wlanInterpretScramblerState

Recover bandwidth signaling from initial scrambler state

Since R2020b

Syntax

[bandwidth,dyn] = wlanInterpretScramblerState(scramInit)

[bandwidth,dyn] = wlanInterpretScramblerState(scramInit,idx1)

[___] = wlanInterpretScramblerState(___,serviceBits)

Description

[bandwidth,dyn] = wlanInterpretScramblerState(scramInit) recovers bandwidth signaling from initial scrambler state scramInit. The function returns bandwidth, the channel bandwidth, and dyn, an indication of whether bandwidth operation is dynamic or static.

[bandwidth,dyn] = wlanInterpretScramblerState(scramInit,idx1) specifies idx1, the dot11CurrentChannelCenterFrequencyIndex1 parameter, as defined in Table 17-9 of [1].

[___] = wlanInterpretScramblerState(___,serviceBits) additionally specifies the service field bits, serviceBits.

Examples

Recover Bandwidth Signaling from Initial Scrambler State

Configure and generate a non-HT Data signal with a channel bandwidth of 160 MHz and dynamic bandwidth operation.

bandwidth = 'CBW160';
cfg = wlanNonHTConfig(ChannelBandwidth=bandwidth,PSDULength=1, ...
    SignalChannelBandwidth=true,BandwidthOperation='Dynamic');
bits = randi([0 1],8*cfg.PSDULength,1,'int8');
[range,~] = scramblerRange(cfg);
scramInit = randi(range);
y = wlanNonHTData(bits,cfg,scramInit);

Transmit the waveform through an AWGN channel with an SNR of 50.

snr = 50;
noiseVarEst = 10^(-snr/10);
rx = awgn(y,snr);

Recover the frequency-domain signal by OFDM-demodulating the non-HT Data signal, specifying an OFDM symbol sampling offset.

field = 'NonHT-Data';
symOffset = 0.5;
sym = wlanNonHTOFDMDemodulate(rx,field,bandwidth,OFDMSymbolOffset=symOffset);

Extract the data subcarriers.

info = wlanNonHTOFDMInfo(field,bandwidth);
sym = sym(info.DataIndices,:);

Recover the first 20 MHz subchannel of the PSDU, enhancing the demapping of the OFDM subcarriers by specifying channel state information. Confirm that the received and transmitted PSDUs match.

csi = ones(48,1);
[psdu,scramInit] = wlanNonHTDataBitRecover(sym(1:48,:),noiseVarEst,csi,cfg);
isequal(bits,psdu)

ans = logical
   1

Recover and display bandwidth signaling by interpreting the scrambler state.

[bandwidth,dyn] = wlanInterpretScramblerState(scramInit)

bandwidth = 
'CBW160'

dyn = logical
   1

Recover Service Bits from 320 MHz Non-HT Duplicate Transmission

Create a non-HT configuration object with a channel bandwidth of 320 MHz. Signal the channel bandwidth and the bandwidth operation in the scrambler sequence.

cfg = wlanNonHTConfig(ChannelBandwidth="CBW320",SignalChannelBandwidth=true, ...
    BandwidthOperation="Dynamic");

Generate a time-domain waveform for the configuration. To simulate a noiseless channel, set the received waveform equal to the transmitted waveform.

tx = wlanWaveformGenerator([1;0;0;1],cfg);
rx = tx;
noiseVarEst = 0;

Get field indices for the non-HT data field. Extract the part of the received waveform that corresponds to the data field.

dataInd = wlanFieldIndices(cfg,"NonHT-Data");
rxData = rx(dataInd(1):dataInd(2),:);

Demodulate the data field. Extract the data symbols.

rxSym = wlanNonHTOFDMDemodulate(rxData,"NonHT-Data",cfg);
info = wlanNonHTOFDMInfo("NonHT-Data",cfg);
dataSym = rxSym(info.DataIndices,:,:);

Recover the PSDU bits, initial scrambler state, and service bits from the first 20 MHz subchannel.

[psdu,scramInit,serviceBits] = wlanNonHTDataBitRecover(dataSym(1:48,:),noiseVarEst,cfg);

Interpret the scrambler state, using the default $$dot11CurrentChannelCenterFrequencyIndex1$$value of 0.

idx1 = 0;
[bandwidth,dyn] = wlanInterpretScramblerState(scramInit,idx1,serviceBits);

Display the recovered channel bandwidth and bandwidth operation indicator. They match the values you specified when you created the wlanNonHTConfig object.

disp(bandwidth)

CBW320

disp(dyn)

   1

Input Arguments

scramInit — Initial scrambler state

integer in the interval [1, 127] | binary-valued column vector

Initial scrambler state, specified as an integer in the interval [1, 127], or the corresponding binary-valued column vector of length 7.

Section 17.3.5.5 of [1] specifies the scrambling and descrambling process applied to the transmitted data. The header and data fields that follow the scrambler initialization field (including data padding bits) are scrambled by XORing each bit with a length-127 periodic sequence generated by the polynomial S(x) = x⁷ + x⁴ + 1. The octets of the PSDU are placed into a bit stream, and, within each octet, bit 0 (LSB) is first and bit 7 (MSB) is last. This figure demonstrates the sequence generation and XOR operation.

Conversion from integer to bits uses left-MSB orientation. For example, initializing the scrambler with decimal 1, the bits map to these elements.

Element	X7	X6	X5	X4	X3	X2	X1
Bit Value	0	0	0	0	0	0	1

To generate the bit stream equivalent to a decimal, use the int2bit function. For example, for decimal 1:

int2bit(1,7)'
ans =

     0     0     0     0     0     0     1

Example: [1; 0; 1; 1; 1; 0; 1] conveys the scrambler initialization state of 93 as a binary-valued column vector.

Data Types: double

idx1 — dot11CurrentChannelCenterFrequencyIndex1 parameter

0 (default) | scalar in the interval [0, 200]

dot11CurrentChannelCenterFrequencyIndex1 parameter, as defined in Table 17-9 of [1], specified as a scalar in the interval [0, 200].

Data Types: double

serviceBits — Service field bits

binary column vector of length 16

Since R2025a

Service field bits, specified as a binary column vector of length 16.

Output Arguments

bandwidth — Recovered channel bandwidth

'CBW20' | 'CBW40' | 'CBW80' | 'CBW160' | 'CBW320' | 'CBW80+80' | 'Unknown'

Recovered channel bandwidth, returned as one of these values.

• 'CBW20' — Channel bandwidth of 20 MHz

• 'CBW40' — Channel bandwidth of 40 MHz

• 'CBW80' — Channel bandwidth of 80 MHz

• 'CBW160' — Channel bandwidth of 160 MHz

• 'CBW320' — Channel bandwidth of 320 MHz

• 'CBW80+80' — Channel bandwidth of 160 MHz comprising two non-adjacent 80 MHz channels

• 'Unknown' — Invalid combination of input values

Data Types: char

dyn — Indication of whether bandwidth operation is dynamic or static

0 | 1

Indication of whether bandwidth operation is dynamic or static, returned as a logical 1 or 0. A value of 0 indicates static bandwidth operation. A value of 1 indicates dynamic bandwidth operation.

Data Types: logical

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.

Extended Capabilities

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

Version History

Introduced in R2020b

R2025a: Service field bits input

The wlanInterpretScramblerState function now accepts decoded service field bits. To supply these bits, specify the serviceBits input. This input enables you to interpret the scrambler state of 320 MHz non-HT duplicate packets.