Bluetooth BR/EDR Waveform Reception Using SDR

Required Hardware

To capture signals in real time, you need ADALM-PLUTO radio and the corresponding support package add-on.

For a full list of communications toolboxes supported by SDR platforms, see the Supported Hardware section of the SDR discovery page.

Bluetooth BR/EDR Radio Specifications

Bluetooth is a short-range Wireless Personal Area Network (WPAN) technology, operating in the globally unlicensed industrial, scientific, and medical (ISM) band in the frequency range of 2.4 GHz to 2.485 GHz. In Bluetooth technology, data is divided into packets and each packet is transmitted on one of the 79 designated Bluetooth channels. Each channel has a bandwidth of 1 MHz. As there are different types of wireless networks operating in the same unlicensed frequency band, it is possible for two different networks to interfere with each other. To mitigate the interference, Bluetooth implements the frequency-hopping spread spectrum (FHSS) scheme to switch a carrier between multiple frequency channels by using a pseudorandom sequence known to both transmitter and receiver.

The Bluetooth standard specifies these physical layer (PHY) modes.

Basic rate (BR) — Mandatory mode, uses Gaussian frequency shift keying (GFSK) modulation with a data rate of 1 Mbps

Enhanced data rate (EDR) — Optional mode, uses phase shift keying (PSK) modulation with these two variants.

Bluetooth BR/EDR Packet Formats

The air interface packet formats for PHY modes include these fields:

Access Code — Each packet starts with an access code. If a packet header follows, the access code is 72 bits long. Otherwise, the length of the access code is 68 bits and referred to as a shortened access code. The access code consists of these fields:

Access Code Format

Packet Header — The header includes link control information and consists of these fields:

Header Format

Payload — Payload includes an optional payload header, a payload body, and an optional CRC. This figure shows the format of payload.

Payload Format

Guard — For EDR packets, guard time allows the Bluetooth BR/EDR radio to prepare for the change in modulation from GFSK to DPSK. The guard time must be between 4.75 to 5.25 microseconds.

Sync — For EDR packets, the synchronization sequence contains one reference symbol and ten DPSK symbols.

Trailer — For EDR packets, the trailer bits must be all zero pattern of two symbols, {00,00} for $\pi$/4-DQPSK and {000,000} for 8DPSK.

This figure shows the packet format for BR mode.

Basic Rate Packet Format

This figure shows the packet format for EDR mode.

Enhanced Data Rate Packet Format

Receiver and SDR Configuration

This figure shows the receiver procedure to decode Bluetooth BR/EDR waveform either captured by using ADALM-PLUTO or by reading IQ samples from a baseband file.

Bluetooth BR/EDR Receiver

Configure the Bluetooth BR/EDR parameters by using the bluetoothPhyConfig configuration object.

cfg = bluetoothPhyConfig;

Specify the PHY transmission mode as "BR", "EDR2M" or "EDR3M".

cfg.Mode = "BR";

Initialize the whiten initialization.

cfg.WhitenInitialization = [0;0;0;0;0;1;1];

Specify the signal source as "File" or "ADALM-PLUTO".

If you assign ADALM-PLUTO as the signal source, the example searches your computer for the ADALM-PLUTO radio at radio address 'usb:0' and uses it as the signal source.

signalSource = "File";

Specify the baseband symbol rate.

bbSymbolRate = 1e6;
if signalSource == "File"

Specify the corresponding baseband file.

    switch cfg.Mode
        case "BR"
            bbFileName = "bluetoothCapturesBR.bb";
        case "EDR2M"
            bbFileName = "bluetoothCapturesEDR2M.bb";
        case "EDR3M"
            bbFileName = "bluetoothCapturesEDR3M.bb";
    end
    sigSrc = comm.BasebandFileReader(bbFileName);
    sigSrcInfo = info(sigSrc);
    bbSampleRate = sigSrc.SampleRate;
    sigSrc.SamplesPerFrame = sigSrcInfo.NumSamplesInData;
    cfg.SamplesPerSymbol = bbSampleRate/bbSymbolRate;
else

Check if the ADALM-PLUTO hardware support package (HSP) add-on exists.

    if isempty(which("plutoradio.internal.getRootDir"))
        link = sprintf('<a href="https://www.mathworks.com/hardware-support/pluto.html">ADALM-PLUTO Radio Support From Communications Toolbox</a>');
        error("Unable to find Communications Toolbox Support Package for ADALM-PLUTO Radio. To install the support package, visit %s",link);
    end

Discover the ADALM-PLUTO radio(s) connected to your computer.

    connectedRadios = findPlutoRadio;
    radioID = connectedRadios(1).RadioID;

Specify the receiver center frequency in Hz within 2.402 GHz to 2.480 GHz.

    rxCenterFrequency = 2445000000;

Specify the base-band sample rate.

    bbSampleRate = bbSymbolRate * cfg.SamplesPerSymbol;

Create receiver System object™ for radio hardware.

    sigSrc = sdrrx("Pluto", ...
        RadioID=radioID, ...
        CenterFrequency=rxCenterFrequency, ...
        BasebandSampleRate=bbSampleRate, ...
        SamplesPerFrame=1e7, ...
        GainSource="Manual", ...
        Gain=25, ...
        OutputDataType="double");
end

Set the configuration to display the frequency spectrum of the PHY waveform.

spectrumScope = spectrumAnalyzer(Method="welch", ...
    SampleRate=bbSampleRate,...
    SpectrumType="Power density", ...
    SpectralAverages=10, ...
    YLimits=[-130 -30], ...
    Title="Received Baseband Bluetooth Signal Spectrum", ...
    YLabel="Power spectral density");

Capture Bluetooth BR/EDR Waveforms

Capture transmitted waveform as a burst.

dataCaptures = sigSrc();

Visualize the spectrum of the received Bluetooth waveform by using a spectrum analyzer.

spectrumScope(dataCaptures)

Receiver Processing

This figure shows the workflow of receiver.

Bluetooth Practical Receiver

To decode the packet header, payload header information, and raw message bits from the received baseband samples, the Bluetooth BR/EDR receiver performs these functions:

Extract the message information by using the helperBluetoothPracticalReceiver helper function.

[decBits,decodedInfo,pktStatus] = helperBluetoothPracticalReceiver(dataCaptures,cfg);

Compute the number of packets.

pktCount = length(pktStatus);
disp("Number of Bluetooth packets detected: "+num2str(pktCount))

Number of Bluetooth packets detected: 2

Enable the displayFlag flag to print the decoded packet statistics.

displayFlag = true;
if displayFlag && (pktCount~=0)
    decodedInfoPrint = decodedInfo;
    for ii = 1:pktCount
        if(pktStatus(ii))
            decodedInfoPrint(ii).PacketStatus = "Success";
        else
            decodedInfoPrint(ii).PacketStatus = "Fail";
        end
    end
    packetInfo = struct2table(decodedInfoPrint,"AsArray",1);
    fprintf("Decoded Bluetooth packet(s) information: \n \n")
    disp(packetInfo);
end

Decoded Bluetooth packet(s) information: 
 

         LAP         PacketType    LogicalTransportAddress    HeaderControlBits    PayloadLength        LLID        FlowIndicator    PacketStatus
    _____________    __________    _______________________    _________________    _____________    ____________    _____________    ____________

    {24x1 double}     {'FHS'}           {3x1 double}            {3x1 double}            18          {2x1 double}          0           "Success"  
    {24x1 double}     {'FHS'}           {3x1 double}            {3x1 double}            18          {2x1 double}          0           "Success"  

Compute the packet error rate (PER) performance metrics based on the decoded packet information.

if(pktCount)
    pktErrCount = sum(~pktStatus);
    pktErrRate = pktErrCount/pktCount;
    disp("Simulated Mode: "+cfg.Mode+", " + ...
        "Packet error rate: "+num2str(pktErrRate))
end

Simulated Mode: BR, Packet error rate: 0

Release the signal source.

release(sigSrc)

Further Exploration

You can explore and run the Bluetooth BR/EDR Waveform Generation and Transmission Using SDR example to generate and transmit a standard-compliant Bluetooth BR/EDR waveform by using the SDR. Then, use this example to demodulate and decode the BR/EDR waveform by changing the PHY transmission mode.

Troubleshooting

General tips for troubleshooting SDR hardware and the Communications Toolbox Support Package for ADALM-PLUTO Radio can be found in Common Problems and Fixes.

Appendix

This example uses this helper function:

Selected Bibliography