Tetra TDM maximum tower range limit?

[wlmr]

Is there a limit to how far from a tower a Tetra portable/mobile can be? I read something quite a while back that seemed to indicate that TDM has a finite limit in how much time a radio in the field has to get back into the system before the signal collides with the next time slot. Am I anywhere close in my understanding of how a Tetra system works - ie., is it a TDM system? Do you have to put in another tower to cover a longer distance?

[smr]

Originally Posted by wlmr

Is there a limit to how far from a tower a Tetra portable/mobile can be? Do you have to put in another tower to cover a longer distance?

Yes, there is a limit.
35 km in normal configuration and 72 km in AGA mode.
So if you want to cover a longer distance you simply just have to install a new basestation.

[citylink_uk]

That's the theorical maximum possible range but on a real world network with a 3W limited mobile radio, i'd guess at around 5 or 6 miles.

Rich

[smr]

Originally Posted by citylink_uk

That's the theorical maximum possible range but on a real world network with a 3W limited mobile radio, i'd guess at around 5 or 6 miles.

Rich

Well, last week I was able to to log into tetra network with a handheld device over the distance of 70 km. Well, the 70 km was sea but still, the figures in my last post are quite realistic for a "real word" 2W mobile radio. Max 12-14 km for a handheld in a rural landscape.

[N_Jay]

RF range depends on the power, antenna, terrain and desired reliability.
This is true for all systems, TETRA has no advantage over any other technology implemented with the same power on the same band.

The distance limitation of the protocol is due to the acceptable time window for a field unit to respond to a outbound command. Most trunking and cellular protocols have a similar limit (from a technical perspective), the specific distance/time limitations are different for each protocol.

[wlmr]

Originally Posted by N_Jay

TETRA has no advantage over any other technology implemented with the same power on the same band..

I agree on the no advantage! On the contrary, this may be the info I heard quite ago as a reason that TETRA is a problem for large areas. Rather than installing a land mobile radio system with fewer sites, it seems to be closer related to installing a phone system with lots of sites($). I'd hate to see what the cost would be to put in a statewide system that covers rural areas this way. Michigan, Colorado, South Dakota, and Wyoming immediately come to mind - both VHF and 800 MHz systems.

Originally Posted by N_Jay

The distance limitation of the protocol is due to the acceptable time window for a field unit to respond to a outbound command. Most trunking and cellular protocols have a similar limit (from a technical perspective), the specific distance/time limitations are different for each protocol.

I'll have to see if I can find some info on the trunking system near me. The distance numbers given above seem pretty puny compared with the distances I'm estimating are being covered here.

Thanks everyone for the responses!

[N_Jay]

Originally Posted by wlmr

I agree on the no advantage! On the contrary, this may be the info I heard quite ago as a reason that TETRA is a problem for large areas. Rather than installing a land mobile radio system with fewer sites, it seems to be closer related to installing a phone system with lots of sites($). I'd hate to see what the cost would be to put in a statewide system that covers rural areas this way. Michigan, Colorado, South Dakota, and Wyoming immediately come to mind - both VHF and 800 MHz systems.

Yep, it is much like a cellular system where both capacity and coverage are addressed with additional sites. The goal is to be able to hand over before you get near the threshold of coverage.
This is very different than traditional LMR design.

TETRA is not that different than iDEN, and look at the issues Nextel had (even in its heyday) covering rural areas.

Originally Posted by wlmr

I'll have to see if I can find some info on the trunking system near me. The distance numbers given above seem pretty puny compared with the distances I'm estimating are being covered here.

Where is "here"?
If you are talking about the US, Smartnet and other 3600 BPS Motorola systems generally had a 75 mile range, but there was a modification to give you 100 miles range, but then the site would generally not respond to a unit less than 25 miles.
It was for tall mountain top use.

It is all about timing. I don't recall what the windows are for EDACS and P25, but anyone who knows the protocol at the bit and frame level can figure it out.

[wlmr]

Here is trunked P25 Simulcast. (US) The same frequencies are used at each it's subsites instead of figuring out frequencies for each site that don't interfere with their neighbors. Much more efficient way of covering an area without either a massive pocketful of frequencies or limiting how many frequencies each site can have. Also cuts down on hand-offs from site to site. There's also a couple of standard trunked sites on the edge to get a bit further our in a couple of directions where the load isn't as great.

Been a while since I was taught the spec's for either the system or radios, but 30 miles isn't a problem at all as long as there aren't obstructions. The simulcast site has a big footprint on it's own, and the remote sites in particular seem to show up in unbelievable locations.

[N_Jay]

P25 Trunked (and Smartnet.SmartZone, EDACS, etc.) can do both simulcast and multi-site (almost cellular with big cells).
Each is used depending on a lot of factors including the coverage needed, channels available, and typical group communications model.

TETRA is cellular architecture only.

[Raccon]

The theoretical limit for non-AGA sites is 58km, for AGA sites at least 80km.

From the TETRA standard ETSI EN 300 392-2 V3.2.1 (2007-09), O.2 Air - Ground - Air service overview:

The path delay due to the air cell size may exceed normal system capabilities and clause O.5 define optional modifications to the air BSs and MSs to support longer path delays allowing distances at least to 80 km.

NOTE 2: Based on the specifications in clause 6.4.5 the maximum allowable path delay for a normal TETRA burst structure is 7 symbols (i.e. 14 bits equivalent to the guard period at the end of uplink timeslot). Each symbol represents a distance of 8,33 km giving a total maximum cell radius of 58 km.