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  #21 (permalink)  
Old 01-25-2013, 1:20 PM
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@902..The only TETRA systems working are over seas.. So a comparison to OPENSKY is not an apples to apples comparison.. There are several WORKING OPENSKY systems that do as they were designed to do.. Jersey Transit could be another "working" system if they follow the site requirements and do as they are asked..
Each failed OPENSKY system has not had the number of sites required to hold the amount of traffic the system was designed to handle..

Another key point to any system, If it doesn't sport a bat wing, IT"S JUNK.. Ask any firefighter or cop..

Just my .02
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  #22 (permalink)  
Old 01-25-2013, 3:54 PM
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Quote:
Originally Posted by dcr_inc View Post
@902..The only TETRA systems working are over seas.. So a comparison to OPENSKY is not an apples to apples comparison.. There are several WORKING OPENSKY systems that do as they were designed to do.. Jersey Transit could be another "working" system if they follow the site requirements and do as they are asked..
Each failed OPENSKY system has not had the number of sites required to hold the amount of traffic the system was designed to handle..

Another key point to any system, If it doesn't sport a bat wing, IT"S JUNK.. Ask any firefighter or cop..

Just my .02
Well... I have fought the "I only love THIS manufacturer" battle and I have tested a number of alternatives, some really good, some really bad (sometimes from the same manufacturer). Yes, there is that bias out there, but I will say that some of the other manufacturers are learning their lesson and coming out with things that are just as good - if not better and with less strings attached. The split that resulted in Solutions and Mobility was pretty telling, and, land mobile radio is almost a hobby to a company that makes satellite command and control systems. It's undeniable, really.

I mentioned OS and "work" in quotes because it seems to be bashed in a number of instances, but NOBODY can ever provide a cogent reason for why it "fails," until you. Your reason makes sense. In years of following PA, NYS, and an implementation in South Florida, no one's ever been able to pin the tail on that donkey. I can't imagine it would continue to be a supported product if there were major issues that no one knows about. I DO imagine that both vendors and the procurers try to hack down prices to the point they've impaired their systems. I've had several vendors low-ball things to me, hoping that I would go on a supplemental binge-buy at some future point after I've gotten married to them and their product. Not saying that's the case, but it's out there.

A transit system can be built for vehicular on-the-street coverage, so the number of sites can be reduced. It wouldn't necessarily be satisfactory for portable coverage in areas where it's not deliberately engineered.

Please tell me more about your experiences with OpenSky! I've used it once; I pushed the button, spoke, someone answered me, and that was that. Audio sounded a little compressed, but it seemed to work fine for me. Really, 4/TDMA is 4/TDMA, nothing magic about it.
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Old 01-28-2013, 11:43 AM
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I've been casually following the thread and I suppose it's time to jump into the fray. The unstated reason for why TETRA is more beneficial than other technologies is talkpath gain. For one 22 kHz wide channel (a 20 kHz channel for PowerTrunk's "reduced power" TETRA), you get 4 talkpaths. For one repeater station, you have 4 timeslots that can be each used for a separate conversation or data transaction.
Not entirely correct, TETRA uses 1 timeslot for the control channel which cannot carry any voice, only messages of the Short Data Services (SDS) but not packet data (PD), so one carrier (= 1 frequency pair) provides a maximum of 3 timeslots for voice and/or packet data.
The maximum number of carriers for one TETRA base station is 8, so you can have up to 31 timeslots for voice and/or packet data on a single site. Some vendors also offer secondary control channels (SCCH) or dedicated control channels (DCCH) where heavy SDS traffic is required/expected, which then take away an equal amount of timeslots from voice or PD traffic (how many is configurable).

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There is a caveat - P25 Phase II still relies on a dedicated control channel, so one repeater is dedicated to 9.6 kbps signaling and control. A three repeater P25 Phase II system allows for 4 talkpaths, not 6. A three repeater TETRA system allows for 12 talkpaths.
11 (3x4-1).
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Old 01-28-2013, 3:38 PM
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Thank you! I love to learn!
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  #25 (permalink)  
Old 02-13-2013, 3:15 PM
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Actually each TETRA base station can carry up to 32 carriers in theory.

Each carrier 4 slots but minimum 1 Main Control Channel per site. Although frankly speaking if you need so many carriers it is because there are lots of radios so you would need secondary control channels to manage all the radios.

A good assumption to make is made is that minimum each 8 carriers you need 1 control channel so for each 8 carriers will give you: 31+1 slots
Then for a 32 carrier site: 124+4.

You can imagine a system with 127 radios that are in call 24/7, then you will need a 32 site carrier but only 1 Control Channel is enough for controlling all of the radios.
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Old 02-14-2013, 1:37 PM
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Originally Posted by Radiobec View Post
Actually each TETRA base station can carry up to 32 carriers in theory.
I am curious, where do you get the 32 from?
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  #27 (permalink)  
Old 02-14-2013, 3:32 PM
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32 is maximum per base station which is documented by a few of the manufacturers
PowerTrunk: PowerTrunk TETRA Infrastructure System
Motorola: http://www.oppermann-telekom.de/pdf/...-datasheet.pdf
DAMM:http://www.dancom.com.my/biz_division/pdf/bs411.pdf

I'm sure you can find more.

As a real life example, Schipol Airport in Amsterdam has a TETRA network by Rohill. This is Single Site deployment with 16 carriers and handles 7000 radios simultaneously on the system.
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Old 02-15-2013, 6:49 AM
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Default Transit Tetra

This is going to be one hell of a great system if it works out the way they are proposing and desiging it to be
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Old 02-15-2013, 8:31 AM
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Quote:
Originally Posted by Radiobec View Post
32 is maximum per base station which is documented by a few of the manufacturers
PowerTrunk: PowerTrunk TETRA Infrastructure System
Motorola: http://www.oppermann-telekom.de/pdf/...-datasheet.pdf
DAMM:http://www.dancom.com.my/biz_division/pdf/bs411.pdf

I'm sure you can find more.

As a real life example, Schipol Airport in Amsterdam has a TETRA network by Rohill. This is Single Site deployment with 16 carriers and handles 7000 radios simultaneously on the system.
Thanks. Quite surprising to use that many carriers since the losses of the combiner system must be quite high.
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  #30 (permalink)  
Old 02-15-2013, 8:48 AM
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There is really no question that technically, TETRA is more efficient in spectrum and equipment space usage than P25. About the only thing holding TETRA back right now is that it still does not have a VHF offer which is necessary to really succeed in the North American market. That and the incumbent P25 vendors....

Regarding 32 or even 16 carriers I agree that that many carriers is quite high and and I would say is not the typical deployment, but it is possible and as such is a viable option when needed.
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  #31 (permalink)  
Old 05-08-2013, 8:21 AM
   
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I do not want to go over what has been previously said (technically aspects - not enough time/space on the forum), but having been designing/engineering TETRA for past decade and coming from RBOC RF engineering cellular (GSM/CDMA/LTE), the US public safety officials are clueless about this technology. They think P25 and LTE is going to save them. Comparing TETRA/TEDS to P25 (I or II) is like comparing Family Radio Service to PMR. There is no comparison other than they are both communication devices. P25's are basically "dumb" terminals. When you compare feature sets, capabilities, software APS and the numbers networks deployed world-wide (approx 140+), there is no comparison. ETSI made sure it was an open standard. Any authorized terminal will work on any TETRA network (same spectrum). There is less discrepancy among manufacturers, that is, the equipment is all quite good. Motorola (UK), EADS (Cassidian), Siemens, Sepura (UK), SELEX (Italy), PowerTrunk (Celtronics/Spain), Hytera (China). Infrastructure from Rohill (German), DAMM (Netherlands). Lots of independent support firms. Any OpenSky (25 KHz) is a great fit (spectrum). TETRA would be an answer to the nationwide public safety if we would open/modify our regulatory and provide spectrum. There is federal spectrum in the 425 MHz range that has been used in the past. The government could find spectrum but lobbyists and political pressures have made it not happen. TETRA cannot be not designed like a traditional LMR, if so, it will fail. There are few consultants able to do it properly. I know P3 Com (Germany/NJ) and Martin (out of Boston) both have extensive experience with TETRA. TETRA is very dynamic and we are several generations since 1996. I know A/Lucent is the PM for NJ Transit. This could go very right or very wrong. If it is designed/engineered/implemented correctly, it will shine; if not, it will sink quickly to the bottom . . .
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Old 05-08-2013, 12:54 PM
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I should have checked this thread more often, but it didn't flag in my queue until today.

On the statement of TETRA not having any VHF offerings in the US, such implementation would be calamitous. Keep in mind that VHF allotments in the United States are inefficient at best and are assigned in 7.5 kHz channel increments along with what is predominately 11.25 kHz occupied bandwidth, making adjacent channel coexistence impossible without interaction. As such, the adjacent channel reuse here is predicated on geographic separation. Having a 22 kHz wide occupied bandwidth in VHF would consume a number of channels and have co-channel and adjacent channel implications for all -- even though the user may have migrated from a 20K0 analog occupied bandwidth. The channel occupancy pattern also changes, as emitters will remain in transmit for much longer periods of time (possibly continuously?). We see this already with other TDMA emissions, and that does not share well in non-exclusive spectrum.

Also, VHF is unpaired here. Combinations of inputs and outputs are chosen at random and it is extremely common for someone's system input to be the system output of another licensee. It's a disaster that has taken 50 years of random assignment to achieve. VHF TETRA deployment would require greenspace first. We have some of that from supplanted technologies, but such is usually hoarded for real estate value and lies fallow in the hands of auction winners.

There is a category of stakeholder proponent here, more likely shareholders, who are aggressively promoting LTE as visionary. While it has its uses, actual practitioners are more realistically skeptical. The proponents tend to be C-level individuals who are more IT-based than have come up through radio, and public safety retirees (or soon-to-bes) who are far removed from daily operations. As for P25, it has taken on a life of its own and seems to have failed to embrace market share for all but the largest systems. So, I'm not sure the door is closed by anyone but marketers and lobbyists. Frankly, TETRA has not taken off in the U.S. because access to it has been artificially denied based on various intellectual property claims and deliberate choice to refuse the market. There very well may also be some user bias.

As far as it shining, there is a lot at stake in a first-of-a-kind implementation. I'm sure concerned people are moving planets to make it work, if they can, and I see no reason why it won't.
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  #33 (permalink)  
Old 05-08-2013, 2:43 PM
   
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I agree for the most part. VHF will be offered in 2014. Tough to do for US market unless some enterprising investor seeks out the Part 22 going to auction I believe in July. These are 30 KHz generally paired channels.
I thought the NATF would bid, but I have seen no sign of the pre-bid requirement. The problem is being 4 slot and further organized into 18 frames (multframe length both V+D) which is compressed and conveyed in really 17 frames thus allows the 18th to be the control frame without screwing up the data flow. This allows the SACCH to be the background control channel being present even in heavy traffic. Nice feature. As far as occupied bandwidth, PowerTrunk modified (in the US) their mask to reduced the bandwidth - something I personally do believe was required, but being linear, it was a realistic concern. I especially like ACELP running at the 4.8 kbit/s which provide decent voice recovery and noise suppression. We could continue, but I am a TETRA fan and having used/engineered both systems (P25 & TETRA) there is no contest. In fact, even Motorola (Tom Q. of UK) feels it is the mission critical choice. I guess you do not know how an Aston Martin drives until you actually drive one. The US can keep their Crown Vics.
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Old 05-08-2013, 3:43 PM
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For what it's worth, there is at least one FCC application currently pending.

Sites at: Allenwood, Paterson, Cherryville, Cranford, South Amboy, and Plainsboro. Frequencies: 854.2375, 854.2875, 854.5625, 854.6125, 854.8375, 855.8375, 856.2375, 856.4875, 856.5375, 857.2375, 857.4875, 857.5375, 857.6875, 858.0125, 858.2375, 858.4875, 858.6125, 859.0125, 859.2375, 859.4875, 859.5125; it looks like all 22 at each repeater site. Emissions designators 22K0D7D, 22K0D7E, 22K0D7F.

I haven't scoured the application in depth, above info is at a glance. I came upon it while doing a periodic check for just one county so there may be other applications including transmitter outside my search criteria.

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