comm.SOQPSKModulator

Modulate signal using SOQPSK method

Since R2026a

Description

The comm.SOQPSKModulator System object™ modulates an input signal by using the shaped-offset quadrature phase shift keying (SOQPSK) method. The output is a baseband representation of the modulated signal. For more information about the modulation and filtering applied, see Algorithms.

To modulate a signal using the SOQPSK method:

Create the comm.SOQPSKModulator 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

soqpskmod = comm.SOQPSKModulator

soqpskmod = comm.SOQPSKModulator(Name=Value)

Description

soqpskmod = comm.SOQPSKModulator creates a modulator System object to modulate input signals using the SOQPSK method.

example

soqpskmod = comm.SOQPSKModulator(Name=Value) sets properties using one or more name-value arguments. For example, comm.SOQPSKModulator(FrequencyPulse='A') specifies type 'A' frequency pulse shaping.

example

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.

`FrequencyPulse` — Type of frequency pulse shaping
`'TG'` (default) | `'A'` | `'B'`

Type of frequency pulse shaping used by the modulator to smooth the phase transitions of the modulated signal, specified as 'TG', 'A', or 'B'. For more information, see Pulse Shape Filtering.

`InitialConditions` — Precoder initial input
[0 0] (default) | scalar | row vector

Precoder initial input, specified as a binary-valued scalar or a two-element row vector. When provided as a scalar, the same value applies to both elements.

This property defines the first data symbol used by the modulator before the first call of the object, in reverse chronological order.

`InitialPhaseOffset` — Initial phase offset
`0` (default) | scalar

Initial phase offset in radians, specified as a scalar. This parameter value is the initial phase offset of the modulated waveform.

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

Symbol sampling rate, specified as a positive even integer. This property specifies the output symbol upsampling factor for each input sample.

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

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

Usage

Syntax

Y = soqpskmod(X)

Description

Y = soqpskmod(X) applies the SOQPSK method to the input signal and returns the modulated SOQPSK baseband signal.

example

Input Arguments

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`X` — Binary-valued data
column vector

Binary-valued data, specified as a column vector with an even number of elements.

This object accepts variable-size inputs. After the object is locked, you can change the frame size (number of rows) of the signal during simulation. For more information, see Variable-Size Signals in Code.

Data Types: single | double | int8

Output Arguments

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`Y` — SOQPSK-modulated baseband output
column vector

SOQPSK-modulated baseband output, returned as a column vector with (length (X)/2)*N_SPS. The number of samples per symbol, N_SPS, is specified by the SamplesPerSymbol property. Use the OutputDataType property to specify the output data type.

Data Types: double | single
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
`reset`	Reset internal states of System object

Examples

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Generate IRIG-106 Based SOQPSK-TG Signal

Open Live Script

Generate an SOQPSK-TG signal that conforms to the IRIG-106 standard for telemetry.

Create an SOQPSK modulator object configured to apply type TG frequency pulse shaping.

txmod = comm.SOQPSKModulator;

Differentially encode random binary data according to IRIG-106, Chapter 2.

data = randi([0 1],200,1);
iData = data(1:2:end);
qData = data(2:2:end);
qBit = 0;
for n = 1:length(iData)
    iData(n) = xor(data((n-1)*2+1),~qBit);
    qData(n) = xor(data((n-1)*2+2),iData(n));
    qBit = qData(n);
end
preInp = zeros(2*length(iData),1);
preInp(1:2:end) = iData;
preInp(2:2:end) = qData;

Modulate the differentially encoded data.

txOut = txmod(preInp);
eyediagram(txOut,16)

Figure Eye Diagram contains 2 axes objects. Axes object 1 with title Eye Diagram for In-Phase Signal, xlabel Time, ylabel Amplitude contains an object of type line. This object represents In-phase. Axes object 2 with title Eye Diagram for Quadrature Signal, xlabel Time, ylabel Amplitude contains an object of type line. This object represents Quadrature.

Apply SOQPSK Modulation

Open Live Script

Create an SOQPSK System object configured for SOQPSK-TG pulse shaping. Modulate a frame of random data using the SOQPSK-TG modulator object.

soqpskMod = comm.SOQPSKModulator(FrequencyPulse="TG");
data = randi([0 1],1e4,1);
sigtg = soqpskMod(data);

Release and reconfigure the object to SOQPSK-A-modulate the frame of data. Modulate the frame of random data using the SOQPSK-A modulator object.

release(soqpskMod)
soqpskMod.FrequencyPulse='A';
siga = soqpskMod(data);

Release and reconfigure the object to SOQPSK-B-modulate the frame of data. Modulate the frame of random data using the SOQPSK-B modulator object.

release(soqpskMod)
soqpskMod.FrequencyPulse='B';
sigb = soqpskMod(data);

Plot the spectral response for each modulated signal.

scope = spectrumAnalyzer( ...
    SampleRate=8e6, ...
    ChannelNames={'TG','A','B'});
scope([sigtg,siga,sigb])

Plot an eye diagram for the SOQPSK-TG-modulated signal.

eyediagram(sigtg,16)

Plot an eye diagram for the SOQPSK-A-modulated signal.

eyediagram(siga,16)

Plot an eye diagram for the SOQPSK-B-modulated signal.

eyediagram(sigb,16)

Compare OQPSK and SOQPSK Modulation

Open Live Script

Show similarity between OQPSK and SOQPSK modulation schemes.

Generate OQPSK-modulated and SOQPSK-modulated data by using the comm.OQPSKModulator and comm.OQPSKDemodulator System objects. Plot different signal characteristics to showcase the similarities between the two modulation schemes.

Create SOQPSK and OQPSK modulator objects. The bit-to-symbol mapping in SOQPSK follows this pattern:

$α = {(- 1)}^{i + 1} \frac{a_{i - 1} (a_{i} - a_{i - 2})}{2}$

To match the SOQPSK bit-to-symbol pattern, use custom symbol mapping in the OQPSK modulator object.

sps = 8;
soqpskmod = comm.SOQPSKModulator(SamplesPerSymbol=sps);
oqpskmod = comm.OQPSKModulator(BitInput=true, ...
    SamplesPerSymbol=sps,SymbolMapping=[3 1 0 2]);

Generate random transmission data and modulate the data using the SOQPSK and OQPSK schemes.

data = randi([0 1],80,1);
y1 = oqpskmod(data);
y2 = soqpskmod(data);

Show the modulated OQPSK and SOQPSK IQ-signal samples by using an XY plot.

figure(1)
subplot(2,1,1)
plot(real(y1));
hold on
if soqpskmod.FrequencyPulse == "B"
    filtdelay = sps*8/2;   
else
    filtdelay = sps*4/2; 
end
plot(real(y2(filtdelay+1:end)))
title('In-Phase Signal Data')
legend('OQPSK','SOQPSK')
xlabel('Samples')
ylabel('Amplitude')
subplot(2,1,2)
plot(imag(y1));
hold on
plot(imag(y2(filtdelay+1:end)))
title('Quadrature Signal Data')
legend('oqpsk','soqpsk')
xlabel('Samples')
ylabel('Amplitude')

Figure contains 2 axes objects. Axes object 1 with title In-Phase Signal Data, xlabel Samples, ylabel Amplitude contains 2 objects of type line. These objects represent OQPSK, SOQPSK. Axes object 2 with title Quadrature Signal Data, xlabel Samples, ylabel Amplitude contains 2 objects of type line. These objects represent oqpsk, soqpsk.

Show the OQPSK signal traces in an eye diagram.

eyediagram(y1,2*oqpskmod.SamplesPerSymbol)

Show the SOQPSK signal traces in an eye diagram.

eyediagram(y2,2*soqpskmod.SamplesPerSymbol)

Algorithms

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This implementation of the SOQPSK method conforms to the specification in IRIG Standard 106-17, Chapter 2 [1], and includes support for SOQPSK-TG, SOQPSK-A, and SOQPSK-B frequency pulse-shapes.

SOQPSK Method

The SOQPSK method is a family of constant-envelope CPM waveforms. This block diagram from Section 2.3.3.2 of IRIG Standard 106-17 shows the input signal flow through a precoder, a pulse shaping filter, and a modulator:

Precoding performed on binary input data generates ternary symbols {–1,0,1}. The Q branch is offset from the I branch by T_b, where T_b is the bit duration in seconds. For each new bit the precoder processes, the modulator outputs a new ternary symbol.

The ternary symbol mapping follows these rules:

$\begin{array}{l} a_{k} = {\begin{matrix} - 1, k^{t h} b i t = 0 \\ + 1, k^{t h} b i t = 1 \end{matrix} \\ α_{k} = (^{- 1) k + 1} \frac{a_{k - 1} (a_{k} - a_{k - 2})}{2} \end{array}$

The SOQPSK precoder uses this mapping for input data:

SOQPSK Precoding Table for IRIG-106 Compatibility
Map α_K from I_K					Map α_K+1 from Q_K+1
I_k	Q_k–1	I_k–2	ΔΦ	α_k	Q_k+1	I_k	Q_k–1	ΔΦ	α_k+1
–1	+1 or –1	–1	0	0	–1	+1 or –1	–1	0	0
+1	+1 or –1	+1	0	0	+1	+1 or –1	+1	0	0
–1	–1	+1	–π/2	–1	–1	–1	+1	+π/2	+1
–1	+1	+1	+π/2	+1	–1	+1	+1	–π/2	–1
+1	–1	–1	+π/2	+1	+1	–1	–1	–π/2	–1
+1	+1	–1	–π/2	–1	+1	+1	–1	+π/2	+1
Included from Table 2-5 in IRIG Standard 106-17

Since I and Q do not vary at the same instant, the ternary symbols generated are constrained so that in a given bit interval, a precoded symbol can be mapped from the set {0,–1} or {0,+1}. Specifically, +1 cannot be followed by –1 and vice versa.

For SOQPSK, the modulation index is ½. The output of the modulator is a baseband representation of the modulated signal:

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

Pulse Shape Filtering

The SOQPSK method uses pulse shaping to smooth the phase transitions of the modulated signal. The function q(t) is the phase response obtained from the frequency pulse, g(t), through this relation:

$q (t) = \int_{- \infty}^{t} g (t) d t$

The specified frequency pulse shape corresponds to a spectrally raised cosine windowed by a modified temporal raised-cosine function expression for g(t).

$\begin{array}{l} g (t) = n (t) w (t) \\ w h e r e \\ n (t) = [\frac{A \cos π θ_{1} (t)}{1 - 4 θ_{_{1}}^{2} (t)}] [\frac{\sin θ_{2} (t)}{θ_{2} (t)}] \\ θ_{1} (t) = \frac{ρ B t}{T_{S}} \\ θ_{2} (t) = \frac{π B t}{T_{S}} \\ w (t) = \frac{1}{2} [1 + \cos (\frac{π (| \frac{t}{T_{S}} | - T_{1})}{T_{2}})], \begin{matrix} 1, | \frac{t}{T_{S}} | \\ T_{1} < | \frac{t}{T_{S}} | \leq T_{1} + T_{2} \\ 0, | \frac{t}{T_{S}} | > T_{1} + T_{2} \end{matrix} \end{array}$

The function n(t) is a modified spectral raised cosine filter of amplitude A, rolloff factor ρ, and an additional time scaling factor B.

The function w(t) is a time domain windowing function that limits the duration of g(t).

The SOQPSK-TG, -A, and -B frequency pulse-shapes use these parameters to realize the spectral raised cosine pulse shape filtering variants.

SOQPSK Type	ρ	B	T1	T2	Resulting Pulse Length (Bit Duration)
SOQPSK-TG (IG 106-04)	0.7	1.25	1.5	0.5	8
SOQPSK-A	1	1.35	1.4	0.6	8
SOQPSK-B	0.5	1.45	2.8	1.2	16

For more information on pulse shape filtering, see Section 2.3.3.2 of IRIG Standard 106-17.

References

[1] Inter-Range Instrumentation Group (IRIG) Telemetry Standards, IRIG Standard 106-17, Chapter 2, July 2017.

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

comm.SOQPSKModulator

Description

Creation

Syntax

Description

Properties

`FrequencyPulse` — Type of frequency pulse shaping
`'TG'` (default) | `'A'` | `'B'`

`InitialConditions` — Precoder initial input
[0 0] (default) | scalar | row vector

`InitialPhaseOffset` — Initial phase offset
`0` (default) | scalar

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

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

Usage

Syntax

Description

Input Arguments

`X` — Binary-valued data
column vector

Output Arguments

`Y` — SOQPSK-modulated baseband output
column vector

Object Functions

Common to All System Objects

Examples

Generate IRIG-106 Based SOQPSK-TG Signal

Apply SOQPSK Modulation

Compare OQPSK and SOQPSK Modulation

Algorithms

SOQPSK Method

Pulse Shape Filtering

References

Extended Capabilities

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

Version History

See Also

Objects

Topics

comm.SOQPSKModulator

Description

Creation

Syntax

Description

Properties

FrequencyPulse — Type of frequency pulse shaping 'TG' (default) | 'A' | 'B'

InitialConditions — Precoder initial input [0 0] (default) | scalar | row vector

InitialPhaseOffset — Initial phase offset 0 (default) | scalar

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

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

Usage

Syntax

Description

Input Arguments

X — Binary-valued data column vector

Output Arguments

Y — SOQPSK-modulated baseband output column vector

Object Functions

Common to All System Objects

Examples

Generate IRIG-106 Based SOQPSK-TG Signal

Apply SOQPSK Modulation

Compare OQPSK and SOQPSK Modulation

Algorithms

SOQPSK Method

Pulse Shape Filtering

References

Extended Capabilities

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

Version History

See Also

Objects

Topics

`FrequencyPulse` — Type of frequency pulse shaping
`'TG'` (default) | `'A'` | `'B'`

`InitialConditions` — Precoder initial input
[0 0] (default) | scalar | row vector

`InitialPhaseOffset` — Initial phase offset
`0` (default) | scalar

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

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

`X` — Binary-valued data
column vector

`Y` — SOQPSK-modulated baseband output
column vector

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