General QAM Demodulator Passband (Communications Blockset)

Demodulate QAM-modulated data

Library

AM, in Digital Passband sublibrary of Modulation

Description

The General QAM Demodulator Passband block demodulates a signal that was modulated using the pulse amplitude phase shift keying method. The input is a passband representation of the modulated signal.

The input must be a sample-based scalar. Furthermore, it must be a discrete-time complex signal.

The Signal constellation parameter defines the constellation by listing its points in a vector of complex numbers.

Parameters Specific to Passband Simulation

Passband simulation uses a carrier signal. The Carrier frequency and Carrier initial phase parameters specify the frequency and initial phase, respectively, of the carrier signal. The Input sample time parameter specifies the sample time of the input signal, while the Symbol period parameter equals the sample time of the output signal.

This block uses a baseband representation of the modulated signal as an intermediate signal during internal computations. The Baseband samples per symbol parameter indicates how many baseband samples correspond to each integer or binary word in the output.

The timing-related parameters must satisfy these relationships:

Symbol period > (Carrier frequency)^-1
Input sample time < [2*Carrier frequency + 2/(Symbol period)]^-1

Also, this block incurs an extra output period of delay compared to its baseband equivalent block.

Note A model containing this block must use a variable-step solver. To configure a model so that it uses a variable-step solver, select Simulation parameters from the model window's Simulation menu and then set the Type parameter on the Solver panel to Variable-step.

Dialog Box

Signal constellation: A real or complex vector that lists the constellation points.
Symbol period (s): The symbol period, which equals the sample time of the output.
Baseband samples per symbol: The number of baseband samples that represent each modulated symbol, after the block converts the passband input to a baseband intermediary signal.
Carrier frequency (Hz): The frequency of the carrier.
Carrier initial phase (rad): The initial phase of the carrier in radians.
Input sample time: The sample time of the input signal.

Pair Block

General QAM Modulator Passband

See Also

General QAM Demodulator Baseband

General QAM Demodulator Baseband General QAM Modulator Baseband