🚀 go-pugleaf

"Jeremy Quirke" <jquirke@iNOprimSPAMus.com.au> wrote in message
news:3e576c78$0$27372@echo-01.iinet.net.au...
> To add some more information, the GSM timing advance is measured in
> symbol-periods.
>
> The GSM symbol rate for GMSK and 8PSK modulation is 156.25 symbols per
burst
> * 8 bursts per timeslot =frame * 26 frames per 26multiframe (120ms) 270833
> 1/3 symbols per second.
>
> The TA is actually an 8-bit field, not a 6-bit field, however the maximum
> allowable value for DCS1800 and GSM900 is 63 (00111111b).
>
> At 270833+1/3symbols/sec, light (radio) would travel c/[270833+1/3]m, so a
> value of 63 would result in a maximum two-way distance of 63c/[270833+1/3]
=
> ~7x10km (70 kilometres)
>
> The reason for the maximum value of TA is because transmit and receive
> bursting is skewed 3 bursts (Tx 3bursts after Rx). Hence, this leave a gap
> of 468.75 symbol periods, less the TA. The MS has to perform neighbour
> measurements and synchronisation with whatever is left. 63 was chosen to
be
> a reasonable value.
>
> Additionally, I believe the pseudo-synchronised handover scheme may have
> influenced the maximum TA, although I'm not sure. (The psuedo-synchronised
> handover scheme is the most complex handover procedure)
>

It's a little more complicated than that.

> --Jeremy Quirke
>
|; )
>
>
> "John Henderson" <jhenRemoveThis@bigpond.com> wrote in message
> news:b334e9$1fo3ki$1@ID-83062.news.dfncis.de...
> > "Pascal" wrote:
> >
> > > I am considering that option to gain reception in remote areas.
> > > Anyone with on mounted on his car ?
> >
> > Yes.  I've tried various, and find a high-gain whip antenna the
> > best.  But get one that's wired from phone to antenna - not an
> > RF-coupled "through the glass" one.  A whip aerial is
> > omnidirectional (if it's not physically obstructed).
> >
> > > What is the maximum gain I can expect ?
> >
> > > I have seen 7dB and if my memory is good from uni, it means 4
> > > times better as it doubles every 3 decibels.
> >
> > I've tried various from 3 to about 5, and find the 5 excellent.
> >
> > Bear in mind that you're limited by Timing Advance (TA) in a GSM
> > phone.  This is the compensation made for the delay caused by the
> > speed of light, to ensure that the bursts transmitted by your
> > phone get to the tower at exactly the right time for
> > synchronisation with your allocated timeslot.
> >
> > It's a 6-bit field, so values range from 0 to 63.  At 553.5
> > metres per step, that gives GSM an absolute maximum range of 35
> > km.
> >
> > There's a workaround to this limitation, using pairs of timeslots
> > in half-capacity cells.  Extended Range, and Enhanced Extended
> > Range cells have maximum ranges of 72 and 121 km respectively.
> > But they're rare.  In general, you might "see" cells further then
> > 35 km away, but you won't be able to use them.
> >
> > > I have found some Omnidirectional antenna designed for both GSM
> > > and GPS.
> > > Is that a better alternative to the vertical antenna ?
> >
> > If these are the compact, stick-on, "phased array" types, I've
> > found them reasonably good, but whip antennae better.
> >
> > John
> >
> >
>
>