Re: [Discuss-gnuradio] question on gmsk mod block

[Matt Ettus]

Anastasopoulos Achilleas wrote:
> Hi,
>
> I noticed that the Gaussian pulse is convolved with a rectangular window
> in the GMSK modulator. Why is that so?

The pulse is convolved with a rectangular window because the incoming 
data is not. 

For example, if you wanted to send 1011 and had 4X interpolated data, 
the data stream into the gaussian filter would look like:

1,1,1,1,-1,-1,-1,-1,1,1,1,1,1,1,1,1

however, the input to the block in question is:

1,0,0,0,-1,0,0,0,1,0,0,0,1,0,0,0

It was easier to precombine the zero-order hold with the gaussian filter 
by convolving it rather than having 2 separate filters in the real-time 
portion of the code.

Matt