It depends on what type of Transfer Function you want to use. For example, if you want to use an ARX model (I am using random inputs and output here, which you can replace with your own data) :
a=arx(iddata(y,x,1),[1 ones(1,16) zeros(1,16)]);
You will need the System Identification toolbox. There are several models which include a transfer function component, such as BJ, ARX, and ARMAX.
Or you can use:
Of course you may want to change the number of poles, zeros, or the delays for each input.