dvbrcs2CPMModulator

Modulate signal using CPM method specified in DVB-RCS2 standard

Since R2026a

Description

The dvbrcs2CPMModulator System object™ modulates an input signal using the continuous phase modulation (CPM) method, as specified in the Digital Video Broadcasting Second Generation Return Channel over Satellite (DVB-RCS2) standard ETSI EN 301 545-2 V1.4.1 [1]. The output is a baseband representation of the modulated signal. For more information about the modulation and filtering applied, see CPM Method and Pulse Shape Filtering.

To modulate a signal using the CPM method specified in the DVB-RCS2 standard:

Create the dvbrcs2CPMModulator object and set its properties.
Call the object with arguments, as if it were a function.

To learn more about how System objects work, see What Are System Objects?

Creation

Syntax

cpmmod = dvbrcs2CPMModulator

cpmmod = dvbrcs2CPMModulator(PropertyName=Value)

Description

cpmmod = dvbrcs2CPMModulator creates a default modulator System object that modulates a input signal using the CPM method, as specified in the DVB-RCS2 standard [1].

example

cpmmod = dvbrcs2CPMModulator(PropertyName=Value) sets properties using one or more name-value arguments. For example, dvbrcs2CPMModulator(ModulationIndex=1) sets the modulation index to 1.

Properties

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Unless otherwise indicated, properties are nontunable, which means you cannot change their values after calling the object. Objects lock when you call them, and the release function unlocks them.

If a property is tunable, you can change its value at any time.

For more information on changing property values, see System Design in MATLAB Using System Objects.

`ModulationIndex` — Modulation index
`0.5` (default) | nonnegative scalar | column vector

Modulation index, specified as a nonnegative scalar or column vector. For more information, see CPM Method.

Data Types: double

`PhaseResponseCoefficient` — Phase response coefficient
`0.98` (default) | scalar

Phase response coefficient, specified as a scalar. For more information, see Pulse Shape Filtering.

Data Types: double

`SamplesPerSymbol` — Number of samples per output symbol
`8` (default) | positive integer

Number of samples per output symbol, specified as a positive integer. This property represents the number of samples output for each integer or binary word input. For all nonbinary schemes, as defined by the pulse shapes, this value must be greater than 1.

Data Types: double

`OutputDataType` — Data type of the output
`"double"` (default) | `"single"`

Data type of the output, specified as "double" or "single".

Usage

Syntax

y = cpmmod(x)

Description

y = cpmmod(x) applies the DVB-RCS2 CPM method to the input signal, and returns the modulated baseband signal.

Input Arguments

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`x` — Input signal
column vector

Input signal, specified as a column vector of CPM input symbols. Each element of the column vector must be from the set {–3, –1, 1, 3}.

Data Types: single | double

Output Arguments

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`y` — DVB-RCS2 CPM modulated baseband signal
column vector

DVB-RCS2 CPM modulated baseband signal, returned as a column vector. The length of this output vector is equal to the number of input samples times the number of samples per symbol specified in the SamplesPerSymbol property. To specify the output data type use the OutputDataType property.

Data Types: single | double
Complex Number Support: Yes

Object Functions

To use an object function, specify the System object as the first input argument. For example, to release system resources of a System object named obj, use this syntax:

release(obj)

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Common to All System Objects

`step`	Run System object algorithm
`release`	Release resources and allow changes to System object property values and input characteristics
`clone`	Create duplicate System object
`isLocked`	Determine if System object is in use
`reset`	Reset internal states of System object

Examples

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Generate DVB-RCS2 CPM Modulated Signal

Open Live Script

Set these parameters to generate a CPM signal, as specified in the DVB-RCS2 standard.

payloadBitLen = 2052;                              % In bits
preambleLen = 64;
inpBits = randi([0 1],preambleLen+payloadBitLen,1);

Set the modulation index, samples per symbol, and phase response coefficient for the raised cosine pulse shape.

modidx = 2/5;
sps = 4;
alphaRC = 0.8;

Initialize DVB-RCS2 CPM modulator object.

modulatorObj = dvbrcs2CPMModulator(ModulationIndex=modidx, ...
    PhaseResponseCoefficient=alphaRC, ...
    SamplesPerSymbol=sps, ...
    OutputDataType="double");

Convert the input bits to CPM input symbols using gray mapping technique.

modIn = -3 + 4*(inpBits(1:2:end)) + 2*(xor(inpBits(1:2:end),inpBits(2:2:end)));

Generate DVB-RCS2 CPM modulated baseband signal.

modOut = modulatorObj(modIn);

Algorithms

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CPM Method

The output of the modulator is a baseband representation of the modulated signal:

$\begin{array}{l} s (t) = \exp [j 2 π h \sum_{i = 0}^{n} α_{i} q (t - i T_{s})], and \\ n T_{s} < t < (n + 1) T_{s} \end{array}$

where:

h is the modulation index.
{α_i} is a sequence of M-ary data symbols, which is the input to the modulator, and must be from the set {±1, ±3}. Hence, M is equal to 4.
q is the CPM phase response.

Pulse Shape Filtering

The CPM method uses pulse shaping to smooth the phase transitions of the modulated signal. DVB-RCS2 standard ETSI EN 301 545-2 V1.4.1 [1] defines the pulse shape, known as weighted average CPM pulse shape, to be a linear combination of the raised cosine and rectangular pulse shapes. The weighted average g_AV is calculated as:

g_AV(t) = α_RCg_RC(t) + (1 - α_RC)g_REC(t)

where:

α_RC is the phase response coefficient of the raised cosine pulse shape and 0 ≤ α_RC ≤ 1.
g_RC is the raised cosine phase pulse.

$g_{R C} (t) = {\begin{matrix} \frac{1}{2 L T_{s}} [1 - \cos (\frac{2 π t}{L T_{s}})], & 0 \leq t \leq L T_{s} \\ 0 & otherwise \end{matrix}$
where L is the memory of modulation and is set to L=2.
The value of (1 – α_RC) gives the phase response coefficient of the rectangular phase pulse.
For example, if α_RC = 0.75, the coefficient of the rectangular phase pulse is 0.25 = (1 – 0.75).
g_REC is the rectangular phase pulse.

$g_{R E C} (t) = {\begin{matrix} \frac{1}{2 L T_{s}}, & 0 \leq t \leq L T_{s} \\ 0 & otherwise \end{matrix}$

References

[1] ETSI Standard EN 301 545-2 V1.4.1(2024-01). Digital Video Broadcasting (DVB); Second Generation Interactive Satellite Systems (DVB-RCS2); Part-2: Lower Layers for Satellite Standard.

Extended Capabilities

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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).

Version History

Introduced in R2026a

dvbrcs2CPMModulator

Description

Creation

Syntax

Description

Properties

ModulationIndex — Modulation index 0.5 (default) | nonnegative scalar | column vector

PhaseResponseCoefficient — Phase response coefficient 0.98 (default) | scalar

SamplesPerSymbol — Number of samples per output symbol 8 (default) | positive integer

OutputDataType — Data type of the output "double" (default) | "single"

Usage

Syntax

Description

Input Arguments

x — Input signal column vector

Output Arguments

y — DVB-RCS2 CPM modulated baseband signal column vector

Object Functions

Common to All System Objects

Examples

Generate DVB-RCS2 CPM Modulated Signal

Algorithms

CPM Method

Pulse Shape Filtering

References

Extended Capabilities

C/C++ Code Generation Generate C and C++ code using MATLAB® Coder™.

Version History

See Also

`ModulationIndex` — Modulation index
`0.5` (default) | nonnegative scalar | column vector

`PhaseResponseCoefficient` — Phase response coefficient
`0.98` (default) | scalar

`SamplesPerSymbol` — Number of samples per output symbol
`8` (default) | positive integer

`OutputDataType` — Data type of the output
`"double"` (default) | `"single"`

`x` — Input signal
column vector

`y` — DVB-RCS2 CPM modulated baseband signal
column vector

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.