FSK using baseband modulation

Question

al-comm 2011-6-17

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/9771-fsk-using-baseband-modulation

回答： Derek Eccles 2019-4-9

Hello,

I want to create a FSK modulator using the "*M-FSK Modulator Baseband*" block, the input is Bernoulli Binary Generator (0, 1) , but i cant get the good output ( 2 different frequencies ) on the scope in real time !!??

Block diagram : http://imageshack.us/photo/my-images/854/blocks.jpg/

Good Output signal : http://imageshack.us/photo/my-images/820/outputu.jpg/

Bad Output signal : http://imageshack.us/photo/my-images/825/signalsk.jpg/

P.S : the output shown is bad because the frequency is the same whatever the input is 0 or 1. !!!

Thanks a lot,

Bye

2 个评论
显示无隐藏无

Rick Rosson 2011-6-17

Can you please post a screen shot showing the mask parameters (dialog box settings) of the 2-FSK modulator block? Thanks!

al-comm 2011-6-19

Hello Rick,

Thanks for your comment and sorry for late, I’ve not received any notification for your comment,

Anyway, here are the mask parameters:

http://imageshack.us/photo/my-images/225/setupx.jpg/

P.S: Even if I choose Binary or Gray the result is the same, and the sampling by symbol parameter does not give a good signal too …

This part is bugging my project,

Waiting for answer please,

Thanks again,

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Rick Rosson 2011-6-20

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/9771-fsk-using-baseband-modulation#answer_13536

The output of the Simulink model is correct. The reason that it is not the same as the "Good Output signal" is that the Simulink signal is the complex baseband equivalent of the desired FSK signal, whereas the "Good Output signal" is the real-valued passband signal. Although these two signals are not the same, they are related.

In fact, you can generate the real-valued passband signal in the Simulink model by adding a handful of blocks that represent the passband modulation. To do so, multiply the output of the baseband modulator by a complex exponential at the desired passband frequency, and then view the real- and imaginary- parts on the scope.

HTH.

3 个评论
显示 1更早的评论隐藏 1更早的评论

Rick Rosson 2011-6-20

What are your specific questions?

Please let me know.

Thanks!

al-comm 2011-6-20

Hello,

I see the difference between Baseband and Passeband, I’ve multiplied the baseband output modulator by complex exponential, but I still can’t see the good output...

My schematic:

http://imageshack.us/photo/my-images/18/expt.jpg/

All parameters are kept the same, and I’ve tested the complex exponential with different frequencies from 10 Hz to 10 KHz…

Thanks a lot.

请先登录，再进行评论。

Answer 2

Rick Rosson 2011-6-21

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/9771-fsk-using-baseband-modulation#answer_13637

在 MATLAB Online 中打开

You are getting closer to the right answer, but still not quite there yet. In your schematic, you are feeding the output of a real-valued sine wave to the input of the complex exponential function. So the output of the complex exponential block is:

exp(j*sin(2*pi*Fc*t))

where Fc represents the carrier frequency (in hertz). This modulation signal is not quite correct.

The correct output of the complex exponential should be:

exp(j*2*pi*Fc*t)

That means the input to the complex exponential function should be the simulation clock t feeding a gain block with a value of 2*pi*Fc.

Please give that a try.

Alternatively, I believe that you can generate a complex exponential output from the Sine Wave block. Please check the dialog box.

HTH.

Rick