comm.PSKTCMModulator

Encode binary data using convolutional encoder and map result to M-PSK constellation

Description

The comm.PSKTCMModulator System object™ implements trellis-coded modulation (TCM) by encoding the binary input signal using a convolutional code and by mapping the result to an M-ary phase shift keying (PSK) signal constellation. For more information about TCM, see the Algorithms section.

To encode binary data using a convolutional code and map the result to an M-PSK constellation:

1. Create the comm.PSKTCMModulator object and set its properties.

2. Call the object with arguments, as if it were a function.

To learn more about how System objects work, see What Are System Objects?

Creation

Syntax

psktcmMod = comm.PSKTCMModulator

psktcmMod = comm.PSKTCMModulator(trellis)

psktcmMod = comm.PSKTCMModulator(___,Name=Value)

Description

psktcmMod = comm.PSKTCMModulator creates a PSK TCM modulator System object, psktcmMod. This object employs a convolutional encoder to encode a binary input signal and maps the result to an M-PSK constellation.

psktcmMod = comm.PSKTCMModulator(trellis) additionally sets the TrellisStructure property to trellis.

psktcmMod = comm.PSKTCMModulator(___,Name=Value) creates a PSK TCM modulator System object using any of the previous syntaxes and sets properties using one or more name-value arguments. For example, comm.PSKTCMDemodulator(ModulationOrder=4) sets the number of points in the signal constellation to 4.

Properties

Unless otherwise indicated, properties are nontunable, which means you cannot change their values after calling the object. Objects lock when you call them, and the release function unlocks them.

If a property is tunable, you can change its value at any time.

For more information on changing property values, see System Design in MATLAB Using System Objects.

TrellisStructure — Trellis structure of convolutional code

poly2trellis([1 3], [1 0 0; 0 5 2]) (default) | structure

Trellis structure of the convolutional code, specified as a MATLAB^® structure that contains the trellis description of the convolutional code. Use the istrellis function to check whether a trellis structure is valid.

The trellis structure contains these fields.

numInputSymbols — Number of symbols input to encoder

2^K

Number of symbols input to the encoder, specified as an integer equal to 2^K, where K is the number of input bit streams.

numOutputSymbols — Number of symbols output from encoder

2^N

Number of symbols output from the encoder, specified as an integer equal to 2^N, where N is the number of output bit streams.

numStates — Number of states in encoder

power of 2

Number of states in the encoder, specified as a power of 2.

nextStates — Next states

matrix of integers

Next states for all combinations of current states and current inputs, specified as a matrix of integers. The matrix size must be numStates by 2^K.

outputs — Outputs

matrix of octal numbers

Outputs for all combinations of current states and current inputs, specified as a matrix of octal numbers. The matrix size must be numStates by 2^K.

Data Types: struct

TerminationMethod — Termination method of encoded frame

"Continuous" (default) | "Truncated" | "Terminated"

Termination method of the encoded frame, specified as one of these options.

• "Continuous" — The object retains the encoder states at the end of each input vector for use with the next input vector.

• "Truncated" — The object treats each input vector independently. The encoder is reset to the all-zeros state at the start of each input vector.

• "Terminated" — The object treats each input vector independently. However, for each input vector, the object uses extra bits to set the encoder to the all-zeros state at the end of the vector. For a rate K/N code, the convolutional encoder outputs the vector with a length given by $$\frac{N\times (L+S)}{K}$$, where S = constraintLength–1 (or, in the case of multiple constraint lengths, S = sum(constraintLength(i)–1)). L indicates the length of the input.

ResetInputPort — Modulator reset input

false or 0 (default) | true or 1

Modulator reset input, specified as a logical 0 (false) or 1 (true). Set this property to true to call the object with an additional input. For nonzero reset input values, the internal states of the encoder reset to initial conditions.

Dependencies

To enable this property, set the TerminationMethod property to "Continuous".

ModulationOrder — Number of points in signal constellation

8 (default) | 4 | 16

Number of points in the signal constellation, specified as 4, 8, or 16. The value of the ModulationOrder property must equal the number of possible output symbols from the convolutional encoder of the PSK TCM modulator. Therefore, the value for the ModulationOrder property must equal 2^N for a rate K/N convolutional code.

Data Types: single | double

OutputDataType — Data type of output

"double" (default) | "single"

Data type of the output, specified as "double" or "single".

Usage

Syntax

Y = psktcmMod(X)

Y = psktcmMod(X,R)

Description

Y = psktcmMod(X) applies PSK TCM to the input data, X, and returns the trellis-coded M-PSK modulated data, Y.

Y = psktcmMod(X,R) resets the encoder of the PSK TCM modulator object to the all-zeros state when you input a reset signal, R, that is nonzero. This syntax applies when you set the value of the ResetInputPort property to true.

Input Arguments

X — Input binary data

column vector

Input binary data, specified as a column vector. X must be of data type numeric, logical, or unsigned fixed point of word length 1 (fi object). For a rate K/N code, the length of the input vector, X, must be K×Q (which equals L), for some positive integer Q.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | logical | fi

R — Reset signal

false or 0 (default) | true or 1 | numeric scalar

Reset signal, specified as a logical 0 (false), 1 (true), or numeric scalar.

Dependencies

To use this argument, set the ResetInputPort property to true.

Data Types: double | logical

Output Arguments

Y — Output data

column vector

Output data, returned as a column vector. The length of Y is Q. The data type of the output data depends on the OutputDataType property.

Object Functions

To use an object function, specify the System object as the first input argument. For example, to release system resources of a System object named obj, use this syntax:

release(obj)

Common to All System Objects

step	Run System object algorithm
release	Release resources and allow changes to System object property values and input characteristics
reset	Reset internal states of System object

Examples

Modulate Data Using 8-PSK TCM Modulation

Modulate random data using 8-PSK TCM modulation and display the constellation diagram.

Create binary data.

data = randi([0 1],1000,1);

Define a trellis structure with four input symbols and eight output symbols.

trellis =  poly2trellis([5 4],[23 35 0; 0 5 13]);

Create an 8-PSK TCM modulator object using the trellis structure variable, t.

psktcmMod = comm.PSKTCMModulator(trellis,ModulationOrder=8);

Modulate and plot the data.

modData = psktcmMod(data);
scatterplot(modData);

Algorithms

The trellis-coded M-PSK modulation uses a set partitioning technique to map the result of the convolutional encoder to a PSK signal constellation. The trellis-coded modulation technique partitions the constellation into subsets called cosets to maximize the minimum distance between pairs of points in each coset.

This figure shows the labeled set-partitioned signal constellation that the object uses when the M-ary number is 8.

References

[1] Biglieri, E., D. Divsalar, P.J. McLane, and M.K. Simon. Introduction to Trellis-Coded Modulation with Applications. New York: Macmillan, 1991.

[2] Proakis, John G. Digital Communications. 4th ed. New York: McGraw Hill, 2001.

[3] Ungerboeck, G. “Channel Coding with Multilevel/Phase Signals.” IEEE^® Transactions on Information Theory IT28 (Jan. 1982): 55–67.

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

See System Objects in MATLAB Code Generation (MATLAB Coder).

Version History

Introduced in R2012a