Hi Saurabh,
I have another question about the paper http://nesl.ee.ucla.edu/document/show/153 , figure 11a drift and temperature variation.
We know - "The rate of change of drift is highly correlated with the rate of change of temperature."
But from 4 to 8 hours, the temperature is constant at 18 deg C, but I see lot of drift variations during that period. Why this is so ? I know that drift depends on certain other factors like normal aging of the crystal and mechanical shock. But it is unlikely for a crystal to have much aging effect within 4 hour duration...so what else is causing this variation ?
My next query....drift in figure 11a has been specified as unitless fugures. Are you considering drift as some kind of ratio ? What is that ? I ask this becasue we generally specify drift as parts per million. Datasheets specify drift due to temperature as 20 ppm, I cannot relate your values of -4.428...-4.438 to common notion of drift. Please help me with my doubts.
Thanks a lot for your time,
Smaitra.
.
----- Original Message -----
From: Saurabh Ganeriwal <[EMAIL PROTECTED]> Date: Thursday, March 9, 2006 5:35 pm Subject: Re: [Tinyos-help] Mote Drift >> hi Sharmistha,
>
> I think you are getting confused between the actual error between the
> mote's clocks and the prediction error as used in this paper. Let
> me take
> a stab at clearing out your doubts. Let us represent the clocks of two
> motes by c1(t) and c2(t). Here t represents the real time t, say UTC.
>
> The error between these two clocks at a given time t1 will be
> given by
> c1(t1) - c2(t1). This error can be attributed to many factors such as
> offset in starting the nodes, drift and skew over time. And the worst
> case / average case numbers (assuming no offset) is something that can
> be obtained by the datasheets.
>
> Now, what this paper does is maintain a relative clock model
> between these
> two clocks, some function G(.), i.e. applying G(.) to c1 gives you the
> expected time in c2. The prediction error, as defined in this
> paper and in
> Figure 6 corresponds to
>
> c2(t1) - G(c1(t1)).
>
> No, FTSP does not have that much amount of error. I think you are
> referring to the line in Introduction. By sampling at a lower sampling
> period, FTSP guarantees that the error can never exceed 90
> microseconds.The actual error attained by FTSP will be definitely
> of much smaller
> magnitude.
>
> Please let me know if this is clear. I shall be glad to answer your
> further queries on the paper.
>
> bye,
> saurabh
>
> On Thu, 9 Mar 2006, Sharmistha Maitra wrote:
>
> >
> > Dear All,
> >
> > This is a question about the paper 'Estimating Clock Uncertainty for
> > Efficient Duty-Cyclicng in Sensor Networks', found at
> > http://nesl.ee.ucla.edu/document/show/153
> >
> > The paper entions - 'time prediction error of a sensor node'
> increases> monotonically with 'Sampling Period of time synch
> messages' (figure 6 in
> > paper). I agree that it will increase monotonically, but how did the
> > authors arrive at this graph ? I mean how did they arrive at the
> > particular error values as shown in the graph ? Elsewhere in the
> paper> they have mentioned that FTSP (a quite popular protocol)
> with 1 minute
> > sampling period has prediction error of 90 us. But here in this
> graph I
> > see ~5us error for 1 minute sampling period. By what method has
> this been
> > calculated ?
> >
> > I dont know if this is the right forum to talk about the paper, I
> > apologise if it is not. Anybody who has read this paper, or the
> authors> themselves (if they are in the mailing list), if they can
> clarify , I
> > will appreciate.
> >
> > Thanks,
> >
> > Smaitra.
> >
> > ----- Original Message -----
> >
> > From: Vinayak Naik <[EMAIL PROTECTED]>
> >
> > Date: Thursday, March 9, 2006 12:19 pm
> >
> > Subject: Re: [Tinyos-help] Mote Drift
> >
> > > A relevant paper. http://nesl.ee.ucla.edu/document/show/153
> > >
> > > - Vinayak
> > >
> > > On 3/9/06, Sharmistha Maitra <[EMAIL PROTECTED]> wrote:
> > > >
> > > > Dear All,
> > > >
> > > > I am working on modelling the clock drift of a mote (mica2 )
> > > caused by
> > > > environmental conditions like temperature. Can anybody guide me
> > > where can I
> > > > find any information on this, something like a relation of drift
> > > amount and
> > > > operating frequency ?
> > > >
> > > > My other question- In general we know that mote frequency can
> > > drift by 40
> > > > ppm (natural drift, not due to temperature)....can anybody give
> > > me an idea
> > > > how frequently does this change happen....I mean in the absence
> > > of all
> > > > external phenomenon, approx how long will a mote hold on to its
> > > previous> frequency before 'naturally' jumping off to the next.
> > > All this because
> > > > current literatures suggest that short term stability of the
> > > motes are good.
> > > > What is the extent of this short term ?
> > > >
> > > > Thanks...
> > > >
> > > > Smaitra.
> > > >
> > > >
> > > >
> > > > _______________________________________________
> > > > Tinyos-help mailing list
> > > > Tinyos-help@Millennium.Berkeley.EDU
> > > > https://mail.millennium.berkeley.edu/cgi-
> > > bin/mailman/listinfo/tinyos-help
> > > >
> > > >
> > > >
> > >
> >
>
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