Re: Comparing phase of physically distant signals

From	Don Y <this@isnotme.com>
Newsgroups	comp.arch.embedded, comp.realtime
Subject	Re: Comparing phase of physically distant signals
Date	2013-08-03 11:56 -0700
Organization	Aioe.org NNTP Server
Message-ID	<ktjjpf$ono$1@speranza.aioe.org> (permalink)
References	<kticf7$hg3$1@speranza.aioe.org> <YC3Lt.27237$hO6.14194@fx20.am4> <5ikpv8dj2h34l1d8j5loqmbhht12v9b9j5@4ax.com>

Cross-posted to 2 groups.

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Hi,

On 8/3/2013 3:21 AM, upsidedown@downunder.com wrote:
> On Sat, 03 Aug 2013 09:58:31 +0100, Tom Gardner
> <spamjunk@blueyonder.co.uk> wrote:
>
>>> [posted to S.E.D in the hope that a hardware analog might exist]
>>>
>>> I synchronize the "clocks" on physically distributed processors
>>> such that two or more different machines can have a very finely
>>> defined sense of "synchronized time" between themselves.
>>>
>>> During development, I would measure this time skew (among other
>>> factors) by locating these devices side-by-side on a workbench
>>> interconnected by "unquantified" cable.  Then, measuring the
>>> time difference between to "pulse outputs" that I artificially
>>> generate on each board.
>>>
>>> So, I could introduce a disturbance to the system and watch to
>>> see how quickly -- and accurately -- the "clocks" (think FLL and
>>> PLL) come back into sync.
>>>
>>> How do I practically do this when the devices are *deployed*
>>> and physically distant (vs. "electrically distant" as in my
>>> test case)?
>>>
>>> Two ideas come to mind:
>>> 1) two equal length cables to connect the "pulse outputs"
>>> from their respective originating devices to the test gear.
>>> 2) two *radios* to do the same thing -- after accounting
>>> for different flight times
>>>
>>> [Though I wonder how hard it is to qualify two different
>>> radios to have the same delay, etc.  Far easier to trim
>>> two long lengths of wire to the same length!]
>>>
>>> Of course, I would like to minimize the recurring cost of
>>> any solution as it is just present for system qualification
>>> (and troubleshooting) and offers no run-time advantage to
>>> the design.
>
> Have you studied NTP and IEEE 1588-2008 ?

Yes.  The protocol I designed is a bastardized version of PTP
(1588)  [Because I don't have to coexist with COTS devices and
can thus exploit this fact to make the protocol "less expensive"
for a given level of resources]

>> This whole question smacks of one of those questions
>> that ought to be "unasked".
>>
>> The concept of having "as single time everywhere" is
>> erroneous in general, but under limited circumstances
>> there are useful approximations.
>
> Agreed when thinking of the theory of relativity.

I am willing to ignore relativistic effects on the scale
of a city block  :>

>> You do not give enough
>> information to indicate whether the approximations
>> would be valid and/or useful.
>
> For ground bound or slowly moving (v << c) this should not be a
> problem as long as the locations of the stations or at least the
> distance to a common source is known.

But you wouldn't know those distances -- unless you *measured*
them.  (By contrast, two equal lengths of wire can be previously
constructed)

>> If the time-of-flight of messages between the two
>> ends is much less than the time resolution to which
>> synchronisation is required, then effectively a
>> "single time" /is/ possible. Otherwise, not.

The ToF can differ as long as the difference is known
(or can be known and compensated)

>> Reduce the distances, and similar principles apply
>> with smaller time differences.
>>
>> As a separate issue, non-line-of-sight radio channels
>> are continuously varying in length and thus in propagation
>> delay (and even LoS ones to a lesser extent). Ask
>> any ham, or consider how multipath is *required* for
>> cellular phone systems.
>
> If the response is sent back at _exactly_ the same frequency, the
> propagation delay is the same in both directions and hence satisfy the
> NTP approximation in both directions. However, if a duplex system is
> used, using different frequencies for the up- and downlink, the
> multipath pattern might be quite different and the NTP equal
> propagation delay assumption do not apply.

No, I'm not looking at putting this *in* the (control) loop.

Rather, I have two (multiple) devices who are synchronized
(whatever that means).  They are physically separated by distances
that make comparing reference "synthesized events" (i.e., a pulse
on a particular conductor) on each device to each other via
some piece of test kit.

I.e., on a test bench, I can put any number of such devices
separated by long, uncalibrated lengths of wire (network cable)
and verify/quantify the degree of synchronization by locating
them within inches of each other (i.e., so I can use a pair
of probes connected to a single piece of test equipment).

How does someone do that when the devices are *deployed* and
all that interconnect cable represents *physical* distance?

Thread

Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 00:45 -0700
  Re: Comparing phase of physically distant signals Jan Panteltje <pNaonStpealmtje@yahoo.com> - 2013-08-03 07:51 +0000
  Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 09:58 +0100
    Re: Comparing phase of physically distant signals upsidedown@downunder.com - 2013-08-03 13:21 +0300
      Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 12:16 +0100
      Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 11:56 -0700
        Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 20:17 +0100
          Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 13:41 -0700
            Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 22:46 +0100
              Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 14:57 -0700
                Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 23:09 +0100
    Re: Comparing phase of physically distant signals upsidedown@downunder.com - 2013-08-03 13:58 +0300
      Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 12:30 +0100
    Re: Comparing phase of physically distant signals upsidedown@downunder.com - 2013-08-03 16:08 +0300
      Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 14:22 +0100
        Re: Comparing phase of physically distant signals upsidedown@downunder.com - 2013-08-03 16:38 +0300
          Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 10:46 -0700
      Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 10:40 -0700
        Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 20:04 +0100
        Re: Comparing phase of physically distant signals Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2013-08-04 15:55 +0200
          Re: Comparing phase of physically distant signals upsidedown@downunder.com - 2013-08-04 19:42 +0300
            Re: Comparing phase of physically distant signals Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2013-08-04 21:08 +0200
              Re: Comparing phase of physically distant signals upsidedown@downunder.com - 2013-08-05 15:28 +0300
                Re: Comparing phase of physically distant signals Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2013-08-05 22:17 +0200
                Re: Comparing phase of physically distant signals Richard Damon <Richard@Damon-Family.org> - 2013-08-05 23:20 -0400
    Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 14:26 +0100
    Re: Comparing phase of physically distant signals George Neuner <gneuner2@comcast.net> - 2013-08-03 14:47 -0400
  Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-03 08:17 -0700
    Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 12:08 -0700
      Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 20:37 +0100
        Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 12:57 -0700
          Re: Comparing phase of physically distant signals Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2013-08-04 15:58 +0200
      Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-03 12:44 -0700
        Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 18:36 -0700
          Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-04 09:56 -0700
            Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-05 14:53 -0700
              Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-05 15:38 -0700
                Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-07 01:25 -0700
                Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-07 08:06 -0700
                Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-07 09:21 -0700
  Re: Comparing phase of physically distant signals josephkk <joseph_barrett@sbcglobal.net> - 2013-08-03 15:40 +0000
    Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-03 10:05 -0700
      Re: Comparing phase of physically distant signals John S <Sophi.2@invalid.org> - 2013-08-03 12:13 -0500
        Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-03 10:26 -0700
          Re: Comparing phase of physically distant signals John S <Sophi.2@invalid.org> - 2013-08-03 12:51 -0500
            Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-03 11:54 -0700
              Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 20:27 +0100
                Re: Comparing phase of physically distant signals George Neuner <gneuner2@comcast.net> - 2013-08-05 03:26 -0400
                Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-05 10:34 +0100
                Re: Comparing phase of physically distant signals Richard Damon <Richard@Damon-Family.org> - 2013-08-05 23:29 -0400
                Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-06 08:53 +0100
          Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 12:49 -0700
        Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 12:34 -0700
      Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 12:18 -0700
        Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-03 12:52 -0700
          Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 13:21 -0700
            Re: Comparing phase of physically distant signals Jeff Liebermann <jeffl@cruzio.com> - 2013-08-03 13:31 -0700
              Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 14:46 -0700
                Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-03 15:03 -0700
                Re: Comparing phase of physically distant signals Jeff Liebermann <jeffl@cruzio.com> - 2013-08-03 17:25 -0700
            Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-03 14:50 -0700
    Re: Comparing phase of physically distant signals "Paul E. Bennett" <Paul_E.Bennett@topmail.co.uk> - 2013-08-04 11:06 +0100
      Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-04 12:19 -0700
  Re: Comparing phase of physically distant signals John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> - 2013-08-03 11:47 -0700
  Re: Comparing phase of physically distant signals Richard Damon <Richard@Damon-Family.org> - 2013-08-03 18:23 -0400
  Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-05 16:53 +0100
    Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-05 13:19 -0700
      Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-06 00:27 +0100
        Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-05 20:09 -0700
          Re: Comparing phase of physically distant signals Paul Rubin <no.email@nospam.invalid> - 2013-08-05 22:12 -0700
            Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-06 09:12 +0100
            Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-06 01:47 -0700
              Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-06 10:08 +0100
                Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-06 02:25 -0700
                Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-06 02:48 -0700
                Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-06 10:49 +0100
                Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-06 03:06 -0700
                Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-06 11:57 +0100
                Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-06 10:28 -0700
                Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-06 21:52 +0100
                Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-07 01:34 -0700
                Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-07 09:46 +0100
              Re: Comparing phase of physically distant signals Les Cargill <lcargill99@comcast.com> - 2013-08-06 07:22 -0500
                Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-06 10:42 -0700
                Re: Comparing phase of physically distant signals Les Cargill <lcargill99@comcast.com> - 2013-08-06 23:04 -0500
                Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-06 23:50 -0700
                Re: Comparing phase of physically distant signals Les Cargill <lcargill99@comcast.com> - 2013-08-07 13:05 -0500
                Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-07 18:22 -0700
                Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-08 09:35 +0100
              Re: Comparing phase of physically distant signals Paul Rubin <no.email@nospam.invalid> - 2013-08-06 22:18 -0700
                Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-07 03:09 -0700
                Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-07 12:39 +0100
                Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-07 13:18 +0100
          Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-06 09:23 +0100
            Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-06 02:02 -0700
          Re: Comparing phase of physically distant signals "Paul E. Bennett" <Paul_E.Bennett@topmail.co.uk> - 2013-08-06 09:49 +0100
            Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-06 02:17 -0700
  Re: Comparing phase of physically distant signals Paul E Bennett <Paul_E.Bennett@topmail.co.uk> - 2013-08-16 21:07 +0100
    Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-16 14:50 -0700
      Re: Comparing phase of physically distant signals Paul E Bennett <Paul_E.Bennett@topmail.co.uk> - 2013-08-18 19:55 +0100
        Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-19 11:43 -0700
          Re: Comparing phase of physically distant signals Paul E Bennett <Paul_E.Bennett@topmail.co.uk> - 2013-08-20 21:43 +0100
            Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-20 14:49 -0700

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