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Re: [Discuss-gnuradio] Latency measurement using GnuRadio

From: Ed Criscuolo
Subject: Re: [Discuss-gnuradio] Latency measurement using GnuRadio
Date: Thu, 10 Sep 2009 14:39:28 -0400
User-agent: Thunderbird (Macintosh/20081105)

The short answer is, because our customers require it!

The longer answer is that these are strictly low-earth-orbit
spacecraft, communicating through a relay in geosync.  So,
the round-trip time is dominated by the round-trip time to
geosync, which is around 250 mS.  The new modems include all
sorts of fancy signal processing, including LDPC error correction
and direct-sequence spread spectrum.  So their processing time
could easily become significant.

The whole system has an overall latency budget, and a portion of
it is allocated to the modems.  They're being built out-of-house,
so we need to be able to verify their performance when we do
acceptance testing.

@(^.^)@  Ed

address@hidden wrote:
OK, so I'm being a smartass, but why do you care about latency on a path whose 
path length may be anywhere from a few 10s of milliseconds, to
  several hours?

------- Original Message -------
From    : Ed Criscuolo[mailto:address@hidden
Sent    : 9/10/2009 1:38:07 PM
To      : address@hidden
Cc : Subject : RE: [Discuss-gnuradio] Latency measurement using GnuRadio

 Hi all.

   At work we're building some new modems for spacecraft communication,
and I've been tasked with coming up with a test set or tool for
measuring latency through each side of the modem (modulator and

   I'd like to use GnuRadio 2 and a USRP2 to do some or all of this.

I was wondering if the sample time-stamping capability was fully functional in version 2, and if I could use it to insure that a given
sample was transmitted at a specific time.  Similarly, can I get time
stamps on received samples?


@(^.^)@  Ed

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