Contents

OQPSK Modulator Baseband

Modulate using offset quadrature phase shift keying method

Library

PM, in Digital Baseband sublibrary of Modulation

Description

The OQPSK Modulator Baseband block modulates using the offset quadrature phase shift keying method. The block outputs a baseband representation of the modulated signal.

    Note:   The OQPSK modulator block upsamples by a factor of 2.

When you set the Input type parameter to Integer, valid input values are 0, 1, 2, and 3. In this case, the block accepts a scalar or a column vector input signal.

When you set the Input type parameter to Bit, a binary-valued vector is a valid input value. In this case, the block accepts a column vector input signal with a length that is an even integer.

For information about the data types each block port supports, see Supported Data Types.

The constellation the block uses to map bit pairs to symbols is shown in the following figure. If you set the Phase offset parameter to a nonzero value, then the constellation rotates by that value.

Single-Rate Processing

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 input to the block can be multiple symbols.

  • 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 half the period of each integer or bit pair in the input.

To open this modelopen this model, type doc_moqpskmod_fb at the MATLAB® command line.

Multirate Processing

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 Input type to Integer, the input must be a scalar value.

  • When you set Input type to Bit, the input width must equal 2.

The output sample time equals one-half the symbol period. The first output symbol is an initial condition of zero that is unrelated to the input values.

To open this modelopen this model, type doc_moqpskmod_sb at the MATLAB command line.

Delays

The modulator-demodulator pair incurs a delay, as described in Delays in Digital Modulation.

Dialog Box

Phase offset (rad)

The amount by which the block shifts the phase of the zeroth point of the signal constellation from π/4.

Input type

Indicates whether the input consists of integers or pairs of bits.

Rate options

Select the rate processing option for the block.

  • Enforce single-rate processing — When you select this option, 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. The output width equals two times the number of symbols for integer inputs.

  • Allow multirate processing — When you select this option, the input and output signals have different port sample times. The output sample time equals one-half the symbol period.

      Note:   The option Inherit from input (this choice will be removed - see release notes) will be removed in a future release. See Frame-Based Processing in the Communications System Toolbox™ Release Notes for more information.

Output data type

Select the output data type as double, single, Fixed-point, User-defined, or Inherit via back propagation.

Setting this parameter to Fixed-point or User-defined enables fields in which you can further specify details. Setting this parameter to Inherit via back propagation, sets the output data type and scaling to match the following block.

Output word length

Specify the word length, in bits, of the fixed-point output data type. This parameter is only visible when you select Fixed-point for the Output data type parameter.

User-defined data type

Specify any signed built-in or signed fixed-point data type. You can specify fixed-point data types using the sfix, sint, sfrac, and fixdt functions from Fixed-Point Designer™. This parameter is only visible when you select User-defined for the Output data type parameter.

Set output fraction length to

Specify the scaling of the fixed-point output by either of the following methods:

  • When you select Best precision the block sets the output scaling so the output signal has the best possible precision.

  • When you select User-defined you specify the output scaling using the Output fraction length parameter.

This parameter applies when you select Fixed-point for the Output data type parameter or you select User-defined and the specified output data type is a fixed-point data type.

Output fraction length

For fixed-point output data types, specify the number of fractional bits, or bits to the right of the binary point. This parameter applies when you select Fixed-point or User-defined for the Output data type parameter and User-defined for the Set output fraction length to parameter.

Supported Data Types

PortSupported Data Types

Input

  • Double-precision floating point

  • Single-precision floating point

  • Boolean when Input type is Bit

  • 8-, 16-, and 32-bit signed integers

  • 8-, 16-, and 32-bit unsigned integers

  • ufix(1) when Input type is Bit

  • ufix(2) when Input type is Integer

Output

  • Double-precision floating point

  • Single-precision floating point

  • Signed fixed point

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