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?
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.
On 27 Sep 2016 16:45:11 -0700 "ikj1234i@yahoo.com [op25-dev]" op25-dev@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?
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Alex alex323＠gmail.com [op25-dev] -
ikj1234i＠yahoo.com [op25-dev]