comm.RBDSWaveformGenerator

Generate RDS/RBDS waveform

Description

The comm.RBDSWaveformGenerator System object™ generates configurable standard-compliant baseband RDS/RBDS waveforms in MATLAB^®. RDS/RBDS waveforms supplement FM radio stations with additional textual information, such as song title, artist name, and station description. The RDS/RBDS signal lies in the 57-kHz band of the baseband FM radio signal.

Use this object to generate a waveform containing RadioText Plus (RT+) information and register a custom encoding implementation for an Open Data Application (ODA). You can also specify the time, data, and the program type. The object supports short, scrolling 8-character text, and longer 32-character or 64-character text.

To generate baseband RDS/RBDS waveforms:

1. Create a comm.RBDSWaveformGenerator object and set the properties of the object.

2. Call step to generate the waveform.

Note

Alternatively, instead of using the step method to perform the operation defined by the System object, you can call the object with arguments, as if it were a function. For example, y = step(obj,x) and y = obj(x) perform equivalent operations.

Construction

rbdsgen = comm.RBDSWaveformGenerator creates an RDS/RBDS waveform generator object, rbdsgen, using the default properties.

rbdsgen = comm.RBDSWaveformGenerator(Name,Value) specifies additional properties using Name,Value pairs. Unspecified properties have default values.

Example:

rbdsgen = comm.RBDSWaveformGenerator( ...
     'GroupsPerFrame',20,'SamplesPerSymbol',10, ...
     'SendRadioTextPlus',true);

Properties

If a property is listed as tunable, then you can change its value even when the object is locked.

SamplesPerSymbol — Number of samples per symbol

10 (default) | positive even integer

Number of samples per symbol (bit), specified as a positive even integer. Half of the samples represent one amplitude level of Manchester coding. The other half of the samples represent the opposite level.

GroupsPerFrame — Number of groups per output frame

10 (default) | scalar integer

Number of groups per output frame, specified as a scalar integer. Each group is 104 symbols (bits) long.

RadioText — Long text conveyed with type 2A groups

'Long text' (default) | character vector

Radio text conveyed with type 2A groups, specified as a character vector that is up to 64 characters long. The object transmits the specified text four characters at a time, using type 2A groups.

Tunable: Yes

ProgramServiceName — Label of the program service

'ShortTxt' (default) | character vector

Label of the program service, specified as a character vector that is up to eight characters long. This information is conveyed as a short text with type 0A groups, two characters at a time.

Tunable: Yes

ProgramIdentificationCode — Program identification code

[0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0] (default) | 16-bit row vector

Program identification (PI) code, specified as a 16-bit row vector. In North America, the PI code conveys the call letters of the station. Example call letters include 'WABC' and 'KXYZ'.

To generate North American PI codes for a station's call letters, use the callLettersToPICode method.

ProgramType — Program type

'No program type or undefined' (default) | character vector

Program type, specified as a character vector containing one of the 31 values allowed by the RDS/RBDS standard. For a list of program types that the RDS/RBDS standard allows in North America, see [1].

Tunable: Yes

ProgramTypeName — Program type name

'' (default) | character vector

Program type name, specified as a character vector that is up to eight characters long. This text further characterizes the program type, such as 'Football' for the program type 'Sports'. The object conveys the program type name using type 10A groups. If this property is empty, then no 10A groups are generated.

Tunable: Yes

SendDateTime — Option to advertise date and time

false (default) | true

Option to advertise the date and time, specified as either false or true. When you set this property to true, one 4A group is periodically generated every 685 groups (once a minute).

AlternativeFrequencies — Alternative frequencies

[] (default) | row vector

Alternative frequencies, specified as a row vector in MHz. This information is conveyed with type 0A groups. It indicates other transmitters broadcasting the same program in the same or adjacent reception areas. With this information, receivers can switch to a different frequency with better reception.

SendRadioTextPlus — Option to send RT+ information

false (default) | true

Option to transmit RadioText Plus (RT+) information, specified as a scalar logical. When you set this property to true, the RT+ ODA information is advertised with type 3A groups. In addition, the RT+ content types, specified in RadioTextType1, RadioTextType2, and the two RT+ substrings indexed by RadioTextIndices are conveyed with the open-format type 11A group.

RadioTextType1 — Content type of first RT+ substring

'Item.Artist' (default) | character vector

Content type of the first RT+ substring, specified as a character vector. Allowed values are the class names specified in the RT+ standard. For more details, see [2].

Tunable: Yes

RadioTextType2 — Content type of second RT+ substring

'Item.Title' (default) | character vector

Content type of the second RT+ substring, specified as a character vector. Allowed values are the class names specified in the RT+ standard. For more details, see [2].

Tunable: Yes

RadioTextIndices — Start and end indices of RT+ substrings

[1 2; 3 4] (default) | 2-by-2 matrix of positive integers

Start and end indices of RT+ substrings, specified as a 2-by-2 matrix of positive integers. The first column indexes the beginning of each RT+ substring. The second column indexes the end of each substring.

Tunable: Yes

Methods

callLettersToPICode	Convert North-American call letters to binary PI code
registerODA	Register a custom encoding implementation for an ODA
step	Generate RDS/RBDS waveform

Common to All System Objects
release	Allow System object property value changes
reset	Reset internal states of System object

Examples

Generate a Basic RBDS Waveform

Generate a basic RBDS waveform, FM modulate the waveform with an audio signal, and then demodulate the waveform.

Each frame of the RBDS waveform contains 19 groups, with a group length of 104 bits (symbols) each. Set the number of samples per RBDS symbol to 10. Therefore, the number of samples in each frame of RBDS waveform is 104 x 10 x 19 = 19,760. According to the RBDS standard, the bit rate is 1187.5 Hz. So, the RBDS sample rate = 1187.5 x samples per RBDS symbol. Set the audio frame rate to 40 x 1187.5 = 47,500.

groupLen = 104;
sps = 10;
groupsPerFrame = 19;
rbdsFrameLen = groupLen*sps*groupsPerFrame;
afrRate = 40*1187.5;
rbdsRate = 1187.5*sps;
outRate = 4*57000;

afr = dsp.AudioFileReader( ...
    "rbds_capture_47500.wav", ...
    SamplesPerFrame=rbdsFrameLen*afrRate/rbdsRate);
rbds = comm.RBDSWaveformGenerator( ...
    GroupsPerFrame=groupsPerFrame, ...
    SamplesPerSymbol=sps);

fmMod = comm.FMBroadcastModulator( ...
    AudioSampleRate=afr.SampleRate, ...
    SampleRate=outRate,...
    Stereo=true, ...
    RBDS=true, ...
    RBDSSamplesPerSymbol=sps);
fmDemod = comm.FMBroadcastDemodulator( ...
    SampleRate=outRate,...
    Stereo=true, ...
    RBDS=true, ...
    PlaySound=true);
scope = timescope(SampleRate=outRate,YLimits=10^-2*[-1 1]);

Get the audio input and generate the RBDS waveform. FM modulate the stereo audio with the RBDS waveform, add noise, and FM demodulate the audio and RBDS waveforms. View the demodulated RBDS waveform in the time scope.

for idx = 1:7
    % Get current audio input
    input = afr();              
    % Generate RBDS info at the same configured rate
    rbdsWave = rbds();
    % FM modulate stereo audio with RBDS info
    yFM = fmMod( ...
        [input input], ...
        rbdsWave);
    % Add noise
    rcv = awgn(yFM, 40);
    % FM demodulate the audio and RBDS waveforms
    [audioRcv, rbdsRcv] = fmDemod(rcv);
    scope(rbdsRcv);
end
release(scope)

Generate RBDS Waveform with RadioText Plus Information

Create a comm.RBDSWaveformGenerator System object™ with 20 groups per frame and 10 samples per symbol. Add the Radio Text plus (RT+) information, such as artist name and song, title, to the waveform. Indicate the start and end of the RT+ substrings by using the RadioTextIndices property.

rbds = comm.RBDSWaveformGenerator('GroupsPerFrame',20,'SamplesPerSymbol',10,...
    'SendRadioTextPlus', true);
rbds.RadioText = 'MyArtist - MySongTitle';
rbds.RadioTextType1 = 'Item.Artist';
rbds.RadioTextType2 = 'Item.Title';
rbds.RadioTextIndices = [1 8; 12 22]; 
for idx = 1:10
    rbds.step();
end

Register a Custom Encoding Implementation

Register a custom encoding implementation for an Open Data Application (ODA) by using the registerODA method of the comm.RBDSWaveformGenerator System object™. Set the ODA ID to 'CD46', which is the ID for the traffic message channel. The allocated group type is 8A.

rbds = comm.RBDSWaveformGenerator();
odaID = 'CD46';
allocatedGroupType = '8A';

This example uses the following templates as a starting point for custom encoding implementation.

mainProcessingFcn = @CustomODAEncodingMain;
fcn3A             = @CustomODAEncoding3A;
registerODA(rbds,odaID,allocatedGroupType,mainProcessingFcn,fcn3A);
s = info(rbds);
s.ODAMap

ans=2×1 struct array with fields:
    ID
    GroupType
    FunctionMain
    Function3A

Configure RBDS Waveforms with Date and Time Information

Generate RBDS waveform with date and time information, the program type, and alternative frequencies. The comm.RBDSWaveformGenerator object uses type 4A groups for date and time information, type 10A groups for the program type information, and type 0A groups for alternative frequencies. View the waveform in a spectrum analyzer.

rbds = comm.RBDSWaveformGenerator( ...
    GroupsPerFrame=1000);
sa = spectrumAnalyzer( ...
    SampleRate=1187.5*rbds.SamplesPerSymbol, ...
    YLimits=[-140 20]);
rbds.SendDateTime = true;          % send type 4A groups
rbds.ProgramType = "Sports";
rbds.ProgramTypeName = "Football"; % send type 10A groups
rbds.AlternativeFrequencies = ...  % info sent in type 0A groups
    [99.1 102.5];
wave = rbds();
sa(wave)
release(sa)

Algorithms

comm.RBDSWaveformGenerator generates waveforms according to the RDS/RBDS standard [1]. The RDS/RBDS standard consists of three layers: physical layer, data-link layer, and session and application layer.

Physical Layer

The physical layer (first layer) converts the data-link bits to an analog waveform by conducting differential encoding and biphase symbol encoding (Manchester encoding) and pulse-shaping filtering.

Data-Link Layer

The data-link layer (second layer) performs (26,16) cyclic encoding shortened from (341,331) encoding [1]. The second layer is responsible for error detection, error correction, and the establishment of group-level synchronization. Each group of RDS/RBDS frames contains four blocks of 26 bits (that is 104 bits) each. Each block contains an information word and a check word. Each information word contains 16 bits, and each check word contains 10 bits.

Here is the baseband coding structure for the RDS/RBDS waveform. For more details, see [1].

For each block, a unique offset word is modulo-2 added to the checkword bits. The added offset word provides a group and block synchronization system in the receiver (decoder). Because the addition of the offset is reversible in the decoder, the normal additive error-correcting and detecting properties of the basic code are unaffected.

Session and Application Layer

The first block in every group contains a program identification (PI) code. The first four bits of the second block of every group are allocated to a four-bit code. This code specifies the application of the group. Groups are referred to as types 0–15 according to the binary weighting A₃ = 8, A₂ = 4, A₁ = 2, A₀ = 1. The fifth bit of the second block, B₀, defines the version of the application. If B₀ = 0, the version of the group is A. The PI code in this version is inserted into block 1 only. Example group types include 0A, 1A, 2A, 3A, and 4A.

The Program Type code and Traffic Program Identification (PI) occupy fixed locations in block 2 of every group.

Group Types

References

[1] National Radio Systems Committee. United States RBDS Standard: Specification of the radio broadcast data system (RBDS). Electronic Industries Association and National Association of Broadcasters. April 9, 1998.

[2] Westdeutscher Rundfunk WDR, Nokia, and Institut für Rundfunktechnik IRT. RadioText Plus (RT+) Specification, Version 2.1. 2006.

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

See System Objects in MATLAB Code Generation (MATLAB Coder).

In addition, the following limitations apply when you generate code that contains this System object or when you use this object in a MATLAB function block.

• The group type 4A cannot be transmitted in the generated code.

• The registerODA method is not supported.

• The ProgramType property is not tunable.

Version History

Introduced in R2017a