Converting a signal to baseband after resampling

Hello,

After resampling a passband signal, how can I convert it back to the baseband domain? In particular, I have the following code in MATLAB:

v=d.*exp(1i*2*pi*fc.*t);
z=resample(v,p,q);

where d and t are the signal and time vector respectively,and fc is the carrier frequency. In this case z after resampling has a different length than v, and hence I cannot write:

zBP=z.*exp(-1i*2*pi*fc.*t);

How can I handle this then?

Thanks

[Rick Rosson]

What are the values of p and q?

[S. David]

p and q are any two integers.

Answer 1

[Rick Rosson]

   Nz = length(z);
   Nv = length(v);
   r = Nz/Nv;

   dt_old = t(2) - t(1);
   dt_new = dt_old/r;

   t_old = t;
   t_new = dt_new*(0:Nv-1);

   zBP=z.*exp(-1i*2*pi*fc.*t_new);

[S. David]

What if I am doing the resampling P different times, not just once, like:

Ld=max(p./q)*length(v);%Here p and q are vectors of length P
y=zeros(1,Ld);
for cc=1:P
z=resample(v,p(cc),q(cc));
y(1:length(z))=y(1:length(z))+z;
end

Shall I do the above for each (p,q) pair?