Communications Blockset™

QPSK Modulator Baseband - Modulate using quaternary phase shift keying method

Library

PM in Digital Baseband sublibrary of Modulation

Description

The QPSK Modulator Baseband block modulates using the quaternary phase shift keying method. The output is a baseband representation of the modulated signal.

Inputs and Constellation Types

If the Input type parameter is set to Integer, then valid input values are 0, 1, 2, and 3. If Constellation ordering is set to Binary, for input m the output symbol is

exp(jθ + jπm/2)

where θ is the Phase offset parameter (see the following figure for Gray constellation ordering). In this case, the input can be either a scalar or a frame-based column vector.

For integer inputs, the block can accept the data types int8, uint8, int16, uint16, int32, uint32, single, and double. For bit inputs, the block can accept int8, uint8, int16, uint16, int32, uint32, boolean, single, and double.

If the Input type parameter is set to Bit, then the input contains pairs of binary values. The input can be either a vector of length 2 or a frame-based column vector whose length is an even integer. If the Phase offset parameter is set to pi/4, then the block uses one of the signal constellations in the following figure, depending on whether the Constellation ordering parameter is set to Binary or Gray.

Dialog Box

Phase offset (rad)

The phase of the zeroth point of the signal constellation.

Constellation ordering

Determines how the block maps each pair of input bits or input integers to constellation symbols.

Input type

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

Output data type

The output data type can be set to 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.

Set output fraction length to

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

Choose Best precision to have the output scaling automatically set such that the output signal has the best possible precision.
Choose User-defined to specify the output scaling in the Output fraction length parameter.

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

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 Simulink Fixed Point. This parameter is only visible when you select User-defined for the Output data type parameter.

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 is only visible 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.

Pair Block