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Simulators >> System Simulators >> simulating a BPSK system in simulink
https://designers-guide.org/forum/YaBB.pl?num=1245687123

Message started by .matteo on Jun 22^nd, 2009, 9:12am

Title: simulating a BPSK system in simulink
Post by .matteo on Jun 22^nd, 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 ;)

-Matteo

Title: Re: simulating a BPSK system in simulink
Post by pancho_hideboo on Jun 22^nd, 2009, 9:15am

.matteo wrote on Jun 22^nd, 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

Title: Re: simulating a BPSK system in simulink
Post by .matteo on Jun 22^nd, 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?

Title: Re: simulating a BPSK system in simulink
Post by .matteo on Jun 22^nd, 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?

Title: Re: simulating a BPSK system in simulink
Post by pancho_hideboo on Jun 22^nd, 2009, 9:45am

.matteo wrote on Jun 22^nd, 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 22^nd, 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".

Title: Re: simulating a BPSK system in simulink
Post by .matteo on Jun 22^nd, 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?

Title: Re: simulating a BPSK system in simulink
Post by pancho_hideboo on Jun 22^nd, 2009, 9:59am

Read wireless communication theory textbook and documents of Simulink.

.matteo wrote on Jun 22^nd, 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 ?

Title: Re: simulating a BPSK system in simulink
Post by .matteo on Jun 22^nd, 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

Title: Re: simulating a BPSK system in simulink
Post by pancho_hideboo on Jun 23^rd, 2009, 3:33am

.matteo wrote on Jun 22^nd, 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

Title: Re: simulating a BPSK system in simulink
Post by Ken Kundert on Jun 23^rd, 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

Title: Re: simulating a BPSK system in simulink
Post by .matteo on Jun 24^th, 2009, 5:35pm

Thanks everybody, now my system works great and I learned a lot of interesting stuff ;)