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Bluetooth LE Waveform Generation and Transmission Using SDR

This example shows how to implement a Bluetooth® Low Energy (LE) transmitter using the Bluetooth® Library. You can either transmit Bluetooth LE signals using the ADALM-PLUTO radio or write to a baseband file (*.bb). The transmitted Bluetooth LE signal can be received by the companion example, Bluetooth LE Waveform Reception Using SDR, with any one of the following setup: (i) Two SDR platforms connected to the same host computer which runs two MATLAB sessions (ii) Two SDR platforms connected to two computers which run separate MATLAB sessions.

Refer to the Guided Host-Radio Hardware Setup documentation for details on how to configure your host computer to work with the Support Package for ADALM-PLUTO Radio.

Required Hardware and Software

To transmit signals in real time, you need ADALM-PLUTO radio and the corresponding support package Add-On:

For a full list of Communications Toolbox supported SDR platforms, refer to Supported Hardware section of the Software Defined Radio (SDR) discovery page.


The Bluetooth Special Interest Group (SIG) introduced Bluetooth LE for low power short range communications. The Bluetooth standard specifies the Link layer which includes both PHY and MAC layers. Bluetooth LE applications include image and video file transfers between mobile phones, home automation, and the Internet of Things (IoT).

Specifications of Bluetooth LE:

  • Transmission frequency range: 2.4-2.4835 GHz

  • RF channels : 40

  • Symbol rate : 1 Msym/s, 2 Msym/s

  • Modulation : Gaussian Minimum Shift Keying (GMSK)

  • PHY transmission modes : (i) LE1M - Uncoded PHY with data rate of 1 Mbps (ii) LE2M - Uncoded PHY with data rate of 2 Mbps (iii) LE500K - Coded PHY with data rate of 500 Kbps (iv) LE125K - Coded PHY with data rate of 125 Kbps

The Bluetooth standard specifies air interface packet formats for all the four PHY transmission modes of Bluetooth LE using the following fields:

  • Preamble: The preamble depends on PHY transmission mode. LE1M mode uses an 8-bit sequence of alternate zeros and ones, '01010101'. LE2M uses a 16-bit sequence of alternate zeros and ones, '0101...'. LE500K and LE125K modes use an 80-bit sequence of zeros and ones obtained by repeating '00111100' ten times.

  • Access Address: Specifies the connection address shared between two Bluetooth LE devices using a 32-bit sequence.

  • Coding Indicator: 2-bit sequence used for differentiating coded modes (LE125K and LE500K).

  • Payload: Input message bits including both protocol data unit (PDU) and cyclic redundancy check (CRC). The maximum message size is 2080 bits.

  • Termination Fields: Two 3-bit vectors of zeros, used in forward error correction encoding. The termination fields are present for coded modes (LE500K and LE125K) only.

Packet format for uncoded PHY (LE1M and LE2M) modes is shown in the figure below:

Packet format for coded PHY (LE500K and LE125K) modes is shown in the figure below:

Example Structure

The general structure of the Bluetooth LE transmitter example is described as follows:

  1. Generate link layer PDUs

  2. Generate baseband IQ waveforms

  3. Transmitter processing

Generate Link Layer PDUs

Link layer PDUs can be either advertising channel PDUs or data channel PDUs. You can configure and generate advertising channel PDUs using bleLLAdvertisingChannelPDUConfig and bleLLAdvertisingChannelPDU functions respectively. You can configure and generate data channel PDUs using bleLLDataChannelPDUConfig and bleLLAdvertisingChannelPDUDecode functions respectively.

% Configure an advertising channel PDU
cfgLLAdv = bleLLAdvertisingChannelPDUConfig;
cfgLLAdv.PDUType         = 'Advertising indication';
cfgLLAdv.AdvertisingData = '0123456789ABCDEF';
cfgLLAdv.AdvertiserAddress = '1234567890AB';

% Generate an advertising channel PDU
messageBits = bleLLAdvertisingChannelPDU(cfgLLAdv);

Generate Baseband IQ Waveforms

You can use the bleWaveformGenerator function to generate standard-compliant waveforms.

phyMode = 'LE1M'; % Select one mode from the set {'LE1M','LE2M','LE500K','LE125K'}
sps = 8;          % Samples per symbol
channelIndex = 37;  % Channel index value in the range [0,39]
accessAddressLen = 32;% Length of access address
accessAddressHex = '8E89BED6';  % Access address value in hexadecimal
accessAddressBin = int2bit(hex2dec(accessAddressHex),accessAddressLen,false); % Access address in binary

% Symbol rate based on |'Mode'|
symbolRate = 1e6;
if strcmp(phyMode,'LE2M')
    symbolRate = 2e6;

% Generate Bluetooth LE waveform
txWaveform = bleWaveformGenerator(messageBits,...
    'Mode',            phyMode,...
    'ChannelIndex',    channelIndex,...
    'AccessAddress',   accessAddressBin);

% Set up spectrum viewer
spectrumScope = spectrumAnalyzer('Method','welch', ...
    'SampleRate',       symbolRate*sps,...
    'SpectrumType',     'Power density', ...
    'SpectralAverages', 10, ...
    'YLimits',          [-130 0], ...
    'Title',            'Baseband Bluetooth LE Signal Spectrum', ...
    'YLabel',           'Power spectral density');

% Show power spectral density of the Bluetooth LE signal

Transmitter Processing

Specify the signal sink as 'File' or 'ADALM-PLUTO'.

  • File:Uses the comm.BasebandFileWriter to write a baseband file.

  • ADALM-PLUTO: Uses the sdrtx System object to transmit a live signal from the SDR hardware.

% Initialize the parameters required for signal source
txCenterFrequency       = 2.402e9;  % Varies based on channel index value
txFrameLength           = length(txWaveform);
txNumberOfFrames        = 1e4;
txFrontEndSampleRate    = symbolRate*sps;

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

if strcmp(signalSink,'File')

    sigSink = comm.BasebandFileWriter('CenterFrequency',txCenterFrequency,...
    sigSink(txWaveform); % Writing to a baseband file ''

elseif strcmp(signalSink,'ADALM-PLUTO')

    % First check if the HSP exists
    if isempty(which('plutoradio.internal.getRootDir'))
		link = sprintf('<a href=""> 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);
    connectedRadios = findPlutoRadio; % Discover ADALM-PLUTO radio(s) connected to your computer
    radioID = connectedRadios(1).RadioID;
    sigSink = sdrtx( 'Pluto',...
        'RadioID',           radioID,...
        'CenterFrequency',   txCenterFrequency,...
        'Gain',              0,...
        'SamplesPerFrame',   txFrameLength,...
    % The transfer of baseband data to the SDR hardware is enclosed in a
    % try/catch block. This means that if an error occurs during the
    % transmission, the hardware resources used by the SDR System
    % object(TM) are released.
    currentFrame = 1;
        while currentFrame <= txNumberOfFrames
            % Data transmission
            % Update the counter
            currentFrame = currentFrame + 1;
    catch ME
    error('Invalid signal sink. Valid entries are File and ADALM-PLUTO.');

% Release the signal sink

Further Exploration

The companion example Bluetooth LE Waveform Reception Using SDR can be used to decode the waveform transmitted by this example. You can also use this example to transmit the data channel PDUs by changing channel index, access address and center frequency values in both the examples.


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

Selected Bibliography

  1. Bluetooth Technology Website | The Official Website of Bluetooth Technology, Accessed November 22, 2021.

  2. Volume 6 of the Bluetooth Core Specification, Version 5.3 Core System Package [Low Energy Controller Volume].

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