wlanHTLTFDemodulate

Demodulate HT-LTF waveform

Syntax

sym = wlanHTLTFDemodulate(rx,cfg)

sym = wlanHTLTFDemodulate(rx,cfg,symOffset)

Description

sym = wlanHTLTFDemodulate(rx,cfg) returns the demodulated HT-LTF¹ by demodulating received time-domain HT-LTF signal rx by using transmission parameters cfg. The input signal is a component of the HT-mixed format PPDU.

sym = wlanHTLTFDemodulate(rx,cfg,symOffset) specifies the OFDM symbol sampling offset as a fraction of the cyclic prefix length.

Examples

Demodulate HT-LTF in AWGN

Create an HT configuration object.

cfg = wlanHTConfig;

Generate an HT-LTF signal based on the object.

x = wlanHTLTF(cfg);

Pass the HT-LTF signal through an AWGN channel.

y = awgn(x,20);

Demodulate the received signal.

z = wlanHTLTFDemodulate(y,cfg);

Display the scatter plot of the demodulated signal.

scatterplot(z)

Demodulate 2x2 HT-LTF with OFDM Symbol Offset

Create an HT configuration object having two transmit antennas and two space-time streams.

cfg = wlanHTConfig('NumTransmitAntennas',2,'NumSpaceTimeStreams',2, ...
    'MCS',8);

Generate the HT-LTF based on the configuration object.

x = wlanHTLTF(cfg);

Pass the HT-LTF signal through an AWGN channel.

y = awgn(x,10);

Demodulate the received signal. Set the OFDM symbol offset to 0.5, which corresponds to 1/2 of the cyclic prefix length.

z = wlanHTLTFDemodulate(y,cfg,0.5);

Input Arguments

rx — Received time-domain signal

complex-valued matrix

Received time-domain signal, specified as a complex-valued matrix of size N_s-by-N_r.

• N_s is the number of time-domain samples. If N_s is not an integer multiple of the OFDM symbol length, L_s, for the specified field,then the function ignores the remaining mod(Ns,Ls) symbols.

• N_r is the number of receive antennas.

Data Types: single | double
Complex Number Support: Yes

cfg — HT format configuration

wlanHTConfig object

HT format configuration, specified as a wlanHTConfig object.

symOffset — OFDM symbol sampling offset

0.75 (default) | scalar in the interval [0, 1]

OFDM symbol sampling offset, as a fraction of the cyclic prefix length, specified as a scalar in the interval [0, 1].

The value that you specify indicates the start location for OFDM demodulation relative to the beginning of the cyclic prefix.

Example: 0.45

Data Types: single | double

Output Arguments

sym — Demodulated frequency-domain signal

complex-valued array

Demodulated frequency-domain signal, returned as a complex-valued array of size N_sc-by-N_sym-by-N_r.

• N_sc is the number of active occupied subcarriers in the demodulated field.

• N_sym is the number of OFDM symbols.

• N_r is the number of receive antennas.

Data Types: single | 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

High throughput mixed (HT-mixed) format devices support a mixed mode in which the PLCP header is compatible with HT and non-HT modes.

PPDU

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.

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

R2023b: Single precision support

This function supports single-precision values for its numeric input arguments.