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DVB-S2 Transmitter Using Software-Defined Radio

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This example shows how to generate Digital Video Broadcasting Satellite Second Generation (DVB-S2) physical layer (PL) frames and transmit them over-the-air using a software-defined radio (SDR) device or store them in a file. You can decode the PL frames using the DVB-S2 Receiver Using Software-Defined Radio example with an additional SDR hardware device.

Introduction

For this example, use a dvbs2WaveformGenerator System object™ to generate a DVB-S2 baseband waveform configured to the specified parameters. Transmit the generated waveform over-the-air using the SDRu transmitter System object and SDR hardware.

This example supports these SDRs.

  • ADALM-PLUTO (requires Communications Toolbox™ Support Package for Analog Devices® ADALM-PLUTO Radio)

  • USRP™ B200/B210/N200/N210/USRP2 (requires Communications Toolbox Support Package for USRP™ Radio)

The SDR device in this setup transmits DVB-S2 in-phase and quadrature phase (IQ) samples at the specified frequency and a symbol rate of 1 Msps.

This diagram summarizes the transmission process.

dvb1.png

Download DVB-S2 LDPC Parity Matrices Data Set

Load a MAT file containing DVB-S2 LDPC parity matrices. If the MAT file is not available on the MATLAB® path, use these commands to download and unzip the MAT file.

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

Example Setup

You can write the DVB-S2 waveform to a file or transmit it using an SDR platform. To transmit the waveform using an SDR platform, set useSDR to true.

useSDR = false;

If you set useSDR to true, configure the variables required for SDR transmission.

if useSDR
    txsim.DeviceName = "B200";
    txsim.RadioCenterFrequency = 915e6;
    txsim.RadioGain = 25;
end

DVB-S2 Configuration Setup

Initialize a dvbs2WaveformGenerator System object and set its properties.

wg = dvbs2WaveformGenerator;
wg.FECFrame = "short";
wg.MODCOD = 24;                               % 32APSK 3/4
wg.DFL = getDFL(wg.MODCOD,wg.FECFrame);       % Default DFL is Kbch-80
wg.SamplesPerSymbol = 2
wg = 
  dvbs2WaveformGenerator with properties:

           StreamFormat: "TS"
        NumInputStreams: 1
               FECFrame: "short"
                 MODCOD: 24
                    DFL: 11632
          ScalingMethod: "outer radius as 1"
              HasPilots: 0
          RolloffFactor: 0.3500
    FilterSpanInSymbols: 10
       SamplesPerSymbol: 2

  Show all properties

Generate Input Data

Generate input data in the form of packets, with the first byte being the sync byte. Concatenate multiple packets to create a frame of DFL length. Generate 50 frames.

numFrames = 50;                                           % Number of PL frames to be processed
rng("default")
if strcmpi(wg.StreamFormat,"TS")
    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
else
    if wg.UPL
        syncBits = randi([0 1],8,1);
        pktLen = wg.UPL - 8;                              % UP length without sync byte
    end
end
% For GS continuous streams
if strcmpi(wg.StreamFormat,"GS") && wg.UPL == 0
    numBits = wg.DFL*numFrames;
    data = randi([0 1],numBits,1);
else % For TS and GS packetized streams
    numPkts = wg.MinNumPackets*numFrames;
    txRawPkts = randi([0 1],pktLen,numPkts);
    txPkts = [repmat(syncBits,1,numPkts); txRawPkts];
    data = txPkts(:);
end

Generate DVB-S2 Waveform

Generate DVB-S2 baseband waveform in pilot-aided mode.

wg.HasPilots = true;
txOut = [wg(data); flushFilter(wg)];

Configure SDR for Transmission

Discover radio(s) connected to your computer. This example uses the first SDR radio found using the txsim.DeviceName and findsdru function. Check if the radio is available and record the radio type. Initialize sdrtx or comm.SDRuTransmitter System object. Set the platform, center frequency, sample rate, gain, and other relevant properties. Transmit the DVB-S2 waveform over-the-air using SDR device.

Rsym = 1e6;
Fsamp = Rsym*wg.SamplesPerSymbol;                                                % Sampling rate in samples per second
if useSDR
    if matches(txsim.DeviceName,"Pluto")
        frameSize = getFrameSize(wg.FECFrame,wg.MODCOD)*wg.SamplesPerSymbol;
        radioTx = sdrtx("Pluto");
        radioTx.RadioID               = "usb:1";
        radioTx.CenterFrequency       = txsim.RadioCenterFrequency;
        radioTx.BasebandSampleRate    = Fsamp;
        radioTx.SamplesPerFrame       = frameSize;
        radioTx.Gain                  = txsim.RadioGain;
    else
        connectedRadios = findsdru;
        rIdx = find(strcmp(txsim.DeviceName,{connectedRadios.Platform}));
        if strcmp(connectedRadios(rIdx).Status,"Success")
            usrpTx.Platform = connectedRadios(rIdx).Platform;
            switch usrpTx.Platform
                case {'B200','B210'}
                    usrpTx.SerialNum = connectedRadios(rIdx).SerialNum;
                    usrpTx.MasterClockRate = 20e6;
                case 'N200/N210/USRP2'
                    usrpTx.Address = connectedRadios(rIdx).IPAddress;
                    usrpTx.MasterClockRate = 100e6;
                otherwise
                    error("%s\n","Unsupported USRP device")
            end
        end
        usrpTx.Gain = txsim.RadioGain;                                            % In dB
        switch usrpTx.Platform
            case {'B200','B210'}
                radioTx = comm.SDRuTransmitter( ...
                    Platform             = usrpTx.Platform, ...
                    SerialNum            = usrpTx.SerialNum, ...
                    CenterFrequency      = txsim.RadioCenterFrequency, ...
                    MasterClockRate      = usrpTx.MasterClockRate, ...
                    InterpolationFactor  = usrpTx.MasterClockRate/Fsamp, ...
                    Gain                 = usrpTx.Gain);
            case 'N200/N210/USRP2'
                radioTx = comm.SDRuTransmitter(...
                    Platform            = usrpTx.Platform, ...
                    IPAddress           = usrpTx.Address, ...
                    CenterFrequency     = txsim.RadioCenterFrequency, ...
                    Gain                = usrpTx.Gain, ...
                    InterpolationFactor = usrpTx.MasterClockRate/Fsamp);
        end
    end
    numRepeatTxFrames = 1000;                                                     % Waveform is repeatedly transmitted in a loop
    disp(radioTx)
    fprintf("Starting transmission at Fs = %g MHz\n",Fsamp/1e6)
    for frame = 1:numRepeatTxFrames
        underrun = radioTx(txOut);
        if (underrun) 
            warning("Dropped samples.")
        end
    end
    fprintf("Transmission finished\n")
    release(radioTx)

Save Waveform to File

Save the waveform in a MAT file.

else
    fprintf("Writing DVB-S2 IQ samples into a file\n")
    filename = "dvbs2ModCod" + string(wg.MODCOD) + "Waveform.mat";
    save(filename,'txOut')
end
Writing DVB-S2 IQ samples into a file

release(wg)

Further Exploration

The companion example DVB-S2 Receiver Using Software-Defined Radio example can be used to decode the waveform transmitted by this example.

SDR Troubleshooting

References

  1. ETSI Standard EN 302 307-1 V1.4.1(2014-11). Digital Video Broadcasting (DVB); Second Generation Framing Structure, Channel Coding and Modulation Systems for Broadcasting, Interactive Services, News Gathering and other Broadband Satellite Applications (DVB-S2).

Local Functions

function dfl = getDFL(modCod,fecFrame)
% Get data field length
if strcmp(fecFrame,"normal")
    nDefVal = [16008 21408 25728 32208 38688 43040 48408 51648 53840 57472 ...
        58192 38688 43040 48408 53840 57472 58192 43040 48408 51648 53840 ...
        57472 58192 48408 51648 53840 57472 58192] - 80;
else
    nDefVal = [3072 5232 6312 7032 9552 10632 11712 12432 13152 14232 0 ...
        9552 10632 11712 13152 14232 0 10632 11712 12432 13152 14232 0 11712 ...
        12432 13152 14232 0] - 80;
end
dfl = nDefVal(modCod);
end
function frameSize = getFrameSize(fecFrame,modCod)
% Get PL frame size
[modOrder,~,cwLen] = satcom.internal.dvbs.getS2PHYParams(modCod,fecFrame);
dataLen = cwLen/log2(modOrder);
% Pilot sequence and indices generation
slotLen = 90;
pilotBlkFreq = 16;                                                              % In slots
numPilotBlks = floor(dataLen/(slotLen*pilotBlkFreq));
if floor(dataLen/(slotLen*16)) == dataLen/(slotLen*pilotBlkFreq)
    numPilotBlks = numPilotBlks - 1;
end
pilotLen = numPilotBlks*36;                                                     % One pilot block contains 36 pilot symbols
frameSize = dataLen + pilotLen + slotLen;
end

See Also

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