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flushFilter

Flush transmit filter

Since R2021a

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    Syntax

    out = flushFilter(obj)

    Description

    out = flushFilter(obj) passes zeros through the transmit filter in the input waveform generator to flush the residual data samples that remain in the filter state. The function returns the residual data samples.

    You must call the input waveform generator System object (not only create the object) prior to using the flushFilter object function. The number of zeros passed through the transmit filter depends on the filter delay. This object function is required for the receiver simulations to recover all of the bits in the last physical layer frame.

    example

    Examples

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    Open Live Script

    Get information from a dvbs2WaveformGenerator System object by using the info function. Then retrieve the filter residual samples by using the flushFilter object function.

    This example uses MAT-files with LDPC parity matrices. If the MAT-files are not available on the path, download and unzip the MAT-files by entering this code at the MATLAB command prompt.

    if ~exist('dvbs2xLDPCParityMatrices.mat','file')
    if ~exist('s2xLDPCParityMatrices.zip', 'file')
        url = 'https://ssd.mathworks.com/supportfiles/spc/satcom/DVB/s2xLDPCParityMatrices.zip';
        websave('s2xLDPCParityMatrices.zip',url);
        unzip('s2xLDPCParityMatrices.zip');
    end
addpath('s2xLDPCParityMatrices');
end

    Specify the number of physical layer (PL) frames per stream.

    numFrames = 1;

    Create a Digital Video Broadcasting standard (DVB-S2) System object, and then specify its properties.

    s2WaveGen = dvbs2WaveformGenerator;
s2WaveGen.NumInputStreams = 2;
s2WaveGen.MODCOD = [21 16];
s2WaveGen.DFL   = 47008;
s2WaveGen.ISSYI = true;
s2WaveGen.SamplesPerSymbol = 2;
disp(s2WaveGen)
      dvbs2WaveformGenerator with properties:

           StreamFormat: "TS"
        NumInputStreams: 2
               FECFrame: "normal"
                 MODCOD: [21 16]
                    DFL: 47008
          ScalingMethod: "outer radius as 1"
              HasPilots: 0
          RolloffFactor: 0.3500
    FilterSpanInSymbols: 10
       SamplesPerSymbol: 2
                  ISSYI: true
             ISCRFormat: "short"

  Show all properties

    Get the characteristic information about the DVB-S2 waveform generator.

    info(s2WaveGen)
    ans = struct with fields:
      ModulationScheme: {'16APSK'  '8PSK'}
    LDPCCodeIdentifier: {'5/6'  '8/9'}

    Create the bit vector of input information bits, data, of concatenated TS user packets.

    syncBits = [0 1 0 0 0 1 1 1]';       % Sync byte for TS packet is 47 Hex
pktLen = 1496;                       % UP length without sync bits is 1496
data =  cell(1,s2WaveGen.NumInputStreams);
for i = 1:s2WaveGen.NumInputStreams
    numPkts = s2WaveGen.MinNumPackets(i)*numFrames;
    txRawPkts = randi([0 1],pktLen,numPkts);
    ISSY = randi([0 1],16,numPkts);   % ISCRFormat is 'short' by default
                                      % 'short' implies the default length of ISSY as 2 bytes
    txPkts = [repmat(syncBits,1,numPkts);txRawPkts;ISSY];    % ISSY is appended at the end of UP
    data{i} = txPkts(:);
end

    Generate a DVB-S2 time-domain waveform using the information bits.

    txWaveform = [s2WaveGen(data)];

    Check the filter residual data samples that remain in the filter delay.

    flushFilter(s2WaveGen)
    ans = 20×1 complex

   0.0153 + 0.4565i
   0.2483 + 0.5535i
   0.3527 + 0.3972i
   0.3541 - 0.0855i
   0.3505 - 0.4071i
   0.4182 - 0.1962i
   0.5068 + 0.0636i
   0.4856 - 0.1532i
   0.3523 - 0.4153i
   0.1597 - 0.2263i
      ⋮
    Open Live Script

    Recover user packets (UPs) for multiple physical layer (PL) frames in a single transport stream Digital Video Broadcasting Satellite Second Generation (DVB-S2) transmission.

    This example uses MAT-files with LDPC parity matrices. If the MAT-files are not available on the path, download and unzip the MAT-files by entering this code at the MATLAB command prompt.

    if ~exist('dvbs2xLDPCParityMatrices.mat','file')
    if ~exist('s2xLDPCParityMatrices.zip','file')
        url = 'https://ssd.mathworks.com/supportfiles/spc/satcom/DVB/s2xLDPCParityMatrices.zip';
        websave('s2xLDPCParityMatrices.zip',url);
        unzip('s2xLDPCParityMatrices.zip');
    end
addpath('s2xLDPCParityMatrices');
end

    Specify the number of PL frames per stream. Create a DVB-S2 System object.

    nFrames = 2;
s2WaveGen = dvbs2WaveformGenerator;

    Create the bit vector of information bits, data, of concatenated TS UPs.

    syncBits = [0 1 0 0 0 1 1 1]';    % Sync byte for TS packet is 47 Hex
pktLen = 1496;                    % UP length without sync bits is 1496
numPkts = s2WaveGen.MinNumPackets*nFrames;
txRawPkts = randi([0 1],pktLen,numPkts);
txPkts = [repmat(syncBits,1,numPkts); txRawPkts];
data = txPkts(:);

    Generate the DVB-S2 time-domain waveform using the input information bits. Flush the transmit filter to handle the filter delay and recover the complete last frame.

    txWaveform = [s2WaveGen(data); flushFilter(s2WaveGen)];

    Add additive white Gaussian noise (AWGN) to the generated waveform.

    sps = s2WaveGen.SamplesPerSymbol; 
EsNodB = 1;
snrdB = EsNodB - 10*log10(sps);
rxIn = awgn(txWaveform,snrdB,'measured');

    Create a raised cosine receiver filter.

    rxFilter = comm.RaisedCosineReceiveFilter( ...
      'RolloffFactor',s2WaveGen.RolloffFactor, ...
       'InputSamplesPerSymbol',sps,...
       'DecimationFactor',sps);
s = coeffs(rxFilter);
rxFilter.Gain = sum(s.Numerator);

    Apply matched filtering and remove the filter delay.

    filtOut = rxFilter(rxIn);
rxFrame = filtOut(rxFilter.FilterSpanInSymbols+1:end);

    Recover UPs. Display the number of frames lost and the UP cyclic redundancy check (CRC) status.

    [bits,FramesLost,pktCRCStat] = dvbs2BitRecover(rxFrame,10^(-EsNodB/10));
disp(FramesLost)
         0

    disp(pktCRCStat)
        {20×1 logical}
    Open Live Script

    Get information from a dvbs2xWaveformGenerator System object by using the info function. Then retrieve the filter residual samples by using the flushFilter object function.

    This example uses MAT-files with LDPC parity matrices. If the MAT-files are not available on the path, download and unzip the MAT-files by entering this code at the MATLAB command prompt.

    if ~exist('dvbs2xLDPCParityMatrices.mat','file')
    if ~exist('s2xLDPCParityMatrices.zip','file')
        url = 'https://ssd.mathworks.com/supportfiles/spc/satcom/DVB/s2xLDPCParityMatrices.zip';
        websave('s2xLDPCParityMatrices.zip',url);
        unzip('s2xLDPCParityMatrices.zip');
    end
addpath('s2xLDPCParityMatrices');
end

    Specify the number of physical layer (PL) frames per stream.

    numFrames = 2;

    Create a Digital Video Broadcasting Satellite Second Generation extended (DVB-S2X) System object and specify its properties. Use time slicing technique and variable coding and modulation configuration mode.

    s2xWaveGen = dvbs2xWaveformGenerator();
s2xWaveGen.HasTimeSlicing = true;
s2xWaveGen.NumInputStreams = 2;
s2xWaveGen.PLSDecimalCode = [135 145];   % QPSK 9/20 and 8PSK 25/36
s2xWaveGen.DFL = [18048 44656];
s2xWaveGen.PLScramblingIndex = [0 1];
disp(s2xWaveGen)
      dvbs2xWaveformGenerator with properties:

           StreamFormat: "TS"
         HasTimeSlicing: true
        NumInputStreams: 2
         PLSDecimalCode: [135 145]
                    DFL: [18048 44656]
      PLScramblingIndex: [0 1]
          RolloffFactor: 0.3500
    FilterSpanInSymbols: 10
       SamplesPerSymbol: 4
                  ISSYI: false

  Show all properties

    Get the characteristic information about the DVB-S2X waveform generator.

    info(s2xWaveGen)
    ans = struct with fields:
              FECFrame: {'normal'  'normal'}
      ModulationScheme: {'QPSK'  '8PSK'}
    LDPCCodeIdentifier: {'9/20'  '25/36'}

    Create the bit vector of input information bits, data, of concatenated TS user packets for each input stream.

    syncBits = [0 1 0 0 0 1 1 1]';       % Sync byte for TS packet is 47 Hex
pktLen = 1496;                       % UP length without sync bits is 1496
data =  cell(1, s2xWaveGen.NumInputStreams);
for i = 1:s2xWaveGen.NumInputStreams
    numPkts = s2xWaveGen.MinNumPackets(i)*numFrames;
    txRawPkts = randi([0 1], pktLen, numPkts);
    txPkts = [repmat(syncBits, 1, numPkts); txRawPkts];
    data{i} = txPkts(:);
end

    Generate a DVB-S2X time-domain waveform using the information bits.

    txWaveform = s2xWaveGen(data);

    Check the filter residual data samples that remain in the filter delay.

    flushFilter(s2xWaveGen)
    ans = 40×1 complex

  -0.2412 - 0.0143i
  -0.2619 - 0.0861i
  -0.2726 - 0.1337i
  -0.2511 - 0.1597i
  -0.1851 - 0.1680i
  -0.0780 - 0.1602i
   0.0448 - 0.1288i
   0.1598 - 0.0751i
   0.2482 - 0.0049i
   0.3026 + 0.0702i
      ⋮
    Open Live Script

    Get information from a ccsdsTMWaveformGenerator System object by using the info function. Then retrieve the filter residual samples by using the flushFilter object function.

    Create a Consultative Committee for Space Data Systems (CCSDS) Telemetry (TM) System object. Set the waveform type as synchronization and channel coding with low-density parity-check (LDPC) channel coding. Display the properties.

    tmWaveGen = ccsdsTMWaveformGenerator;
tmWaveGen.WaveformSource = "synchronization and channel coding";
tmWaveGen.ChannelCoding = "LDPC";
tmWaveGen.NumBitsInInformationBlock = 1024;
tmWaveGen.Modulation = "QPSK";
tmWaveGen.CodeRate = "1/2";
disp(tmWaveGen)
      ccsdsTMWaveformGenerator with properties:

               WaveformSource: "synchronization and channel coding"
                HasRandomizer: true
                       HasASM: true
                    PCMFormat: "NRZ-L"

   Channel coding
                ChannelCoding: "LDPC"
    NumBitsInInformationBlock: 1024
                     CodeRate: "1/2"
                 IsLDPCOnSMTF: false

   Digital modulation and filter
                   Modulation: "QPSK"
           PulseShapingFilter: "root raised cosine"
                RolloffFactor: 0.3500
          FilterSpanInSymbols: 10
             SamplesPerSymbol: 10

  Use get to show all properties

    Specify the number of transfer frames.

    numTF = 20;

    Get the characteristic information about the CCSDS TM waveform generator.

    info(tmWaveGen)
    ans = struct with fields:
         ActualCodeRate: 0.5000
       NumBitsPerSymbol: 2
    SubcarrierFrequency: []

    Generate the input bits for the CCSDS TM waveform generator, and then generate the waveform.

    bits = randi([0 1], tmWaveGen.NumInputBits*numTF,1);
waveform = tmWaveGen(bits);

    Check the filter residual data samples that remain in the filter delay.

    flushFilter(tmWaveGen)
    ans = 100×1 complex

  -0.0772 - 0.0867i
  -0.0751 - 0.0859i
  -0.0673 - 0.0788i
  -0.0549 - 0.0654i
  -0.0388 - 0.0469i
  -0.0200 - 0.0250i
   0.0002 - 0.0012i
   0.0208 + 0.0227i
   0.0405 + 0.0453i
   0.0587 + 0.0653i
      ⋮

    Input Arguments

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    Waveform generator object, specified as a dvbs2WaveformGenerator, dvbs2xWaveformGenerator, or ccsdsTMWaveformGenerator System object™.

    To enable the flushFilter object function when you specify obj as a ccsdsTMWaveformGenerator System object, you must set these dependencies in the ccsdsTMWaveformGenerator object.

    • Set the WaveformSource property to "synchronization and channel coding".

    • Set the ChannelCoding property to one of these values.

      • "none"

      • "RS"

      • "turbo"

      • "LDPC" — In this case, you must also set the IsLDPCOnSMTF property to 0 (false)

      • "convolutional" — In this case, you must also set the ConvolutionalCodeRate property to either "1/2" or "2/3"

      • "concatenated" — In this case, you must also set the ConvolutionalCodeRate property to either "1/2" or "2/3"

    • Set the Modulation property to either "BPSK" or "QPSK".

    Output Arguments

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    Residual data samples that remain in the filter state, returned as a column vector. The length of the column vector is equal to the product of the SamplesPerSymbol and FilterSpanInSymbols properties of the input object, obj.

    When you specify obj as dvbs2WaveformGenerator or dvbs2xWaveformGenerator System object and the NumInputStream property as a value greater than 1, the data fields generated from different input streams are merged in a round-robin technique into a single stream. The residual samples of the frame after the merging process are flushed out.

    Data Types: double
    Complex Number Support: Yes

    Version History

    Introduced in R2021a

    See Also

    Functions

    Objects