comm.WalshCode

Generate bipolar Walsh code

Description

The comm.WalshCode System object™ generates a bipolar Walsh code from an orthogonal set of codes.

To generate a Walsh code:

1. Create the comm.WalshCode 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

walshCode = comm.WalshCode

walshCode = comm.WalshCode(Name=Value)

Description

walshCode = comm.WalshCode creates a Walsh code generator System object. This object generates a Walsh code from a set of orthogonal codes.

walshCode = comm.WalshCode(Name=Value) sets properties using one or more name-value arguments. For example, Length=11 specifies a Walsh code of length 11.

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.

Length — Length of generated code

64 (default) | power-of-two integer

Length of generated code, specified as a power-of-two integer.

Data Types: double

Index — Index of desired code

60 (default) | integer in the range [0, N-1]

Index of desired code, from the available set of codes, specified as an integer in the range [0, N-1]. N is the value of the Length property.

The number of zero crossings in the generated code equals the value of the specified index.

Data Types: double

SamplesPerFrame — Samples per output frame

1 (default) | positive integer

Samples per output frame, specified as a positive integer. If you set this property to M, the object outputs a frame containing M samples using the Walsh code specified by the Index property. The object repeats the Walsh code sequence, as needed, to reach M samples. For more information, see Algorithms section.

Data Types: double

OutputDataType — Output data type

double (default) | int8

Output data type, specified as double or int8.

Usage

Syntax

y = walshCode

Description

y = walshCode outputs a bipolar Walsh code frame as a column vector. If the frame length exceeds the Walsh code length, the object fills the frame by repeating the Walsh code. For more information, see the Algorithms section.

Output Arguments

y — Walsh code

column vector

Walsh code, returned as a column vector.

The code is in a bipolar format with 0 and 1 mapped to 1 and -1. Set the data type of the output with 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

Generate Walsh Code Sequence

Generate a Walsh code of length 128. Specify the sequence with 16 samples per frame.

walsh = comm.WalshCode;
walsh.Length = 128;
walsh.SamplesPerFrame = 16;
disp(walsh)

  comm.WalshCode with properties:

             Length: 128
              Index: 60
    SamplesPerFrame: 16
     OutputDataType: 'double'

Display the bipolar Walsh code.

seq = walsh()

seq = 16×1

     1
     1
    -1
    -1
     1
     1
    -1
    -1
     1
     1
      ⋮

Walsh Code Sequence at Desired Index

Generate a Walsh code of length 256. Set the index of the desired code to 64 and the code sequence to 4 samples per frame.

walsh = comm.WalshCode;
walsh.Length = 256;
walsh.Index = 64;
walsh.SamplesPerFrame = 4;
disp(walsh)

  comm.WalshCode with properties:

             Length: 256
              Index: 64
    SamplesPerFrame: 4
     OutputDataType: 'double'

Display the bipolar Walsh code.

seq = walsh()

seq = 4×1

     1
     1
    -1
    -1

Algorithms

Walsh codes are defined as a set of N codes, denoted W_j, for j = 0, 1, ... , N - 1, which have the following properties:

• W_j takes on the values +1 and -1.

• W_j[0] = 1 for all j.

• W_j has exactly j zero crossings, for j = 0, 1, ... , N - 1.

• $$W_j{W}_k^T=\{\begin{array}{cc}0& j\ne k\\ N& j=k\end{array}$$

• Each code Wj is either even or odd with respect to its midpoint.

Walsh codes are defined using a Hadamard matrix of order N, where N is a nonnegative power of 2 that you specify in the Length property. The comm.WalshCode System object outputs a row of the Hadamard matrix. Use the Index property to choose the row of the Hadamard matrix. If you set the Index property equal to an integer j, the output code has exactly j zero crossings, for j = 0, 1, ... , N - 1.

Note, however, that the indexing in Walsh code is different from the indexing in Hadamard code.

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