Help me plot the eye-diagram for this sinc wave

[Serial_Expert]

Re: eyediagram question

Hi,
I am trying to plot the eyediagram for the following sinc wave :


a=0.35; % excess bandwidth
T=(-2:0.05:2); %scaled time T here is t/Tb where Tb=1/(2B) ,
Signal1=sinc(T).*cos((pi*a).*T)./(1-((4*a^2).*(T.^2)));
eyediagram(Signal1,length(T)/2);


but I don't get the proper eye pattern,


I highly appreciate any help in this,,


Regards,,,

Added after 2 minutes:

I forgot to mention that I am using the Matlab function eyediagram() ,
Thanks,,

 

[amraldo]

Re: eyediagram question

I used simulink before for getting eye-diagrams when i made a model for bluetooth transciever.
I think, I am not sure of that, eye-diagrams are for periodic outputs with same amplitude. For example, pulses & sinewaves. where the eye width is half the period.
In ur case with sinc T the perid is 2*pi. so in plotting the area from 0 to pi & from -pi to 0 will differ from all other peiods. u should take care of that.
Any way try to wirte it like this:

eyediagram(Signal1,pi) but after increasng ur T array for example from -10*pi to 10*pi.
Regards,
Amr.

 

[Serial_Expert]

eyediagram question

Hi Amr,
The eyediagram function in Matlab accept only integer value for the second argument .
I believe that I need to multiply the Signal1 with the a random bit sequence , and then use the sampling rate & the data bit rate in the function .
What I am looking for is the relation between what I already mentioned in the above.
Thank you again for your support,
Regards,,

 

[Serial_Expert]

eyediagram question

After several tests & investigation I can now draw the correct
eyediagram with the following code:
ss=[-1 1];
ind = randint(500,1,2);
ind = ind+1;
seq = ss(ind);
a=0.35;
T=(-6:0.2:6);
nsamp=(length(T)-1)/(max(T)*2);
Signal1=sinc(T).*cos((pi*a).*T)./(1-((2*a.*T).^2));
ytx = rcosflt(seq,1,nsamp,'fir/filter',Signal1);
eyediagram(ytx,2*nsamp,2);
But I still see strange (almost 0 amplitude average) curve line in the
middle of the eye , Any one know why this line is appreaing?
Regards....