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TDMA vs FDMA range charcteristics

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2wayguy

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Has anyone done any real world testing on talk range capabilities between these two technologies? I have read in several places that TDMA has a more limited range due to time slots timing falling out of sync once you reach a certain distance from the transmitter. Any information would be greatly appreciated. Thanks
 

radioman2001

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Other than the manufacturers supposed testing, I don't think there is anyone who has done independent lab style testing of either format ala UL. I know in our case we were not impressed with the results of TDMA. FDMA is still being tested by our radio shops, and has shown promise. I still don't believe an 8db increase in range over analog which some are purporting.
 

2wayguy

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Thanks for the reply Radioman. Maybe someone will have done some real world testing and will respond to this thread.
 

nd5y

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I have read in several places that TDMA has a more limited range due to time slots timing falling out of sync once you reach a certain distance from the transmitter. Any information would be greatly appreciated. Thanks
That is true. Back when I worked for a cellular equipment manufacturer I remember some of the training material mentioned that TDMA-136 and GSM had a maximum cell site radius due to time slot collisions when one subscriber unit was right next to a cell site and another was far away. If I remember right GSM can also make the subscriber units vary the time slots slightly to compensate. I think the range was something like 120 km for TDMA-136 and 35 km for GSM. I don't know if any of this is applicable to DMR or P25. If I can find any information I will post it here.
 
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mikewazowski

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35kms is normal GSM range and extended range is 70kms although you cut your capacity in half.

I'm sure there is a range limit on p25 phase II and DMR but that would depend on the bandwidth.

Since both are only two timeslots, the range should be a lot higher.
 

SCPD

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The time slots are wider than the data - allows subscribers units to be early or late without stepping on one another. I don't think the slots are a limiting factor.
 

mikewazowski

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At some distance, the incoming signal will be delayed enough to step into the adjacent timeslot.

Whether this distance is within the operational range of the repeater is not known.

There is room within the GSM timeslot for 35kms of distance. I don't know if anybody has calculated the maximum distance for p25 or DMR based on the timeslot size and the size of the packet.

Since it's never been stated, we can probably assume that the room within the timeslot is sufficient to allow use out to the maximum range of the repeater.
 

SCPD

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We had Icom Idas up for 6 months or so, on 7 sites linked together. We then converted to Mototrbo, and finally came to Hytera DMR. The Hytera DMR gets us better range than the IDAS did. One issue we saw with Moto, was that when 2 portables were close together (10feet apart, and 12 miles from repeater) they desensed bad. With 2 Hytera portables in exact same locations, we saw no desense. Better filtering or forward error correction????
 

JRayfield

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I think that, in most cases, you're probably correct with regards to the maximum range of a repeater being more than the 'theoretical' maximum range of DMR. Consistently, when MOTOTRBO systems are designed properly, they have had more range than wideband analog, and of course narrowband analog, too, with all other factors being equal (same antenna systems, power levels, etc.).

When I hear of someone having less range with DMR (MOTOTRBO) than with analog FM (wide or narrow), I think there's something 'odd' going on with the system - either a problem in the design of the system, a problem with the equipment, or possibly some kind of interference that is more noticeable with a TDMA digital signal than with an analog signal.

As to TDMA vs. FDMA, with respect to range, that's a bit like comparing apples to oranges. The way forward error correction is handled, the type of modulation used, as well as specifics of the receiver and transmitter design, are going to have a large bearing on how they compare with each other in terms of range. So other than just comparing two specific brands/models of radios/systems, it's going to be hard to get a 'real world' comparison of the two and be 'fair' to both.

With everything equal, though, that is an interesting thought, if considered from a 'theoretical' standpoint.. I'll have to bounce this off of an RF engineer that I know and see what he thinks. His speciality is in RF propagation analysis and modeling.

John Rayfield, Jr. CETma

At some distance, the incoming signal will be delayed enough to step into the adjacent timeslot.

Whether this distance is within the operational range of the repeater is not known.

There is room within the GSM timeslot for 35kms of distance. I don't know if anybody has calculated the maximum distance for p25 or DMR based on the timeslot size and the size of the packet.

Since it's never been stated, we can probably assume that the room within the timeslot is sufficient to allow use out to the maximum range of the repeater.
 

SP4SKN

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digital modulation

Hello
I tested the Idas system and Nexedge. Idas has a smaller coverage than analog mode, but Nexedge has better coverage than analog ( in 6,25 KHz spacing of course). Kenwood radios has better coverage in analog mode than Icom radios. Tetra has a problem mentioned by ND5Y, also is more sensitive to the doopler effect. If you want good coverage and clean audio Nexedge is for you, but if you want good data transmision and dispatcher features - Tetra is better.

VY 73!
Stefan
 

AA9VI

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We had Icom Idas up for 6 months or so, on 7 sites linked together. We then converted to Mototrbo, and finally came to Hytera DMR. The Hytera DMR gets us better range than the IDAS did. One issue we saw with Moto, was that when 2 portables were close together (10feet apart, and 12 miles from repeater) they desensed bad. With 2 Hytera portables in exact same locations, we saw no desense. Better filtering or forward error correction????
We saw the complete opposite between MOT and HYT when we tested it in the Fall of 2012. Interesting.. what version of firmware was on each? You should use MOT firmware newer than R01.08.00.
 
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