comm.HelicalDeinterleaver

Deinterleave symbols using helical array

Description

The comm.HelicalDeinterleaver System object™ permutes the symbols in the input signal by placing them in a row-by-row array and then selecting groups helically to send to the output port. This System object restores the original ordering of a sequence that was interleaved using the comm.HelicalInterleaver System object. For more information, see Algorithms.

To deinterleave symbols using helical array:

1. Create the comm.HelicalDeinterleaver 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

deintrlvr = comm.HelicalDeinterleaver

deintrlvr = comm.HelicalDeinterleaver(Name=Value)

Description

deintrlvr = comm.HelicalDeinterleaver creates a default helical deinterleaver System object.

deintrlvr = comm.HelicalDeinterleaver(Name=Value) sets properties using one or more name-value arguments. For example, NumColumns=6 sets the number of columns in the helical array to 6.

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.

NumColumns — Number of columns in helical array

6 (default) | positive integer

Number of columns in the helical array, specified as a positive integer.

GroupSize — Size of each group of input symbols

4 (default) | positive integer

Size of each group of input symbols, specified as a positive integer.

StepSize — Helical array step size

1 (default) | positive integer

Helical array step size, specified as a positive integer. Step size indicates the number of rows of separation between consecutive input groups in their respective columns of the helical array.

InitialConditions — Initial conditions of helical array

0 (default) | numeric scalar

Initial conditions of the helical array, specified as a numeric scalar value. This is the initial value stored in the helical array.

Usage

Syntax

deintrlvseq = deintrlvr(intrlvseq)

Description

deintrlvseq = deintrlvr(intrlvseq) deinterleaves the input sequence of symbols using the helical array. The object outputs the deinterleaved sequence of symbols.

Input Arguments

intrlvseq — Interleaved sequence of symbols

column vector

Interleaved sequence of symbols, specified as a column vector. Input sequence is of size NumColumns × GroupSize. This sequence must be one that was interleaved using the comm.HelicalInterleaver System object.

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

Output Arguments

deintrlvseq — Deinterleaved sequence of symbols

column vector

Deinterleaved sequence of symbols, returned as a column vector of the same data type and size as the intrlvseq argument.

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

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

Helical Interleaving and Deinterleaving

Create helical interleaver and deinterleaver System objects.

intrlver = comm.HelicalInterleaver(GroupSize=2,NumColumns=3, ...
            InitialConditions=-1);
deintrlvr = comm.HelicalDeinterleaver(GroupSize=2,NumColumns=3, ...
            InitialConditions=-1);

Generate random data. Interleave and then deinterleave the data.

[dataIn,dataOut] = deal([]);
for k = 1:10
    data = randi(7,6,1);
    intData = intrlver(data);
    deIntData = deintrlvr(intData);
    
    dataIn = cat(1,dataIn,data);
    dataOut = cat(1,dataOut,deIntData);
end

Determine the delay through the interleaver and deinterleaver pair.

intlvDelay = finddelay(dataIn,dataOut)

intlvDelay = 
6

After taking the interleaving delay into account, confirm that the original and deinterleaved data are identical.

isequal(dataIn(1:end-intlvDelay),dataOut(1+intlvDelay:end))

ans = logical
   1

Algorithms

Array Processing of Helical Deinterleaver

The helical deinterleaver permutes the symbols in the input signal by placing them in an array row-by-row and then selecting groups in a helical fashion to send to the output port.

The object uses the array internally for its computations. If you set the NumColumns property of the object to C, then the array has C columns and unlimited rows. If you set the GroupSize property to N, then the object accepts an input of length C × N at each time step and inserts them into the next N rows of the array. The object also places the InitialConditions property into certain positions in the top few rows of the array. This placement helps not only to accommodate the helical pattern but also to preserve the vector indices of symbols that pass through the Helical Interleaver and Helical Deinterleaver objects in turn.

The output consists of consecutive groups of N symbols. Counting from the beginning of the simulation, the object selects the k^th output group in the array from column k mod C. This placement is of type helical because of the reduction modulo C, and because the first symbol in the k^th group is in the row 1+(k-1) × s, where s is the value for the StepSize property.

This object accepts a column vector input signal containing C × N elements.

Delay of Helical Interleaving and Deinterleaving

After processing a message with the helical interleaver and deinterleaver pair, the deinterleaved data lags the original message by $$CN\lceil \frac{s(C-1)}{N}\rceil$$ symbols, where:

• C is the value of NumColumns property.

• N is the value of GroupSize property.

• s is the value of StepSize property.

Before this delay elapses, the deinterleaver output is either the InitialConditions property value in the comm.HelicalInterleaver object or the InitialConditions property value in the comm.HelicalDeinterleaver object.

If you incur an additional delay between the interleaver output and the deinterleaver input, then the restored sequence lags the original sequence by the sum of the additional delay and the amount in the formula above. For proper synchronization, the delay between the interleaver and deinterleaver must be m×C×N for some nonnegative integer m. You can use the dsp.Delay object to adjust delays manually, if necessary.

References

[1] Berlekamp, E. R. and P. Tong. "Improved Interleavers for Algebraic Block Codes." US Patent 4559625, Dec. 17, 1985.

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