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Re: [Discuss-gnuradio] Question about latency

From: Firas A.
Subject: Re: [Discuss-gnuradio] Question about latency
Date: Thu, 2 Apr 2009 03:03:46 -0700 (PDT)


Hello everyone, 

I am trying to implement some relaying schemes in gnuradio which require
fast response from 
the relay. I only know how to use flow graphs at the moment so I made my
code with flowgraphs and 
the delay from receiving a packet until I retransmit it is about 10ms. I'm
using USRP1 and the 
sampling rate is 2MSPS and I use the autotransmit capability of USRP. 

First of all I'm trying to understand where the delay comes from. I'm sure
the delay is not due to 
processing time of the packet because the processing is very simple. I don't
know about latencies in 
the kernel though. I read in a paper  that the time it takes for data  to go
from user space to kernel 
is only 200us. 

Secondly I would like to know if using mblocks has any chance of reducing
this delay. By the way is there 
any documentation for the mblocks? 


1) The following page may be useful:

2) Did you tried to increase sampling rate up to 4MHz ?

3) How did you measured the delay ?

Best Regards,


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