[USRP-users] Regarding the 112 decimation and 174 decimation factors

Birhane Alemayoh birhanea at gmail.com
Tue Jun 26 07:10:00 EDT 2012


Hello all

I understand the USB and gigiabit limitation when streaming data to a host
PC. These  RF bandwidth of the FPGA  is decimated by a decimation factor to
reduce the data rate to be streamed to the PC.

For GSM applications, many litratures recommended to use decimation factor
of 112 for USRP1 and 174 for USRP2,  N2xxs to capture one GSM channle. But
how can these decimation factors achieve a bandwidth of one  GSM channel.
One GSM channel has a bandwidth of 200 kHz. But for a USRP N200  with
100MHz sampling rate for example;  if we use 174 decimation factor, we will
end up with 100/174 =  574.7KHz. This will be the input for our PC.
So what is the reason behaind selecting 112 and 174?
Thank you!!

Birhane
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