Rectangular QAM Modulator Passband (Communications Blockset)

Modulate using M-ary quadrature amplitude modulation

Library

AM, in Digital Passband sublibrary of Modulation

Description

The Rectangular QAM Modulator Passband block modulates using M-ary quadrature amplitude modulation with a constellation on a rectangular lattice. The output is a passband representation of the modulated signal. 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 uses the baseband equivalent block, Rectangular QAM Modulator Baseband, for internal computations and converts the resulting baseband signal to a passband representation. The following parameters in this block are the same as those of the baseband equivalent block:

M-ary number
Input type
Constellation ordering
Normalization method
Minimum distance
Average power
Peak power

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:

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

Furthermore, Carrier frequency is typically much larger than the highest frequency of the unmodulated signal.

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.
Input type: Indicates whether the input consists of integers or groups of bits.
Constellation 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.
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 of the symbols in the constellation. This field appears only when Normalization method is set to Peak Power.
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: The sample time of the output signal.

Pair Block

Rectangular QAM Demodulator Passband

References

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

Rectangular QAM Modulator Baseband Rician Fading Channel