Communications Blockset    
CPM Modulator Passband

Modulate using continuous phase modulation

Library

CPM, in Digital Passband sublibrary of Modulation

Description

The CPM Modulator Passband block modulates using continuous phase modulation. The output is a passband representation of the modulated signal. The M-ary number parameter, M, is the size of the input alphabet. M must have the form 2K for some positive integer K.

This block uses the baseband equivalent block, CPM Modulator Baseband, for internal computations and converts the resulting baseband signal to a passband representation, using FIR interpolation and then upconversion. The following parameters in this block are the same as those of the baseband equivalent block:

The input must be sample-based. If the Input type parameter is Bit, then the input must be a vector of length log2(M). If the Input type parameter is Integer, then the input must be a scalar.

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:

where Fmax is defined as follows:

Fmax = [Frequency separation * (M-ary number - 1) / 2] + 1 / Symbol period

The Carrier frequency parameter is typically much larger than the highest frequency of the baseband signal.

The CPM Modulator Passband block creates a delay in signals that it processes. This delay is caused by FIR filters in the block, whose tap length depends on signal and simulation parameters.

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.
Frequency pulse shape
The type of pulse shaping that the block uses to smooth the phase transitions of the modulated signal.
Main lobe pulse duration (symbol intervals)
Number of symbol intervals of the largest lobe of the spectral raised cosine pulse. This field is active only when Frequency pulse shape is set to Spectral Raised Cosine.
Rolloff
The rolloff factor of the raised cosine filter. This field appears only when Frequency pulse shape is set to Spectral Raised Cosine.
BT product
The product of bandwidth and time. This field appears only when Frequency pulse shape is set to Gaussian.
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.
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(s)
The sample time of the output signal.

Pair Block

CPM Demodulator Passband

See Also

CPM Modulator Baseband

References

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


  CPM Modulator Baseband CRC-N Generator