wlanLLTFNoiseEstimate
Description
Examples
Estimate Noise Power Using L-LTF
Create a configuration object for a high-throughput packet. Set an initial signal-to-noise ratio of 10 dB.
cfg = wlanHTConfig; snr = 10;
Extract the OFDM information of the L-LTF in the configuration. Change the signal-to-noise ratio to remove the noise contribution from the null subcarriers.
ofdmInfo = wlanHTOFDMInfo("L-LTF",cfg);
snrValue = snr-10*log10(ofdmInfo.FFTLength/ofdmInfo.NumTones);
Extract the field indices that correspond to the L-LTF.
indLLTF = wlanFieldIndices(cfg,"L-LTF");
Generate a time-domain waveform for the configuration.
tx = wlanWaveformGenerator([1;0;0;1],cfg);
Perform the noise estimate for 100 separate noise realizations.
noiseEst = zeros(1,100); for i = 1:100 rx = awgn(tx,snrValue); rxLLTF = rx(indLLTF(1):indLLTF(2)); rxSym = wlanLLTFDemodulate(rxLLTF,cfg); noiseEst(i) = wlanLLTFNoiseEstimate(rxSym); end
Display the average value of the noise estimate, in dB.
disp(10*log10(mean(noiseEst)))
-10.0690
Input Arguments
rxSym
— Demodulated L-LTF or S1G-LTF1 OFDM symbols
3-D array
Demodulated L-LTF or S1G-LTF1 OFDM symbols, specified as an NST-by-2-by-NR array. NST is the number of occupied subcarriers. NR is the number of receive antennas. The two columns of the array correspond to demodulated L-LTF or S1G-LTF1 OFDM symbols.
Note
The function does not support noise estimation using the S1G-LTF1 field for the S1G 1 MHz mode.
Data Types: single
| double
Complex Number Support: Yes
Output Arguments
noiseEst
— Mean noise power estimate
positive real scalar
Mean noise power estimate in watts, returned as a positive real scalar.
Data Types: single
| double
More About
L-LTF
The L-LTF is the second field in the 802.11™ OFDM PLCP legacy preamble. The L-LTF is a component of EHT, HE, VHT, HT, and non-HT PPDUs.
Channel estimation, fine frequency offset estimation, and fine symbol timing offset estimation rely on the L-LTF.
The L-LTF is composed of a cyclic prefix (CP) followed by two identical long training symbols (C1 and C2). The CP consists of the second half of the long training symbol.
The L-LTF duration varies with channel bandwidth.
Channel Bandwidth (MHz) | Subcarrier Frequency Spacing ΔF (kHz) | Fast Fourier Transform (FFT) Period (TFFT = 1 / ΔF) | Cyclic Prefix or Training Symbol Guard Interval (GI2) Duration (TGI2 = TFFT / 2) | L-LTF Duration (TLONG = TGI2 + 2 × TFFT) |
---|---|---|---|---|
20, 40, 80, 160, and 320 | 312.5 | 3.2 μs | 1.6 μs | 8 μs |
10 | 156.25 | 6.4 μs | 3.2 μs | 16 μs |
5 | 78.125 | 12.8 μs | 6.4 μs | 32 μs |
Extended Capabilities
C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.
Version History
Introduced in R2023a
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