Barker Code Generator

Generate bipolar Barker Code

• Library:

• Communications Toolbox

  Communications Toolbox / Comm Sources / Sequence Generators

• 

Description

The Barker Code Generator block generates a bipolar Barker code. The short length and low correlation sidelobes make Barker codes useful for frame synchronization in digital communications systems. For more information, see Barker Codes.

Ports

Output

output — Barker code frame

column vector

Barker code frame, returned as a column vector. If the frame length exceeds the Barker code length, the block fills the frame by repeating the Barker code.

Dependencies

Set the data type of the output with the Output data type parameter.

Parameters

Code length — Length of generated code

7 (default) | 1 | 2 | 3 | 4 | 5 | 11 | 13

Length of the generated code, specified as 1, 2, 3, 4, 5, 7, 11, or 13. For more information, see Barker Codes.

Example: 2 outputs the Barker code [–1;1].

Data Types: double

Sample time — Output sample time

1 (default) | -1 | positive scalar

Positive scalars specify the time in seconds between each sample of the output signal. If you set the Sample time to -1, the output signal inherits the sample time from downstream. For information on the relationship between the Sample time and Samples per frame parameters, see Sample Timing.

Samples per frame — Samples per output frame

1 (default) | positive integer

Samples per output frame, specified as a positive integer. If Samples per frame is M, the block outputs a frame containing M samples comprised of length N Barker code sequences. N is the length of the generated code, which is set by the Code length parameter. When M is not an integer multiple of N, consecutive frames maintain continuity of the Barker code across frame boundaries.

For information on the relationship between Sample time and Samples per frame, see Sample Timing.

Data Types: double

Output data type — Output data type

double (default) | int8

Output data type, specified as double or int8.

Data Types: char | string

Simulate using — Type of simulation to run

Code generation (default) | Interpreted execution

Type of simulation to run, specified as Code generation or Interpreted execution.

• Code generation –– Simulate the model by using generated C code. The first time you run a simulation, Simulink^® generates C code for the block. The C code is reused for subsequent simulations unless the model changes. This option requires additional startup time, but the speed of the subsequent simulations is faster than Interpreted execution.

• Interpreted execution –– Simulate the model by using the MATLAB^® interpreter. This option requires less startup time than the Code generation method, but the speed of subsequent simulations is slower. In this mode, you can debug the source code of the block.

Model Examples

Generate Barker Code With Various Code Lengths

The cm_ex_various_barker_code_length model shows the output from Barker Code Generator blocks configured for 15 samples per frame at a sample time of 1, and code lengths set to 3, 4, 7, and 13. The plot shows that the code sequence repeats, as needed, to fill a 15 sample frame.

Detect Barker Code Preamble in Frames

Construct two frames consisting of a 7-bit Barker code preamble and a 14-bit payload field. Detect the preamble locations by using the Preamble Detector block.

Frame Synchronization Using Barker Code Preamble

Use a length 13 Barker code frame preamble for frame synchronization of data bits.

Block Characteristics

Data Types	double | integer
Multidimensional Signals	no
Variable-Size Signals	no

More About

Barker Codes

Barker codes have a maximum autocorrelation sequence, which has off-peak autocorrelations no larger than 1.

A correlation sidelobe is the correlation of a codeword with a time-shifted version of itself. The correlation sidelobe, C_k, for a k-symbol shift of an N-bit code sequence, {X_j}, is

$$C_k={\displaystyle \sum _{j=1}^{N-k}{X}_j{X}_{j+k}}$$

For j=1, 2, 3,..., N, X_j is an individual code symbol that is equal to +1 or –1. The adjacent symbols are assumed to be 0.

The output code is in a bipolar format with 0 and 1 mapped to 1 and –1. The maximum known Barker code length is 13. The short length and low correlation sidelobes make Barker codes useful for frame synchronization in digital communications systems. The Barker code generator outputs the Barker codes listed in this table.

Barker Code Length	Barker Code	Sidelobe Level
1	[–1]	0 dB
2	[–1; 1]	–6 dB
3	[–1; –1; 1]	–9.5 dB
4	[–1; –1; 1; –1]	–12 dB
5	[–1; –1; –1; 1; –1]	–14 dB
7	[–1; –1; –1; 1; 1; –1; 1]	–16.9 dB
11	[–1; –1; –1; 1; 1; 1; –1; 1; 1; –1; 1]	–20.8 dB
13	[–1; –1; –1; –1; –1; 1; 1; –1; –1; 1; –1; 1; –1]	–22.3 dB

Sample Timing

The time between output updates is equal to the product of the Samples per frame and Sample time parameter values. For example, if Sample time and Samples per frame each equal 1, the block outputs a sample every second. If you increase Samples per frame to 10, then the block outputs a 10-by-1 vector every 10 seconds. This ensures that the equivalent output rate is not dependent on the Samples per frame parameter.

Compatibility Considerations

Existing models automatically update this block to current version

Behavior changed in R2020a

Starting in R2020a, Simulink no longer allows you to use the Barker Code Generator block version available before R2015b.

Existing models automatically update to load the Barker Code Generator block version announced in Source blocks output frames of contiguous time samples but do not use the frame attribute in the R2015b Release Notes. For more information on block forwarding, see Maintain Compatibility of Library Blocks Using Forwarding Tables (Simulink).

Extended Capabilities

C/C++ Code Generation

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

Does not support integer only code generation.