DQPSK Modulator Baseband (Communications Blockset)

Modulate using the 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.

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

where is the Phase offset parameter. If a successive input is m, then the modulated symbol is the previous modulated symbol multiplied by exp(j + jm/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 offset 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 offset parameter is /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 offset parameter has the form /k for some integer k, then the signal constellation has 2k points.

Upsampling the Modulated Signal

This block can output an upsampled version of the modulated signal. The Samples per symbol parameter is the upsampling factor. It must be a positive integer. For more information, see Upsampled Signals and Rate Changes in Using the Communications Blockset.

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 offset (rad): The phase difference between the previous and current modulated symbols when the input is zero.
Samples per symbol: The number of output samples that the block produces for each integer or pair of bits in the input.

Pair Block

DQPSK Demodulator Baseband

DQPSK Demodulator Baseband DSB AM Demodulator Baseband