On Apr 5, 2010, at 7:01 PM, vr2 xvd wrote: > hi all, > > > May I ask the follow question. > For a single site Voice communication digital repeater operation in identical > conditions, which format /system type will work better in multi path signal > ,with lager coverage area. > FDMA,TDMA (D-Star ,Mototrbo,P25,Nexedge,Idas) ? > > TNX & 73s > de VR2XVD/W.L.Ho
You will be spending a lot of time field testing to find out. There's no standard tests available for anything further than signal strength. It's rare to find necessary engineering data like at which Bit-Error Rate the CODECs fall apart, etc... to do proper engineering testing. GENERALLY: Multi-path: Digital falls apart sooner in multi-path conditions than analog does. Or should I say, before the DSP filter between your ears can't copy the analog signal. Larger coverage area: Has absolutely nothing to do with the protocol chosen, unless one were to prove that one or the other has a higher tolerance for BER. At the end of the day, nothing has rescinded the underlying physical RF principals, so a good antenna system, filtering, and pre-amplification if appropriate for the radio and the site -- will yield good results on all. All things being equal -- which they never are in the real world -- the protocol doesn't matter other than knowing at what BER the engineer chose to cut off the decoding and "give up". So... there's no one or right answer to your question. All you'll get is anecdotes in response. Which are useful for the 10,000' overhead "view" of what's going on out there, but not nearly as useful as lab testing. Individual systems (like P25, because of its widespread adoption in professional circles, and D-STAR because a VERY limited few hams have set up excruciatingly tedious and painstaking tests to try to reverse-engineer some of these answers - THANKS Utah VHF FM group, by the way, from ALL of us!) will have some test data published, often in obscure places, but I know of no one lab that has tested all of these together, same workbench, same standards. It will also be VERY hard to get a field-test answer to this question unless you had all of the repeater types (so you could alternately plug one or the others into the EXACT same antenna/pre-amp/filtering system, and had calibrated all of the mobile rigs to EXACTLY the same power output and ran them around in the exact same car, on the exact same antenna... then drive all over the coverage area and come up with some objective way of measuring "how does it sound". (In the wireline VoIP world, this would be done with the MOS score, for example. I've seen a FEW 2-way radio articles about how the CODEC was picked for P25 was done similarly, but there was no RF component involved in that system many years ago... just the choice of CODEC for intelligibility. Now they're starting to usE AMBE2, so obviously that tells us that, AMBE wasn't perfect...) If the engineering for the data side of things were available, better "guesses" could be made, with lots of assumptions... but good luck getting that data from the manufacturers. And you won't find any test gear capable of measuring all of the above systems that a) can do them all... but that will change... and b) doesn't cost more than a brand new foreign sports car. You've asked the question of a lifetime. Not because it's difficult, because it'll probably take about a lifetime for this all to shake out and someone to have the answer you're looking for. Your mileage may vary, -- Nate Duehr, WY0X n...@natetech.com
