P25 Phase2

DeaconHarry16

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What would be the justification for a system to convert to P25 phase 2 when already invested in phase 1?
I would expect cost of conversion would be a major factor...additional bandwidth possibly?
Just curious,
Thanks
 

n3obl

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Double capacity of RF channels. 2 voice paths vs 1 on single RF channel.
 

GTR8000

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Phase II (TDMA) would instantly double the amount of traffic channels available. Phase I (FDMA) only allows for a single transmission to take place per-frequency, whereas TDMA allows for two transmissions to take place by alternating time slots on the same frequency. The control channel and data channels are always FDMA, so TDMA only applies to voice channels on a P25 system.

If the system is running well with the channel resources it already has licensed and operational, then there's not a whole lot of cost to benefit radio of implementing Phase II. In some parts of the country, frequencies are very hard to come by, and so TDMA is a godsend in being able to do more with less.

There are other technical benefits of TDMA, such as the ability for a radio to receive while transmitting. This works because the radio's transmitter is continuously turning on/off in very short bursts (30 ms) while synced to a voice channel time slot, and so it's both transmitting and receiving in rapid succession. That means that even with the PTT held down, the radio can still receive signaling such as emergencies, and can be preempted by higher priority transmissions or a system console. The radio can also be told to stop transmitting by the control channel if the inbound signal is very poor.
 

jonwienke

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Depends. Many P25 radios are capable of both, so enabling phase II wouldn't necessarily require new hardware.
 

GTR8000

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Depends. Many P25 radios are capable of both, so enabling phase II wouldn't necessarily require new hardware.
Hardware capable, perhaps, but that doesn't always mean it's provisioned. Regardless, at some point TDMA has to be paid for, whether that's on the initial order, or added later on down the road. To provision TDMA on an APX radio, it will cost between $330 to $520 per radio, depending on when and how the feature is added. It's always cheaper when adding options to the original order vs upgrading the radio after the fact, and most states have contract pricing which offers a 25% or so discount.

That's just the subscribers, you still have to take into account the upgrades to the infrastructure to provision TDMA operation. That is not cheap.
 

jonwienke

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$520 is a lot less than the cost of a new radio...
 

DeaconHarry16

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The reason I ask is that i was curious about the long term possibility of our state (WV SIRN) system going to Phase 2...We still have some counties on analog, probably due to cost restraints... I have two well worn Homepatrol 1's that hope will be capable for some time to come...
Thanks for your comments
 

fredva

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Marshall County is currently using Phase 2 on the WV system. I've read that they've been doing some recent work on the towers in the northern panhandle, so providing Phase 2 may have been part of that work. As for the rest of the state, my guess is the state will update the system over time, but one factor will be how quickly agencies replace older radios with new ones. A talkgroup can be Phase 2 capable but if some of the radios actively being used on that talkgroup only operate in Phase 1 mode, then the transmissions will remain Phase 1. As for timing of system upgrades, I would recommend watching the SIRN meeting minutes that are posted in the WV SIRN thread from time to time.
 
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GTR said something very important, in some cases there may not be much of a cost benefit to enable Phase 2 operation on a Phase 2 ready system. Just as some quick examples, Motorola systems have a limitation of how many active voice paths can be simultaneously used for a given setup. This limitation is independent of the system operating in Phase 1 or Phase 2. So enabling Phase 2 on a system that was fully built out on Phase 1...doesn't provide you any additional capacity unless you completely redesign the system and split your fully built out sites into a dual layer configuration (which can be expensive as it requires additional hardware and reconfiguration). Then you have the case of Phase 1 sites which aren't currently running at capacity...if you have a 12 channel system and have only ever used 10 channels simultaneously, going Phase 2 doesn't benefit you until you grow to the point where you are beginning to busy the system out but the decision may be made to make a point of ensuring new subscribers are TDMA enabled if further growth is expected.
 

DeaconHarry16

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I checked out the WV SIEC meeting minutes...looks like they are researching TDMA for areas in the state with dense population.
Being in the southern part of the state i doubt congestion is or will be an issue for the near future.
In their discussions seems like there is also a licensing issue to overcome.
 

kc8iqz

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I checked out the WV SIEC meeting minutes...looks like they are researching TDMA for areas in the state with dense population.
Being in the southern part of the state i doubt congestion is or will be an issue for the near future.
In their discussions seems like there is also a licensing issue to overcome.
Given the growth of the Eastern Panhandle I wonder what will happen to us relative to a move to Phase 2. Any thoughts?
 
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