28 Sep
2016
28 Sep
'16
1:14 a.m.
Hi all:
Phase II uses TDMA. As I understand it, the radios need to constantly
adjust their internal clocks as they move towards and away from the
base station to stay in sync with their assigned time slot.
If you're running a USRP in your house, and your house is not located
in precisely the same location as the base station, wouldn't the
time slots of the radios tend to blend together, making it impossible
to listen to their transmissions?
--
Alex
28 Sep
28 Sep
1:45 a.m.
That is a very interesting question, there is some margin built in to the timing specs,
but it's not clear how much the time difference of arrival would eat into that.
It's usually not that common or easy to monitor mobiles directly in UHF/800/900 - the
much more common case is to listen to them via the repeater output (downlink) anyway, also
TDMA isn't currently used for direct (simplex) mobile/mobile comms.
The trunking RX in OP25 does support P2/TDMA, but only to listen to repeater downlinks.
There are different modulation formats for uplinks and downlinks.
1:54 a.m.
On 27 Sep 2016 16:45:11 -0700
"ikj1234i(a)yahoo.com [op25-dev]" <op25-dev(a)yahoogroups.com> wrote:
That is a very interesting question, there is some
margin built in to
the timing specs, but it's not clear how much the time difference of
arrival would eat into that. It's usually not that common or easy to
monitor mobiles directly in UHF/800/900 - the much more common case
is to listen to them via the repeater output (downlink) anyway, also
TDMA isn't currently used for direct (simplex) mobile/mobile comms.
Wouldn't that make multilateration of P25 phase II handsets impossible,
since it's entirely predicated on measuring TDOA? Or is the guard
interval sufficiently long enough that it doesn't matter at short
distances?
--
Alex
2775
days inactive
2775
days old
2 comments
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participants (2)
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Alex alex323＠gmail.com [op25-dev] -
ikj1234i＠yahoo.com [op25-dev]