Communications Blockset™

CPFSK Modulator Baseband

Modulate using continuous phase frequency shift keying method

Library

CPM, in Digital Baseband sublibrary of Modulation

Description

The CPFSK Modulator Baseband block modulates using the continuous phase frequency shift keying method. The output is a baseband representation of the modulated signal. The M-ary number parameter, M, is the size of the input alphabet. M must have the form 2^K for some positive integer K.

The Modulation index parameter times π radians is the phase shift due to the latest symbol when that symbol is the integer 1. The Phase offset parameter is the initial phase of the output waveform, measured in radians.

For the exact definitions of the rectangular pulse shape that this block uses, see the work by Anderson, Aulin, and Sundberg among the references listed below.

Inputs and Symbol Sets

If the Input type parameter is set to Integer, then the block accepts odd integers between -(M-1) and M-1.

If the Input type parameter is set to Bit, then the block accepts groupings of K bits. Each grouping is called a binary word. The input vector length must be an integer multiple of K.

In binary input mode, the block maps each binary word to an integer between 0 and M-1, using a mapping that depends on whether the Symbol set ordering parameter is set to Binary or Gray. The block then maps the integer k to the intermediate value 2k-(M-1) and proceeds as in the integer input mode. For more information, see Binary-Valued and Integer-Valued Signals in Communications Blockset™ User's Guide.

The input can be either a scalar or a frame-based column vector. If Input type is Bit, then the input can also be a vector of length K.

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

M-ary number: The size of the alphabet.
Input type: Indicates whether the input consists of integers or groups of bits.
Symbol set ordering: Determines how the block maps each group of input bits to a corresponding integer. This field is active only when Input type is set to Bit.
Modulation index: The number of half-revolutions of phase shift due to the latest symbol when that symbol is the integer 1.
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 binary word in the input.
Output datatype: The output data type can be single or double.

Pair Block

CPFSK Demodulator Baseband

References

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