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Digital Voice Mode on GMRS - Possible Rules?


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I was thinking here tonight about digital voice modes on GMRS. I’m sure it will happen sooner or later. What I haven’t seen is a good discussion on how it should be done. If there is any chance the FCC would be receptive to the idea then a good reasoned plan on the implementation I think would help push it along.

So what would be a reasonable plan be and what mode(s) make sense? I’m going to guess the one thing the FCC won’t do is expand the spectrum. They might would entertain splitting existing 25KHz channels into two 12.5KHz or four 6.25KHz ones.

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I'll bite! :) 

Well, since GMRS/FRS is meant to be "easy to use" I'd say replicate what the DTR radios on the 900mhz band are doing. Set a 16-bit or 20-bit pseudo random FHSS sequence and have them hop in the upper 12.5kHz of every wideband GMRS channel, and use the whole 12.5kHz for the FRS channels.

IMO. it doesn't get any simpler than that. Eiter 65k channels, or 1M channels, depending on 16 or 20 bit for the random FHSS sequence.

G.

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That’s not a bad idea.

I was thinking along the line of using the nearly useless narrow band channels 8 to 15.  Currently at 0.5 watts many GMRS radios don’t even include them. If the digital mode was restricted to  those channels at 2 to 5 watts and 6.25KHz bandwidth the interference to the adjacent wide band repeater channels would be minimal.

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Using 4FSK I think would be easier than a FHSS. A standard would have to be established so all radios could communicate with radios from other manufacturers. Then you need companies like Motorola to open up their proprietary design they use on their FHSS radios. I’m not confident they would entertain that idea.
 

With 4FSK at least two standards already exist, NXDN (primarily USA) and dPMR (primary European Union). Both are “true” 6.25KHz technologies. Either one would be suitable to use. More than one company manufacturers radios for each of the above already. Also the FCC has moved into splitting 12.5KHz channels into two 6.25KHz.

I would vote for NXDN since it widely used in the US already in various sectors. Used commercial radios are not terribly expensive either. In fact, for example, the NX-300’s in the 450-520 band split have FCC Part 95 certification already. They can do wide and narrow band FM along with narrow band digital (12.5 KHz) and very narrow band digital (6.25 KHz).

NXDN White Paper.pdf DA-12-10A1.pdf

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I think you are confusing 4FSK and FHSS. You can FHSS in any modulation, be it FM... SSB, etc. 

Anything narrowband will just run into the same service (22 channels) problems we are facing right now: interference and band congestion/saturation, and that includes NXDN too which is still narrowband BTW, and it doesn't matter how much narrowband it can get. At best, if all channels were to be split in 4 (or 2), you'll only get a few additional channels over the pre-existing 22, and that would be assuming the FCC ever makes 6.25kHz mandatory, which we both know it won't happen. So its a waste of time to provide the least efficient RF digital format there is. TDMA 2-slot offers double the spectral efficiency over a single 12.5kHz, and please, spare me the BS about you being able to split a channel in 2... hahaha, with what filters? 600kHz split in Ham repeaters already requires 6" cans the size of oxygen tanks.... Then, even if all channels were split in 6.25 chunks, that will only provide roughly 88 channels... at best... vs a 1 Million interference-free channel pool with a properly implemented 20-bit FHSS scheme.

In addition to that, FHSS also provides other benefits that NXDN simply can't and will never be able to afford: far superior spectral efficiency, slightly better range (due to frequency hopping, (if one particular frequency is blocked, the next hop frequency might not), very strong interference resistance, a good deal of privacy against casual eavesdropping, and all that without the use of the big no-no word called "encryption."

Using narrowband and analogue stuff is the way of the dinosaurs. DMR is also narrowband but its saving grace would be its using a TDMA (Time Division) scheme, and can do something that NXDN will never be able to do: Have 2 concurrent conversations over the same single 12.5kHz channel. I think its called 6.25kHz equivalency...

With that said, and for as much as I am invested in DMR, I would rather see the implementation of an open FHSS (ETSI/ANSI) standard instead.

G.

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My point, and goal, with this thread are possible rules that would allow digital voice to be used within the current confines of the spectrum currently allocated to GMRS operation. The chances of the FCC adding spectrum is nearly zero. 

The prior attached file shows the FCC has allowed splitting existing commercial channels into narrower allocations. The same could be done with GMRS all without adding additional spectrum. On the other hand there would be a gain of some extra simplex channels. The practicality of close by stations operating on adjacent 6.25KHz channels is another point. Of course if the stations are geographically separated it likely won’t be an issue.

While DMR has some good points it does require coordination between radios utilizing the same frequency to take advantage of DCDM. The occupied bandwidth is still 12.5KHz regardless if one or two slots are used. The 6.25KHz is only an “equivalent” due to the dual slot nature of the transmissions. Trying to squeeze a DMR signal in between let’s say the main repeater channels is exactly the same as the current low power, and basically useless, FM 12.5KHz ones. I was thinking that a true very narrow band digital signal might be used there while resulting in even less interference and and maybe at a higher power for simplex operation.

At the moment both NXDN and dPMR are both established digital protocols. There is no necessity to try and standardize a FHSS CAI. This is a necessity if there are going to be multiple manufacturers of these FHSS types of radios. And of course they will have to communicate among themselves too. Utilizing one of the above, NXDN dPMR, is a known standard with lots of field experience and one less item for the FCC to use as an excuse to claim it isn’t proven or accepted by the market place or can’t coexist with current FM technology.

 Now about DMR, I like it. Yes it can be used however I don’t see how without dedicating specific channels to it. That of course would tick off the FM only users. So the big question is where do you put it or just make it the Wild West and let the users fight it out. The other advantages are the reduced average power, great for hand held radios, and the single frequency repeater operations. Given the number of times you see people asking about setting up their own repeater this would make it almost brain dead simple to do, and no special equipment like tuned cavity filters to deal with.

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How are you arriving to this conclusion about needing more bandwidth?

A 12.5kHz channel FHSS scheme over whatever GMRS bandwidth already has currently allocated won't require any additional spectrum to be allocated. So I am not sure what is it you are talking about.

Next point: this is not a NXDN vs DMR as you'd like it to be.... and then to reiterate this AGAIN, b/c you seem to just ignore the fact that I am NOT endorsing DMR as a potential GMRS digital modulation, so please pay attention to what I am saying before lecturing me about how super-duper NXDN is, well let me tell you: that is your opinion, and you are entitled to that. I don't agree with it, and I find NXDN totally useless and lacking for many reasons, and certainly for the purpose of de-congesting the GMRS allocated bandwidth.

So, I'll state this once again: FHSS, (or DSSS), is the best way to go in so many ways: avoids pissing other users off with random lids barge into your conversation, or hijacking repeaters... etc, and you get 1 MILLION channels, that is: 1,000,000 channels.... no amount of NXDN voodoo BS is going to compete with that.

Maybe you don't understand what FHSS really is?

Again, you just can't beat that kind of spectral efficiency of an FHSS scheme with anything single-channel narrowband like DMR/NXDN/TETRA/P25/<insert your single channel narrowband modulation name here>. The RC world has been doing this for almost 2 decades now, where you can have dozens of models flying simultaneously next to each other without interfering each other... well, don't try that with any single-channel narrowband stuff...

G.

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Yes I have a basic understanding of the concepts. I have some material on it in my personal library. The first photo is a section out of one of my books on digital satellite communications. It’s also allowed in amateur radio by the way. That’s the second photo.

F1962A22-59A8-4A07-8C98-EC0C57A36C8A.jpeg

9A6A2CC5-C5FD-4D50-B9C2-5DE4DC87C68D.jpeg

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Not sure what to say, but a couple of pictures of a book doesn't show me understanding of the concept, but that's fine.

In a nutshell: FHSS is a Frequency Hopping Scheme, or Frequency Hopping Spread Spectrum: which could be considered a combination of FDMA (Frequency Division, Multiple Access) and TDMA (Time Division, Multiple Access) in one package. Transmits for a few milliseconds on a given frequency, then it hops to another frequency and transmits again, rinse and repeat. Whatever frequency the radio will hop to next is determined by a random seed number, and a counter. So when both radios hop in the same pattern then you have a viable radio link, but when they do not, the two radios can't talk to each other, nor have a clue that another radio is even talking.

At any rate, my vote goes for FHSS, just like the DTR radios in the 900 Mhz band have already proven it works very well.

Again, I am also NOT endorsing Motorola radios either, just making a reference to their FHSS scheme.

Also, military grade radios use FHSS as well, for all (but not limited to) the reasons I've explained.

G.

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So the point here is how would you present this to the FCC as a proposed rule change(s)?

The FCC will likely take the path of the least resistance. That means if more of the work can be done by us ahead of time, anticipate possible objections etc. then have reasonable solid answers the more likely it will get serious consideration. In other words we have to do their job for them.

Don’t forget there will be others out there who likely DON’T want to see any changes. There is always that crowd and that has to be taken into consideration too.

Then you have the manufacturers that will likely chime in if they feel a competitor may gain an advantage depending on what selection is made, if any. Who knows the FCC could be persuaded to allow multiple digital voice modes. 

Based on how this is turning out I’m of the current opinion it was a mistake to even bring up the idea. The debate isn’t over personal preferences. There is nothing to be gained or to facilitate the goal here by trying to prove who knows more except to derail the idea. If others want to continue, fine. But I’m done with.

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Well, I'd say however it was done to get the 2.4 GHz ISM band for WiFi, BT, BT Intercoms, etc... that is probably what needs to be done to the GMRS service as well.

The devices themselves (no user input) negotiate handshakes, packet collision, etc, and leave the user to just select whatever "channel" among a large pool of "channels", whether these channels being "physical" channels or "virtual" channels, and some privacy codes.. etc.

There is/was nothing personal about stating that FHSS is a better scheme for spectral efficiency than any narrowband single-channel modulation, including FM, NXDN, DMR, et. all.

An open standard will need to be implemented for this, be it an ETSI standard, or be it ANSI standard. whatever, It just cannot come from a single manufacturer, and that includes Motorola, Kenwood, et. all.

G.

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