can be used to sound extra spatial dimensions of the MIMO channel not utilized by the HTData portion of the PPDU. These HTLTFs are referred to as HTELTFs. Each HT long training symbol is 4 μs. The number of spacetime streams and the number of extension streams determines the number of HTLTF symbols transmitted.
Tables 2012, 2013 and 2014 from IEEE Std 802.112012 are reproduced here.
N_{STS} Determination  N_{HTDLTF} Determination  N_{HTELTF} Determination  

Table 2012 defines the number of spacetime streams (N_{STS}) based on the number of spatial streams (N_{SS}) from the MCS and the STBC field.  Table 2013 defines the number of HTDLTFs required for the N_{STS}.  Table 2014 defines the number of HTELTFs required for the number of extension spatial streams (N_{ESS}). N_{ESS} is defined in HTSIG_{2}.  



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.
As described in IEEE Std 802.112012, Section 20.1.4, high throughput mixed (HTmixed) format packets contain a preamble compatible with IEEE Std 802.112012, Section 18 and Section 19 receivers. NonHT (Section 18 and Section19) STAs can decode the nonHT fields (LSTF, LLTF, and LSIG). The remaining preamble fields (HTSIG, HTSTF, and HTLTF) 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 802.112012, Section 20.3.9.4. Support for the HTmixed format is mandatory.
The physical layer convergence procedure (PLCP) protocol data unit (PPDU) is the complete PLCP frame, including PLCP headers, MAC headers, the MAC data field, and the MAC and PLCP trailers.
[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.
wlanHTConfig
 wlanHTData
 wlanHTLTFChannelEstimate
 wlanHTLTFDemodulate
 wlanLLTF
^{[1]} IEEE Std 802.112012 Adapted and reprinted with permission from IEEE. Copyright IEEE 2012. All rights reserved.
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