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simulating a BPSK system in simulink (Read 19059 times)
.matteo
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simulating a BPSK system in simulink
Jun 22nd, 2009, 9:12am
 
Hi everybody,
  Im simulating a BPSK system in simulink. I did everything in the time domain and I'd like to add some phase noise at the output of the channel.

However, when I use the phase noise block in simulink, it only accepts complex signal and my signal is real. How can add phase noise to my real signal?

Any help would be really appreciated Wink

-Matteo
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pancho_hideboo
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Re: simulating a BPSK system in simulink
Reply #1 - Jun 22nd, 2009, 9:15am
 
.matteo wrote on Jun 22nd, 2009, 9:12am:
However, when I use the phase noise block in simulink, it only accepts complex signal and my signal is real.
How can add phase noise to my real signal?
Make models as (2) of the following.
http://www.designers-guide.org/Forum/YaBB.pl?num=1233929450/1#1
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.matteo
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Re: simulating a BPSK system in simulink
Reply #2 - Jun 22nd, 2009, 9:32am
 
pancho_hideboo,
  thanks for the help! I attached you my simple model that has just I. Just to make sure I understood correctly, are you saying that I should design a replica of my I to create a model of Q, sum them together such that I transmit I+j*Q so I get a complex number on the channel?
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.matteo
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Re: simulating a BPSK system in simulink
Reply #3 - Jun 22nd, 2009, 9:42am
 
Yes, you re right, I am studying it right now by myself. I come from the math world and I need to simulate a communication system. BPSK has always Q=0 so if I want to create a complex signal I should switch to QPSK, right?
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pancho_hideboo
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Re: simulating a BPSK system in simulink
Reply #4 - Jun 22nd, 2009, 9:45am
 
.matteo wrote on Jun 22nd, 2009, 9:32am:
I attached you my simple model that has just I. Just to make sure I understood correctly, are you saying that I should design a replica of my I to create a model of Q, sum them together such that I transmit I+j*Q so I get a complex number on the channel?
No.
You don't seem to understand concept of equivalent lowpass model for RF bandpass system.
You have to understand this concept correctly if you use system simulator such as Agilent Ptolemy and Mathworks Simulink.

.matteo wrote on Jun 22nd, 2009, 9:42am:
Yes, you re right, I am studying it right now by myself.
I come from the math world and I need to simulate a communication system.
BPSK has always Q=0 so if I want to create a complex signal I should switch to QPSK, right?
No.
Use "Communications Blockset>Modulation>Digital Baseband Modulation>PM>BPSK Modulator Baseband".

Any modulation can be expressed as "QAM" not "QPSK".
However you don't have to use "QAM".



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« Last Edit: Jun 23rd, 2009, 3:44am by pancho_hideboo »  
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.matteo
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Re: simulating a BPSK system in simulink
Reply #5 - Jun 22nd, 2009, 9:54am
 
Ok, I have to think about it.

The block you suggested to me has a constant magnitude output and the phase changes and it s zero or pi, so it makes sense to me. In my model, I can change the freq of the carrier that modulates my barker code, how can I do the same with the complex signal coming out from the BPSK modulator block?
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pancho_hideboo
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Re: simulating a BPSK system in simulink
Reply #6 - Jun 22nd, 2009, 9:59am
 
Read wireless communication theory textbook and documents of Simulink.

.matteo wrote on Jun 22nd, 2009, 9:54am:
The block you suggested to me has a constant magnitude output and the phase changes and it s zero or pi, so it makes sense to me.
In my model, I can change the freq of the carrier that modulates my barker code,
how can I do the same with the complex signal coming out from the BPSK modulator block?

Output signal is complex envelope.
If you need real signal which include carrier, simply multiply it with complex carrier signal and then extract real part.
This is (1) of http://www.designers-guide.org/Forum/YaBB.pl?num=1233929450/1#1

But real signal is not needed generally. You should study an equivalent lowpass model for RF bandpass system.
You can express AM/AM and AM/PM nonlinearity as well as phase noise of carrier signal in an equivalent lowpass model.
Why do you need real signal ?
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« Last Edit: Jun 23rd, 2009, 3:41am by pancho_hideboo »  
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.matteo
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Re: simulating a BPSK system in simulink
Reply #7 - Jun 22nd, 2009, 11:28am
 
I did it with the BPSK modulator and I added my free space loss and the transport delay but the Phase Noise block doesnt accept continuous time samples. How can I do the same with the discrete samples? Is there a more "elegant" way to do it?

Thanks
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pancho_hideboo
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Re: simulating a BPSK system in simulink
Reply #8 - Jun 23rd, 2009, 3:33am
 
.matteo wrote on Jun 22nd, 2009, 11:28am:
I did it with the BPSK modulator and I added my free space loss and the transport delay
but the Phase Noise block doesnt accept continuous time samples.
How can I do the same with the discrete samples?
Is there a more "elegant" way to do it?
Where did you insert "Phase Noise" ?
Do you understand use model of "Communications Blockset>RF Impairments" ?
"Complex baseband model" means "Equivalent lowpass model".
http://en.wikipedia.org/w/index.php?title=Equivalent_lowpass_signal

You should study an equivalent lowpass model for RF bandpass system.

Attend the following training which is charged.
http://www.mathworks.com/services/training/courses/CM01_1.html

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« Last Edit: Jun 23rd, 2009, 4:49am by pancho_hideboo »  
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Ken Kundert
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Re: simulating a BPSK system in simulink
Reply #9 - Jun 23rd, 2009, 11:27am
 
You might want to read Modelling RF Systems (http://www.designers-guide.org/Modeling/modeling-rf-systems.pdf) to get a better understanding of equivalent lowpass modelling of RF systems.

-Ken
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.matteo
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Re: simulating a BPSK system in simulink
Reply #10 - Jun 24th, 2009, 5:35pm
 
Thanks everybody, now my system works great and I learned a lot of interesting stuff Wink
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