Re: [Discuss-gnuradio] Sampling rate in USRP 1

[Johnathan Corgan]

On Thu, May 30, 2013 at 7:51 AM, Karan Talasila <address@hidden> wrote:

 

    I am using USRP 1 for an application. I am using complex baseband representation, so i am setting bandwidth almost equal to the sampling rate. But many times i see that when i set the sample rate I get target sampling rate is different from actual sampling rate. I checked the wiki, it says 64Msps/N should be an integer. How should i decide the value of N so that the division is an integer. what is the significance of N?

Secondly I have a doubt on samples/symbol. If I use complex baseband and say bpsk modulation, i set bits/symbol as one. should i set samples/symbol as 2 as there is one sample in I and one in Q. So is it default 2 samples/symbol or does it depend on anything else.

Karan,

In all discussions regarding complex baseband, a "sample" is counted as a single complex number, not separate I and Q samples (though with the USRP, I and Q are in fact sampled with separate ADCs in synchrony.)

Regarding the configuration of the USRP1, the sample rate must be an integer fraction of 64Msps, and also less than or equal to 8 Msps due to the speed limitation of the USB 2.0 bus.  N in this case is that integer; however, you don't need to specify this, but rather the resulting sample rate.  The way the wiki page is written is probably a hold over from the (very) old, discontinued USRP blocks in GNU Radio, which did take N as a parameter.

With BPSK modulation, depending on the technique you are using for matched filtering and timing recovery, you may want to set your initial receive rate to greater than one sample per symbol.

-- 
Johnathan Corgan

Corgan Labs - SDR Training and Development Services
http://corganlabs.com