M-DPSK Demodulator Passband (Communications Blockset)

Demodulate DPSK-modulated data

Library

PM, in Digital Passband sublibrary of Modulation

Description

The M-DPSK Demodulator Passband block demodulates a signal that was modulated using the M-ary differential phase shift keying method. The input is a passband representation of the modulated signal. The input and output for this block are discrete-time signals. The input must be a sample-based scalar signal.

The M-ary number parameter, M, is the number of possible output symbols that can immediately follow a given output symbol. The block compares the current symbol to the previous symbol. The block's first output is the initial condition of zero because there is no previous symbol.

This block converts the input to an equivalent baseband representation and then uses the baseband equivalent block, M-DPSK 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
Constellation ordering

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

Also, this block incurs an extra output period of delay compared to its baseband equivalent block.

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

M-ary number: The number of possible modulated symbols that can immediately follow a given symbol.
Output type: Determines whether the output consists of integers or groups of bits.
Constellation 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.
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: The sample time of the input signal.

Pair Block

M-DPSK Modulator Passband

See Also

M-DPSK Demodulator Baseband

References

[1] Pawula, R. F. "On M-ary DPSK Transmission Over Terrestrial and Satellite Channels." IEEE Transactions on Communications, vol. COM-32, July 1984. 752-761.

M-DPSK Demodulator Baseband M-DPSK Modulator Baseband