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Simulators >> System Simulators >> Using Simulink to model a RF transceiver
https://designers-guide.org/forum/YaBB.pl?num=1233929450

Message started by AnalogAroma on Feb 6^th, 2009, 6:10am

Title: Using Simulink to model a RF transceiver
Post by AnalogAroma on Feb 6^th, 2009, 6:10am

Hi Everybody,

I have been experiencing some problems to model a RF transceiver in Simulink. My baseband signal has a BW of 4MHz. But when I upconvert this signal at 1GHz , the shifted baseband signal spectrum seems very strange !!

Any simulink expert available in this forum ?

Title: Re: Using Simulink to model a RF transceiver
Post by pancho_hideboo on Feb 6^th, 2009, 7:17pm

AnalogAroma wrote on Feb 6^th, 2009, 6:10am:

I have been experiencing some problems to model a RF transceiver in Simulink.
My baseband signal has a BW of 4MHz. But when I upconvert this signal at 1GHz , the shifted baseband signal spectrum seems very strange !!

Show me your block diagram of Simulink and resulting Spectrum.

How to model upconverter in Simulink ?
Just simply multiplier ? Or using Mixer in RF block set ?

Which of model in the followings do you use ?
(1)BB-Signal, I(t)+j*Q(t) --->　Real RF Signal, (I(t)+j*Q(t))*exp(j*omega0*t)
(2)BB-Signal, I(t)+j*Q(t) --->　Equivalent Lowpass Representation of RF Signal, {I(t)+j*Q(t), omega0}

What solver do you use in Simulink ?
Continuous or Discrete ?
What time step control do you use ?

If you use (1), time step is enough small ?

Title: Re: Using Simulink to model a RF transceiver
Post by AnalogAroma on Feb 10^th, 2009, 1:45pm

Show me your block diagram of Simulink and resulting Spectrum.
------------
AA : Please see the attached file. A pdf file containing the spectrums will be added later.
-------------------------------
How to model upconverter in Simulink ?
Just simply multiplier ? Or using Mixer in RF block set ?
------------------------------------------
AA: I have used a multiplier.

----------------------------------------------
Which of model in the followings do you use ?
(1)BB-Signal, I(t)+j*Q(t) --->　Real RF Signal, (I(t)+j*Q(t))*exp(j*omega0*t)
(2)BB-Signal, I(t)+j*Q(t) --->　Equivalent Lowpass Representation of RF Signal, {I(t)+j*Q(t), omega0}
--------------------------------------
AA: Method 1 , real RF signal.
------------------------------------
What solver do you use in Simulink ?
Continuous or Discrete ?
-------------------------------------
AA : Discrete
-------------------------------------
What time step control do you use ?
If you use (1), time step is enough small ?
------------------------------------
AA : Variable time step. Max time step is auto. I have also used
10 ps , but no improvement !

Title: Re: Using Simulink to model a RF transceiver
Post by AnalogAroma on Feb 10^th, 2009, 1:48pm

pancho_hideboo wrote on Feb 6^th, 2009, 7:17pm:

AnalogAroma wrote on Feb 6^th, 2009, 6:10am:

The signal spectrums are shown in the attached pdf file.

Title: Re: Using Simulink to model a RF transceiver
Post by pancho_hideboo on Feb 12^th, 2009, 7:16am

Maybe due to rate mismatch between BB and LO signals.
Insert upsampler for BB or set upsample ratio in raised cosine filter.
If you upload your block dirgram, I can modify.

Title: Re: Using Simulink to model a RF transceiver
Post by AnalogAroma on Feb 12^th, 2009, 7:26am

Thanks a lot for your kind feedback. The zipped Simulink model is attached herewith.

Title: Re: Using Simulink to model a RF transceiver
Post by pancho_hideboo on Feb 13^th, 2009, 8:58am

Frame time lengths before mixer are different in your setting while you use frame-based sampling mode.

Title: Re: Using Simulink to model a RF transceiver
Post by pancho_hideboo on Feb 13^th, 2009, 8:59am

This is my setting.

Title: Re: Using Simulink to model a RF transceiver
Post by pancho_hideboo on Feb 13^th, 2009, 9:04am

These are results of spectrum.

Why do you set LO frequency as 1GHz ?
In simulink model, you don't have to set LO frequency as real frequency.
So you should use Equivalent Lowpass Representation of RF Signal or low frequency as LO.
BB-Signal, I(t)+j*Q(t) --->　Equivalent Lowpass Representation of RF Signal, {I(t)+j*Q(t), omega0}

Title: Re: Using Simulink to model a RF transceiver
Post by AnalogAroma on Feb 14^th, 2009, 3:33am

Wow ! Your simulation results look fantastic. I want to use your settings to do simulate the transeiver in my office computer.

But from the last Thursday evening, I have been sick and will not go to the office for several days. After my recovery, I will post my replies again.

Title: Re: Using Simulink to model a RF transceiver
Post by AnalogAroma on Mar 11^th, 2009, 9:46am

Hi PH,

I am back from the hospital. After following your setting , I have got properly upconverted spectrum. Howerver, I can not zoom the spectrum.
I have played with several options, but the spectrum resolution is not as good as yours. Which setting have you used in the fft plot ? May I have a look and run you Simulink file on my side ?

Title: Re: Using Simulink to model a RF transceiver
Post by pancho_hideboo on Mar 13^th, 2009, 9:10am

AnalogAroma wrote on Mar 11^th, 2009, 9:46am:

Hi PH,

Who is he ? Don't use unfamiliar abbreviations. I don't like very local abbreviations such as "U R right", "Do U", "thank u", "BR", "ViVA, ADE, CDF of Cadence", etc.

See attached model of Simulink.

Title: Re: Using Simulink to model a RF transceiver
Post by AnalogAroma on Mar 13^th, 2009, 4:34pm

Hi Pancho_hideboo,

After applying your Spectrum scope settings , I have got really cool
spectrums !! Now , modelling in Simulink seems to be enjoyable.
Thanks a lot to dispel my initial frustration with Simulink !