M-FSK Demodulator Passband (Communications Blockset)

Modulate using the M-ary frequency shift keying method

Library

FM, in Digital Passband sublibrary of Modulation

Description

The M-FSK Demodulator Passband block demodulates a signal that was modulated using the M-ary frequency shift keying method. The input is a passband representation of the modulated signal. The M-ary number parameter, M, is the number of frequencies in the modulated signal.

This block converts the input to an equivalent baseband representation using downconversion and then FIR decimation. The block then uses the baseband equivalent block, M-FSK Demodulator Baseband, for internal computations. The following parameters in this block are the same as those of the baseband equivalent block:

M-ary number
Output type
Signal set ordering
Frequency separation

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 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
Symbol period must be an integer multiple of the product of Output sample time and Baseband samples per symbol.
Output sample time < [2*Carrier frequency + 2*F_max)]^-1

where F_max is defined as follows:

F_max = [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 M-FSK Demodulator 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.

The Symbol period parameter must be an integer multiple of the product of Output sample time times Baseband samples per symbol.

Dialog Box

M-ary number: The number of frequencies in the modulated signal.
Output type: Determines whether the output consists of integers or groups of bits. If this parameter is set to Bit, then the M-ary number parameter must be 2^K for some positive integer K.
Symbol set ordering: Determines how the block maps each integer to a group of output bits. This field is active only when Output type is set to Bit.
Frequency separation (Hz): The distance between successive frequencies in the modulated signal.
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(s): The sample time of the input signal.

Pair Block

M-FSK Modulator Passband

M-FSK Demodulator Baseband M-FSK Modulator Baseband