Re: [Discuss-gnuradio] Problem with USRP interpolation

[Matt Ettus]

hanwen wrote:

> Hi,
>  
> Recently, I'm trying to do CDMA commnication at 1.28Mchip/s with USRP 
> and I've met a problem.
> The sample rate of DAC on USRP is 128M, so samples avialabe for each 
> chip is 128M / 1.28M = 100.
> The interpolation rate of USRP must be [4, 512] and multiple of 4. So 
> the only choice for me seems to be setting the software interpolation 
> rate to 5 and the interpolation rate of USRP to 20 (multiple of 4). 5 
> * 20 = 100. But the software interp is still too high for the 
> root_raise_cosin interp filter (interp=5, len(taps)=16), and a lot of 
> "Uu" comes out. However, the software interp cannot be reduced further.
>  


The other option is to figure out why this isn't running fast enough.  
Is the USB bus too slow or is it your processor?  What sort of processor 
are you using?  You shouldn't have any problem at this data rate.

Try this:

usrp_siggen.py -d 20

If that underruns, your USB bus is not fast enough.  Otherwise it is 
your processor.

Matt