[Discuss-gnuradio] Problem with USRP interpolation

[hanwen]

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.

 

I wonder if the sample rate of DAC can be change to mutiple of 2, not 4. In that case, I can set the software interp rate to 2 and interp rate of USRP to 50, for which the burden of interp filter can be reduced.

 

Right now, I have to use 1.3333Mchip/s. The software interp rate of 2 works well. But 1.28Mchip/s is exactly what I want.

 

Thank you ^_^