Communications Blockset™

GMSK Modulator Baseband - Modulate using Gaussian minimum shift keying method

Library

CPM, in Digital Baseband sublibrary of Modulation

Description

The GMSK Modulator Baseband block modulates using the Gaussian minimum shift keying method. The output is a baseband representation of the modulated signal.

The BT product parameter represents bandwidth multiplied by time. This parameter is a nonnegative scalar. It is used to reduce the bandwidth at the expense of increased intersymbol interference. The Pulse length parameter measures the length of the Gaussian pulse shape, in symbol intervals. For an explanation of the pulse shape, see the work by Anderson, Aulin, and Sundberg among the references listed below. The frequency pulse shape is defined by the following equations.

The Symbol prehistory parameter is a scalar or vector that specifies the data symbols used before the start of the simulation, in reverse chronological order. If it is a vector, then its length must be one less than the Pulse length parameter.

In this block, a symbol of 1 causes a phase shift of π/2 radians. The Phase offset parameter is the initial phase of the output waveform, measured in radians.

Input Attributes

The input can be either a scalar or a frame-based column vector. If the Input type parameter is set to Integer, then the block accepts values of 1 and -1. If the Input type parameter is set to Bit, then the block accepts values of 0 and 1.

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 Communications Blockset™ User's Guide.

Dialog Box

Input type: Indicates whether the input consists of bipolar or binary values.
BT product: The product of bandwidth and time.
Pulse length (symbol intervals): The length of the frequency pulse shape.
Symbol prehistory: The data symbols used before the start of the simulation, in reverse chronological order.
Phase offset (rad): The initial phase of the output waveform.
Samples per symbol: The number of output samples that the block produces for each integer or bit in the input.
Output data type: The output type of the block can be specified as a single or double. By default, the block sets this to double.

Pair Block

GMSK Demodulator Baseband

References

[1] Anderson, John B., Tor Aulin, and Carl-Erik Sundberg. Digital Phase Modulation. New York: Plenum Press, 1986.