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DQPSK Modulator Baseband - Modulate using differential quaternary phase shift keying method

Library

PM, in Digital Baseband sublibrary of Modulation

Description

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

The input must be a discrete-time signal. 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.

Inputs and Constellation Types

If the Input type parameter is set to Integer, then valid input values are 0, 1, 2, and 3. In this case, the input can be either a scalar or a frame-based column vector. If the first input is m, then the modulated symbol is

exp(jθ + jπm/2)

where θ is the Phase rotation parameter. If a successive input is m, then the modulated symbol is the previous modulated symbol multiplied by exp(jθ + jπm/2).

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 two or a frame-based column vector whose length is an even integer. The figure below shows the complex numbers by which the block multiples the previous symbol to compute the current symbol, depending on whether the Constellation ordering parameter is set to Binary or Gray. The figure assumes that the Phase rotation parameter is set to pi/4; in other cases, the two schematics would be rotated accordingly.

The figure below shows the signal constellation for the DQPSK modulation method when the Phase rotation parameter is π/4. The arrows indicate the four possible transitions from each symbol to the next symbol. The Binary and Gray options determine which transition is associated with each pair of input values.

More generally, if the Phase rotation parameter has the form π/k for some integer k, then the signal constellation has 2k points.

Dialog Box

Input type: Indicates whether the input consists of integers or pairs of bits.
Constellation ordering: Determines how the block maps each pair of input bits to a corresponding integer. This field is active only when Input type is set to Bit.
Phase rotation (rad): The phase difference between the previous and current modulated symbols when the input is zero.
Output Data type: The output data type can be either single or double. By default, the block sets this to double.

Pair Block

DQPSK Demodulator Baseband