Communications Blockset

General QAM Modulator Passband

Modulate using the pulse amplitude modulation phase shift keying method

Library

AM, in Digital Passband sublibrary of Modulation

Description

The General QAM Modulator Passband block modulates using the pulse amplitude modulation phase shift keying method. The output is a passband representation of the modulated signal.

The Signal constellation parameter defines the constellation by listing its points in a length-M vector of complex numbers. The input signal values must be integers between 0 and M-1. The block maps an input integer m to the (m+1)st value in the Signal constellation vector, and then converts these mapped values to a passband output signal.

The input must be a sample-based scalar signal.

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 Symbol period parameter must equal the sample time of the input signal, while the Output sample time parameter determines the sample time of the output signal.

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

The timing-related parameters must satisfy these relationships:

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

Furthermore, Carrier frequency is typically much larger than the highest frequency of the unmodulated signal.

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 must equal the sample time of the input.

Baseband samples per symbol

The number of baseband samples that correspond to each integer or binary word in the input, before the block converts them to a passband output.

Carrier frequency (Hz)

The frequency of the carrier.

Carrier initial phase (rad)

The initial phase of the carrier in radians.

Output sample time

The sample time of the output signal.

Pair Block

General QAM Demodulator Passband

See Also

General QAM Modulator Baseband

General QAM Modulator Baseband

GMSK Demodulator Baseband