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Bluetooth BR/EDR Waveform Reception by Using SDR

This example shows how to capture and decode Bluetooth BR/EDR waveforms by using the Communications Toolbox™ Library for the Bluetooth Protocol. You can either capture the Bluetooth BR/EDR waveforms by using the ADALM-PLUTO radio or load IQ samples corresponding to the Bluetooth BR/EDR waveforms from a baseband file (*.bb). To generate and transmit the Bluetooth BR/EDR waveforms, refer to Bluetooth BR/EDR Waveform Generation and Transmission using SDR and configure your test environment with:

  • Two SDR platforms connected to the same host computer, and run two MATLAB® sessions on the single host computer.

  • Two SDR platforms connected to two host computers, and run one MATLAB session on each host computer.

To configure your host computer to work with the Support Package for ADALM-PLUTO Radio, refer to Guided Host-Radio Hardware Setup (Communications Toolbox Support Package for Analog Devices ADALM-Pluto Radio).

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, refer to the Supported Hardware section of the Software Defined Radio (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:

  • EDR2M: Uses pi/4-DQPSK with a data rate of 2 Mbps

  • EDR3M: Uses 8-DPSK with a data rate of 3 Mbps

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:

  • Preamble: The preamble is a fixed zero-one pattern of four symbols.

  • Sync Word: The sync word is a 64-bit code word derived from the 24-bit lower address part (LAP) of the Bluetooth device address.

  • Trailer: The trailer is a fixed zero-one pattern of four symbols.

Access Code Format

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

  • LT_ADDR: 3-bit logical transport address

  • TYPE: 4-bit type code, which specifies the packet type used for transmission. The value of this field can be ID, NULL, POLL, FHS, HV1, HV2, HV3, DV, EV3, EV4, EV5, 2-EV3, 2-EV5, 3-EV3, 3-EV5, DM1, DH1, DM3, DH3, DM5, DH5, AUX1, 2-DH1, 2-DH3, 2-DH5, 3-DH1, 3-DH3 and 3-DH5. This field determines the number of slots the current packet occupies.

  • FLOW: 1-bit flow control over the asynchronous connection-oriented logical (ACL) transport

  • ARQN: 1-bit acknowledgement indication

  • SEQN: 1-bit sequence number

  • HEC: 8-bit header error check

Header Format

Payload: Payload includes an optional payload header, a payload body, and an optional CRC.

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.

Packet format for BR mode is shown in this figure.

Basic Rate Packet Format

Packet format for EDR mode is shown in this figure.

Enhanced Data Rate Packet Format

Check for Support Package Installation

Check if the Communications Toolbox Library for the Bluetooth Protocol support package is installed.

commSupportPackageCheck('BLUETOOTH');

Decode Bluetooth BR/EDR Waveforms

This example shows how to decode Bluetooth BR/EDR waveforms either captured by using ADALM-PLUTO or by reading IQ samples from a baseband file.

Bluetooth BR/EDR Receiver

The general structure of the Bluetooth receiver example is:

  1. Initialize the receiver parameters.

  2. Specify the signal source.

  3. Capture the Bluetooth BR/EDR waveforms.

  4. Process Bluetooth BR/EDR waveforms at receiver.

Initialize the Receiver Parameters

To configure Bluetooth BR/EDR parameters, use bluetoothPhyConfig object.

cfg = bluetoothPhyConfig;
cfg.Mode = 'BR'; % Mode of transmission as one of BR, EDR2M and EDR3M
cfg.WhitenInitialization = [0;0;0;0;0;1;1]; % Whiten initialization

Specify the Signal Source

Specify the signal source as File or ADALM-PLUTO.

  • File: Uses the comm.BasebandFileReader to read a file that contains a previously captured over-the-air signal.

  • ADALM-PLUTO: Uses thesdrrx (Communications Toolbox Support Package for Analog Devices ADALM-Pluto Radio) System object to receive a live signal from the SDR hardware.

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.

% The default signal source is 'File'
signalSource = 'File';

bbSymbolRate = 1e6; % 1 MSps
if strcmp(signalSource,'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 pluto Hardware Support Package (HSP) is installed
    if isempty(which('plutoradio.internal.getRootDir'))
        error(message('comm_demos:common:NoSupportPackage', ...
                      'Communications Toolbox Support Package for ADALM-PLUTO Radio',...
                      ['<a href="https://www.mathworks.com/hardware-support/' ...
                      'adalm-pluto-radio.html">ADALM-PLUTO Radio Support From Communications Toolbox</a>']));
    end
    connectedRadios = findPlutoRadio; % Discover ADALM-PLUTO radio(s) connected to your computer
    radioID = connectedRadios(1).RadioID;    
    rxCenterFrequency = 2445000000;  % In Hz, choose between 2.402e9 to 2.480e9 with 1e6 spacing
    bbSampleRate = bbSymbolRate * cfg.SamplesPerSymbol;
    sigSrc = sdrrx('Pluto',...
        'RadioID',             radioID,...
        'CenterFrequency',     rxCenterFrequency,...
        'BasebandSampleRate',  bbSampleRate,...
        'SamplesPerFrame',     1e7,...
        'GainSource',         'Manual',...
        'Gain',                25,...
        'OutputDataType',     'double');
end

Capture the Bluetooth BR/EDR Waveforms

Capture the IQ samples corresponding to Bluetooth BR/EDR waveforms either by using ADALM-PLUTO or baseband file as signal source. Visualize the spectrum of the received Bluetooth waveforms by using a spectrum analyzer.

% The transmitted waveforms are captured as a burst
dataCaptures = sigSrc();

% Setup spectrum viewer
spectrumScope = dsp.SpectrumAnalyzer( ...
    'SampleRate',       bbSampleRate,...
    'SpectrumType',     'Power density', ...
    'SpectralAverages', 10, ...
    'YLimits',          [-130 -30], ...
    'Title',            'Received Baseband Bluetooth Signal Spectrum', ...
    'YLabel',           'Power spectral density');

% Show power spectral density of the received waveform
spectrumScope(dataCaptures);

Process Bluetooth BR/EDR Waveforms at Receiver

To decode the packet header, payload header information, and raw message bits, the receiver processess the baseband samples received from the signal source. This figure shows the receiver processing.

Bluetooth Practical Receiver

The Bluetooth practical receiver performs these functions:

  1. Remove DC offset 

  2. Detect the signal bursts  

  3. Perform matched filtering 

  4. Estimate and correct the timing offset 

  5. Estimate and correct the carrier frequency offset 

  6. Demodulate BR/EDR waveform 

  7. Perform forward error correction (FEC) decoding 

  8. Perform data dewhitening 

  9. Perform header error check (HEC) and cyclic redundancy check (CRC) 

  10. Outputs decoded bits and decoded packet statistics based on decoded lower address part (LAP), HEC and CRC 

% Bluetooth practical receiver
[decBits,decodedInfo,pktStatus] = helperBluetoothPracticalReceiver(dataCaptures,cfg);

% Get the number of detected packets
pktCount = length(pktStatus);
disp(['Number of Bluetooth packets detected: ' num2str(pktCount)])
Number of Bluetooth packets detected: 2
% Get the decoded packet statistics
displayFlag = true; % set true, to display the decoded packet statistics  
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'} 
% Get the packet error rate performance metrics
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);

This example enables you to decode Bluetooth BR/EDR waveforms either captured by using ADALM-PLUTO or by reading IQ samples from a baseband file. Visualize the spectrum of the received Bluetooth waveforms by using a spectrum analyzer. The packet error rate is computed based on the decoded packet information.

Further Exploration

You can use this example to receive EDR packets by changing the PHY transmission mode. To generate the Bluetooth waveforms in this example, refer to Bluetooth BR/EDR Waveform Generation and Transmission using SDR.

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 (Communications Toolbox Support Package for Analog Devices ADALM-Pluto Radio).

Appendix

This example uses this helper function:

Selected Bibliography

  1. Bluetooth Special Interest Group (SIG). "Core System Package [BR/EDR Controller Volume]". Bluetooth Core Specification. Version 5.1, Volume 2 <https://www.bluetooth.com/>