USRP SDR Warning

This wiki explains the UHD warning that may appear when using USRP SDR cards with Amarisoft eNodeB, especially when the requested interpolation or decimation factor becomes odd. The warning usually does not prevent the eNodeB from working, but it indicates that CIC rolloff may affect the output spectrum, and the sample rate can be adjusted if a cleaner spectrum is required.

When using USRP SDR card, I'm getting a warning that the decimation is odd and that CIC rolloff is expected

When transmitting on bandwidth > 10 Mhz with USRP SDR cards, you may see following message:

[root@xxxx]# ./lteenb config/enb.cfg This software is licensed to me. ... sample_rate=20.000 MHz dl_freq=2117.500 MHz ul_freq=1717.500MHz (band 4) dl_ant=1 ul_ant=1 (enb) UHD: The requested interpolation is odd; the user should expect CIC rolloff. Select an even interpolation to ensure that a halfband filter is enabled. interpolation = dsp_rate/samp_rate -> 5 = (100.000000 MHz)/(20.000000 MHz) *UHD: The requested decimation is odd; the user should expect CIC rolloff. Select an even decimation to ensure that a halfband filter is enabled. decimation = dsp_rate/samp_rate -> 5 = (100.000000 MHz)/(20.000000 MHz)

This is just a warning and the eNodeB can work with it. However, if you want to have the best output spectrum and if the network card is fast enough, you can force the N210 sample rate to 25 MHz with the following additonnal parameters in enb.cfg:

sample_rate: 25, sample_rate_num: 12,

With these parameters you won't get the warning.