satellite transponder nonlinearity effect on QAM

Hi i am trying to implement 16QAM modulation with effect of transponder
nonlinearity i got transponder power input and output values and i have to
pass my modulated signal through this nonlinear channel but am not getting
how to perform this function . so if anyone here has done such sort of
work i.e. implemented a satellite nonlinear channel with any modulation
scheme please let me know how to do it. thanking you in advance.

>Hi i am trying to implement 16QAM modulation with effect of transponder
>nonlinearity i got transponder power input and output values and i have
to
>pass my modulated signal through this nonlinear channel but am not
getting
>how to perform this function . so if anyone here has done such sort of
>work i.e. implemented a satellite nonlinear channel with any modulation
>scheme please let me know how to do it. thanking you in advance.
>
>
>sorry to describe before that all of this i am implementing using matlab
communication tool box... so contribution from anyone will be
appreciated... thanking you once again
>

juniar wrote:
> >Hi i am trying to implement 16QAM modulation with effect of transponder
> >nonlinearity i got transponder power input and output values and i have
> to
> >pass my modulated signal through this nonlinear channel but am not
> getting
> >how to perform this function . so if anyone here has done such sort of
> >work i.e. implemented a satellite nonlinear channel with any modulation
> >scheme please let me know how to do it. thanking you in advance.
> >
> >
> >sorry to describe before that all of this i am implementing using matlab
> communication tool box... so contribution from anyone will be
> appreciated... thanking you once again
> >

Can you model the amplifier AM-AM and AM-PM curves using polynomials
(polyfit)? Then you could pass a polar version of your signal through
the polynomials.

John

>
>juniar wrote:
>> >Hi i am trying to implement 16QAM modulation with effect of
transponder
>> >nonlinearity i got transponder power input and output values and i
have
>> to
>> >pass my modulated signal through this nonlinear channel but am not
>> getting
>> >how to perform this function . so if anyone here has done such sort
of
>> >work i.e. implemented a satellite nonlinear channel with any
modulation
>> >scheme please let me know how to do it. thanking you in advance.
>> >
>> >
>> >sorry to describe before that all of this i am implementing using
matlab
>> communication tool box... so contribution from anyone will be
>> appreciated... thanking you once again
>> >
thanks john but i have done that using polyfit function i have generated
the graphs but the actual thing that i mentioned is that i could not get
the values of the alpha and beta coefficients for the AM/AM and AM/PM so
that i could sort out this problem.... or can u explain how u mean to pass
polar version of signal through the polinomial the other thing is i tried
to get the magnitude of the signal using abs function but still cant find
the way to pass it through polynomial to get its effect.... can u please
refer me to some reference where such an implementation is described or if
u can give me some lines of code to do that.... that would be really very
helpfull.... thanking you mate.....
>
>Can you model the amplifier AM-AM and AM-PM curves using polynomials
>(polyfit)? Then you could pass a polar version of your signal through
>the polynomials.
>
>John
>
>

>

>> >
>
>Can you model the amplifier AM-AM and AM-PM curves using polynomials
>(polyfit)? Then you could pass a polar version of your signal through
>the polynomials.
>
>John


i have modeled this using these lines of codes....

power_In=[0.0022 0.0025 0.0028 0.0032 0.0035 0.0039 0.0045 0.0050 0.0056
0.0063 0.0071 0.0079 0.0089 0.0099 0.011 0.013 0.014 0.016 0.018 0.019
0.022 0.025 0.028 0.032 0.035 0.039 0.045 0.050 0.056 0.063 0.071 0.079
0.089 0.099 0.112 0.126 0.141 0.158 0.178 0.199 0.224 0.251];

power_Out=[3.12 3.51 3.94 4.42 4.95 5.56 6.24 6.99 7.85 8.81 9.89 11.09
12.45 13.96 15.67 17.58 19.70 22.08 24.69 27.61 30.83 34.39 38.33 42.56
47.15 52.06 57.08 62.30 67.38 72.28 76.65 80.45 83.56 85.80 87.39 87.90
86.99 84.92 82.22 78.98 74.98 55.72];

co=polyfit(power_In,power_Out,5)
new=polyval(co,power_In)
plot(power_In,power_Out,'*',power_In,new,':')


in above lines of codes power_In and power_Out are satellite transponder
powers respectively... and i have generated a polynomial using polyfit
with upto 5 polynomials.... but if i have my signal in a variable called
signal with complex number.... how i can pass this signal through this
polynomial.... and allso i got my signal's power by using abs function
wich gives the magnitude. please help me finding the way to pass the
signal through this ploynomial ... or infact this transponder model....
thanks.... 

values for phase change in degrees are also here...

phase_Ch=[0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
0.00 0.00 0.05 0.36 0.78 1.30 1.95 2.70 3.60 4.65 5.90 7.35 9.05 10.99
13.22 15.81 18.69 21.83 25.17 28.66 32.15 35.52 38.97 42.37 45.76 48.96
51.78 54.26 56.51]

hello John....
I am waiting for your reply mate... I am still not getting how to pass
polar version of my signal through the polynomial...it would be great help
from you if u give me some example or refer to any link where it has been
explained that how to do this....
please do help me....i really need to find out solution to this problem.
thanking you once again in advance,
bye

"juniar" <umarmahmud@hotmail.com> wrote in message 
news:9dWdnfu-M4aFunHZnZ2dnUVZ_oCdnZ2d@giganews.com...
> hello John....
> I am waiting for your reply mate... I am still not getting how to pass
> polar version of my signal through the polynomial...it would be great help
> from you if u give me some example or refer to any link where it has been
> explained that how to do this....
> please do help me....i really need to find out solution to this problem.
> thanking you once again in advance,
> bye

Hi Juniar - it will help if you polyfit to a set of points describing an odd 
function. You seem to have input amplitudes spaced in 1 dB steps, correctly 
translated to linear but you need to invert the order and make them negative 
then stick them on the front of the data points you already have - now when 
you do polyfit you should get 0th , 2nd and 5th harmonic very near zero 
indicating that you can ignore them, the only things you are interested in 
are 1st , 3rd and 5th harmonics.
Now when you do your plot to find out how good the fit is - using only 1st 
3rd and 5th order coefficients from polyfit it should be a bit closer.   Now 
you have the output amplitudes - all you should need to do is figure out how 
to determine what the additional phase shift is for each input power level, 
add the appropriate phase shift to the input phase  to determine what the 
phase of your output sample is.

Best of Luck - Mike

>Hi i am trying to implement 16QAM modulation with effect of transponder
>nonlinearity i got transponder power input and output values and i have
to
>pass my modulated signal through this nonlinear channel but am not
getting
>how to perform this function . so if anyone here has done such sort of
>work i.e. implemented a satellite nonlinear channel with any modulation
>scheme please let me know how to do it. thanking you in advance.
>
>
>
>

If you have the inputs and output of the nonlinear system, then all you
need to do is solve a system identification problem using a Volterra
series.  I have done this before using both LMS and block-least squares to
solve for the Volterra coefficients.  

Warning:  Volterra models can become prohibitively large if the
non-linearity has a long memory.