Comment generer une gapped clock avec Simulink

Une gapped clock est utilisé dans les implementations telecom pour pouvoir demapper une payload avec un bitrate M depuis un signal qui a un bitrate N. Avec M<N.

Pratiquement on utilise un clock lié à la frequence du bitrate N, auquel, de temps au autres on enlève un pulse.

Un exemple dans l'image en pj.

Dans mon cas, il y a un premier skip après 11 cycles et ensuite un skip après 12 cycles. Ensuite la sequence se repète ... 11 cycles - skip - 12 cycles - skip ... etc etc

J'aurais besoin de generer ce type de signal pour ensuite l'étudier en analyse spectrale.

Pourriez-vous me donner des indication de comment generer sous Simulink ?

Merci d'avance

Answer 1

[Suraj Kumar]

Hi Andrea,

Based on my understanding, you want to generate signals similar to a gapped clock i.e. to skip the pulse after a few cycles. To generate the required signals, you can follow these steps:

1. Add the following blocks onto the Simulink canvas:

• Pulse Generator Block: Generates a periodic pulse and acts as an input to MATLAB Function block.
• MATLAB Function Block: Implements the logic to skip specific cycles.
• Scope Block: Visualizes the output signal from the MATLAB Function Block.

2. Configure the Pulse Generator Block with the following parameters:

• Amplitude = 1 , sets the height of the pulse signal
• Period = 1 , defines the duration of one complete cycle
• Pulse Width = 50% , sets the duty cycle of the pulse.

3. Implement the following logic in the MATLAB Function Block to skip cycles as required :

function y = skip_cycles(u)
% Persistent variable to keep track of the cycle count
persistent cycle_count;
if isempty(cycle_count)
    cycle_count = 0;
end
cycle_count = cycle_count + 1;
if cycle_count > 23
    cycle_count = 1;
end
% Skip cycle logic
if cycle_count == 12 || cycle_count == 23
    y = 0;
else
    y = u;
end
end

4. Run the model and observe the results from the Scope Block.

You can refer the output given below:

For more information on the ‘Pulse Generator’,’ MATLAB Function’ and ‘Scope’ blocks in Simulink, kindly refer to the following documentations:

• Pulse Generator block: https://www.mathworks.com/help/simulink/slref/pulsegenerator.html
• MATLAB Function Block: https://www.mathworks.com/help/simulink/slref/matlabfunction.html
• Scope Block: https://www.mathworks.com/help/simulink/slref/scope.html

Hope this helps!