OQPSK Modulator Baseband

Modulate using OQPSK method

Libraries:
Communications Toolbox / Modulation / Digital Baseband Modulation / PSK

Description

The OQPSK Modulator Baseband block modulates the input signal using the offset quadrature phase shift keying (OQPSK) method and applies pulse shape filtering to the waveform. For more information, see Pulse Shaping Filter. The output is a baseband representation of the modulated signal.

For information about delays incurred by modulator-demodulator pair processing, see Modulation Delays.

Examples

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OQPSK Modulator-Demodulator Block Pair Use

This example uses:

Open Model

This example shows the OQPSK Modulator Baseband and OQPSK Demodulator Baseband blocks connected with no channel or impairments distorting the signal between them. They are configured for frame-based processing with bit signal inputs.

Use the Open model button to open the cm_ex_oqpsk_mod_demod_pair model and run the simulation.

The model displays the constellation of the OQPSK-modulated signal and computes the bit error rate of the recovered signal. The delay of the recovered signal, as determined by the Find Delay block, is applied in the Error Rate Calculation block. For perfect data recovery, the bit error rate is zero.

Single-Rate Processing with OQPSK Modulator Block

This example uses:

Open Model

This example shows the OQPSK Modulator Baseband block configured for single-rate processing using integer or bit for the input type.

Use the Open model button to open the slex_oqpskmod_framebased model.

In single-rate processing mode, the input and output signals have the same port sample time. The block implicitly implements the rate change by making a size change at the output when compared to the input. In this mode, the output of the block is an integer multiple of the Samples per symbol parameter.

When you set the Input type parameter to Integer, the input can be a scalar value or column vector, the length of which is the number of input symbols.
When you set the Input type parameter to Bit, the input width must be an integer multiple of two.

The output sample period is the period of each integer or bit pair at the input divided by the Samples per symbol.

Multirate Processing with OQPSK Modulator Block

This example uses:

Open Model

This example shows the OQPSK Modulator Baseband block configured for multirate processing using integer or bit for the input type.

Use the Open model button to open the slex_oqpskmod_samplebased model.

In multirate processing mode, the input and output signals have different port sample times. In this mode, the input to the block must be one symbol.

When you set the Input type parameter to Integer, the input must be a scalar value.
When you set Input type parameter to Bit, the input width must equal two.

The output sample time is the symbol period divided by Samples per symbol. The first output symbol is an initial condition of zero that is unrelated to the input values.

End-to-End Communication System Using IIR Pulses

Open Model

This example shows how to create an end-to-end communication system using OQPSK modulator and demodulator block using Butterworth pulses, custom pulse shape and an AWGN channel. This model also calculates the bit error rate between the transmitter and the receiver.

Use the Open model button to open the cm_ex_oqpskmoddemod_iir model.

In this communication system, to receive the IIR pulses the demodulator is in the Integrate and Dump mode. For this, set the Pulse Shape property to Custom and FilterNumerator to 1.

Ports

Input

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In — Input data
integer column vector | bit column vector

Input data, specified as an integer or bit column vector.

The input signal is processed based on the setting selected for Input type.

Output

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Out — Output baseband waveform
column vector

Output baseband waveform, returned as a column vector of complex data. The Output data type parameter specifies the data type of the output signal.

Parameters

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To edit block parameters interactively, use the Property Inspector. From the Simulink^® Toolstrip, on the Simulation tab, in the Prepare gallery, select Property Inspector.

Modulation

Input type — Input type
`Integer` (default) | `Bit`

Input type, specified as Integer or Bit.

When you set Input type to Integer, the input can be a scalar value or column vector, the length of which is the number of input symbols.
When you set Input type to Bit, the input width must be an integer multiple of two.

The output sample period is the period of each integer or bit pair in the input divided by Samples per symbol.

Symbol mapping — Signal constellation bit mapping
`Gray` (default) | `Binary` | custom 4-element numeric vector of integers with values from 0 to 3

Signal constellation bit mapping, specified as Gray, Binary, or a custom 4-element numeric vector of integers with values from 0 to 3.

Setting	Constellation Mapping for Integers	Constellation Mapping for Bits	Comment
`Gray`			The signal constellation mapping is Gray-encoded.
`Binary`			The signal constellation mapping for the input integer `m` (0 ≤ `m` ≤ 3) is the complex value `e^{(j(PhaseOffset+π/4) + j2πm/4)}`.
Custom 4-element numeric vector of integers with values from 0 to 3			Elements [a b c d] must be composed of the set of values [0, 1, 2, 3] in any order.

Phase offset (rad) — Phase of zeroth point of signal constellation
`0` (default) | scalar

Phase offset from π/4, specified as a scalar in radians. The phase offset is applied to the zeroth point of the signal constellation before delay of quadrature component. After the OQPSK imaginary-component delay, the signal is normalized with unity power.

Example: Setting Phase offset (rad) to pi/4 aligns the zeroth point of the QPSK signal constellation point on the axes, {(1,0), (0,j), (-1,0), (0,-j)}.

View Constellation — Option to plot reference constellation
button

Click View Constellation on the block mask to visualize a signal constellation for the specified block parameters. Before viewing a constellation, apply the parameter settings. For more information, see View Constellation of Modulator Block.

Note

The constellation that displays does not depict the IQ delay introduced by the OQPSK modulator.

Filtering

Pulse shape — Filtering pulse shape
`Half sine` (default) | `Normal raised cosine` | `Root raised cosine` | `Custom`

Select the filtering pulse shape: Half sine, Normal raised cosine, Root raised cosine, or Custom.

Rolloff factor — Raised cosine filter rolloff factor
`0.2` (default) | scalar

Raised cosine filter rolloff factor, specified as a scalar in the range [0, 1].

Dependencies

This property is enabled when Pulse shape is Normal raised cosine or Root raised cosine.

Filter span (in symbols) — Filter length
`10` (default) | scalar

Filter length in symbols, specified as a scalar. An ideal raised cosine filter has an infinite impulse response. However, to realize a practical implementation of this filter, the object truncates the impulse response to Filter span (in symbols) symbols.

Dependencies

This property is enabled when Pulse shape is Normal raised cosine or Root raised cosine.

Filter numerator — Filter numerator
`[0.7071 0.7071]` (default) | row vector

FIR filter numerator, specified as a row vector.

Dependencies

This parameter is enabled when Pulse shape is Custom.

Filter Denominator — Filter denominator
`1` (default) | row vector

FIR filter denominator, specified as a row vector.

Dependencies

This parameter is enabled when Pulse shape is Custom.

Samples per symbol — Number of samples per symbol
`4` (default) | positive even integer

Number of samples per symbol, specified as a positive even integer.

Other Parameters

Rate options — Processing rate option
`Enforce single-rate processing` (default) | `Allow multirate processing`

Enforce single-rate processing — Executes the model, ensuring that the input and output signals have the same port sample time. The block implements the rate change by making a size change at the output when compared to the input. For integer inputs, the output width equals Samples per symbol times the number of symbols.
For an example, see Single-Rate Processing with OQPSK Modulator Block.
Allow multirate processing — Executes the model, allowing the input and output signals to have different port sample times. The output sample time equals the symbol period divided by Samples per symbol.
For an example, see Multirate Processing with OQPSK Modulator Block.

Output data type — Output data type
`double` (default) | `single`

Select the output data type: double or single.

Block Characteristics

Data Types	`Boolean` \| `double` \| `integer` \| `single`
Multidimensional Signals	`no`
Variable-Size Signals	`no`

More About

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Modulation Delays

Digital modulation and demodulation blocks incur delays between their inputs and outputs that result in an offset in the arrival time of the received data. Data that enters a modulation or demodulation block at time T appears in the output at time T+delay. Take system delays into account when comparing transmitted data with received data, such as in overlaid plots or when computing error statistics. As shown here, the OQPSK modulation-demodulation delay varies depending on the pulse shaping filter, input/output data setting, and simulation configuration.

Pulse Shape	Rate Options	Treat Each Discrete Rate as a Separate Task?	Input/Output Data (*)	End-to-End Delay Incurred by an OQPSK Modulator-Demodulator Block Pair (in samples)
`Half sine` or `Custom`	`Enforce single-rate operation`	N/A	`Integer`	1
	`Enforce single-rate operation`	N/A	`Bit`	2
	`Allow multirate processing`	`false` (single tasking)	`Integer`	length(data) + 1 + 1
		`false` (single tasking)	`Bit`	length(data) + 2 + 2
		`true` (multitasking)	`Integer`	length(data) + 1 + 2
		`true` (multitasking)	`Bit`	length(data) + 2 + 4
`Normal raised cosine` or `Root raised cosine`	`Enforce single-rate operation`	N/A	`Integer`	Filter span (in symbols)
	`Enforce single-rate operation`	N/A	`Bit`	2*Filter span (in symbols)
	`Allow multirate processing`	`false` (single tasking)	`Integer`	length(data) + Filter span (in symbols) + 1
		`false` (single tasking)	`Bit`	length(data) + 2*Filter span (in symbols) + 2
		`true` (multitasking)	`Integer`	2length(data) + Filter span (in symbols)* + 2
		`true` (multitasking)	`Bit`	2length(data) + 2Filter span (in symbols) + 4
() The data type parameter is Input type* for modulation and Output type for demodulation.

Pulse Shaping Filter

The OQPSK modulation scheme requires oversampling of two or greater in order to delay (or offset) the quadrature channel by 90 degrees. This oversampling is achieved through interpolation filtering implemented by pulse shaping.

Extended Capabilities

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

Version History

Introduced before R2006a

OQPSK Modulator Baseband

Description

Examples

OQPSK Modulator-Demodulator Block Pair Use

Single-Rate Processing with OQPSK Modulator Block

Multirate Processing with OQPSK Modulator Block

End-to-End Communication System Using IIR Pulses

Ports

Input

In — Input data integer column vector | bit column vector

Output

Out — Output baseband waveform column vector

Parameters

Modulation

Input type — Input type Integer (default) | Bit

Symbol mapping — Signal constellation bit mapping Gray (default) | Binary | custom 4-element numeric vector of integers with values from 0 to 3

Phase offset (rad) — Phase of zeroth point of signal constellation 0 (default) | scalar

View Constellation — Option to plot reference constellation button

Filtering

Pulse shape — Filtering pulse shape Half sine (default) | Normal raised cosine | Root raised cosine | Custom

Rolloff factor — Raised cosine filter rolloff factor 0.2 (default) | scalar

Dependencies

Filter span (in symbols) — Filter length 10 (default) | scalar

Dependencies

Filter numerator — Filter numerator [0.7071 0.7071] (default) | row vector

Dependencies

Filter Denominator — Filter denominator 1 (default) | row vector

Dependencies

Samples per symbol — Number of samples per symbol 4 (default) | positive even integer

Other Parameters

Rate options — Processing rate option Enforce single-rate processing (default) | Allow multirate processing

Output data type — Output data type double (default) | single

Block Characteristics

More About

Modulation Delays

Pulse Shaping Filter

Extended Capabilities

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

Version History

See Also

Blocks

Objects

Topics

In — Input data
integer column vector | bit column vector

Out — Output baseband waveform
column vector

Input type — Input type
`Integer` (default) | `Bit`

Symbol mapping — Signal constellation bit mapping
`Gray` (default) | `Binary` | custom 4-element numeric vector of integers with values from 0 to 3

Phase offset (rad) — Phase of zeroth point of signal constellation
`0` (default) | scalar

View Constellation — Option to plot reference constellation
button

Pulse shape — Filtering pulse shape
`Half sine` (default) | `Normal raised cosine` | `Root raised cosine` | `Custom`

Rolloff factor — Raised cosine filter rolloff factor
`0.2` (default) | scalar

Filter span (in symbols) — Filter length
`10` (default) | scalar

Filter numerator — Filter numerator
`[0.7071 0.7071]` (default) | row vector

Filter Denominator — Filter denominator
`1` (default) | row vector

Samples per symbol — Number of samples per symbol
`4` (default) | positive even integer

Rate options — Processing rate option
`Enforce single-rate processing` (default) | `Allow multirate processing`

Output data type — Output data type
`double` (default) | `single`

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