Rectangular QAM Demodulator Passband (Communications Blockset)

Demodulate QAM-modulated data

Library

AM, in Digital Passband sublibrary of Modulation

Description

The Rectangular QAM Demodulator Passband block demodulates a signal that was modulated using quadrature amplitude modulation with a constellation on a rectangular lattice. The signal constellation has M points, where M is the M-ary number parameter. M must have the form 2^K for some positive integer K.

This block converts the input to an equivalent baseband representation and then uses the baseband equivalent block, M-PAM 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
Normalization method
Minimum distance
Average power
Peak power

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
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 points in the signal constellation. It must have the form 2^K for some positive integer K.
Output type: Indicates 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.
Normalization method: Determines how the block scales the signal constellation. Choices are Min. distance between symbols, Average Power, and Peak Power.
Minimum distance: The distance between two nearest constellation points. This field appears only when Normalization method is set to Min. distance between symbols.
Average power (watts): The average power of the symbols in the constellation. This field appears only when Normalization method is set to Average Power.
Peak power (watts): The maximum power among the symbols in the constellation. This field appears only when Normalization method is set to Peak Power.
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

Rectangular QAM Modulator Passband

References

[1] Smith, Joel G, "Odd-Bit Quadrature Amplitude-Shift Keying," IEEE Transactions on Communications, vol. COM-23, March 1975, pp. 385-389.

Rectangular QAM Demodulator Baseband Rectangular QAM Modulator Baseband