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Old 14-12-2017, 09:25   #1
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Open source implementation of PACTOR-3 and -4

The newer PACTOR modems are notoriously expensive. At present, there is no competing, compatible product, let alone an open source one.

I'm thinking of changing that. I'm trying to gauge interest, because it's going to be a big job, and at some point (not until after I have tangible progress to show) I'm going to want financial support from the cruising community to do it.

I was employed by Motorola in the late 1990s where I was worked on WiMAX and various proprietary predecessor systems. I had previously worked for a company that manufactured modems and software for use on trunked radio systems in the 800 and 900 MHz bands. I have spent approximately 10 years full-time working with these systems, in engineering, engineering management, and field support roles. I have held an amateur radio license for approximately 20 years, although I have never been an active part of the amateur radio community.

With present-day computers, at the data rates that PACTOR achieves, it should be possible to implement the protocol entirely in software using an ordinary sound card for the audio interface.

But it's going to be a lot of work. I've reviewed the "protocol specification" for PACTOR-3 from the ITU. It's vague. The only thing I've found for PACTOR-4 is a one page description on the SCS web site. It will take some investigation to figure out what the existing products are actually doing, in detail. The basics are the same as every other RF modem in the marketplace -- though complicated, the methods are well understood.

Worth pursuing, or shall I keep repairing wooden boats in my spare time?
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Old 14-12-2017, 09:48   #2
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Re: Open source implementation of PACTOR-3 and -4

I would love to see this done, just for the nerdy technical aspect of it...

HOWEVER.. I think real interest will be quite low and falling each year. From my observation the last 2 years SSB use has been falling off. Sure we know quite a few cruiser boats equipped with SSB (and Pactor Modems), but they seem to be using them less and less. We keep hearing over and over "Yes, we have an SSB on board but haven't turned it on in 2 years". They have been replacing that use with SPOT, InReach or GO devices. Even more so now that both InReach and Go offer pretty good weather updates.

Maybe I will be proved wrong!
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Old 14-12-2017, 10:10   #3
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Re: Open source implementation of PACTOR-3 and -4

If I were to do it, I would start by contacting the development group of FLdigi. It would be a great base to work from and there is serious technical expertise there.

https://en.wikipedia.org/wiki/Fldigi
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Old 14-12-2017, 12:36   #4
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Re: Open source implementation of PACTOR-3 and -4

You might already be familiar with the amateur radio WINMOR, which achieves roughly PACTOR-2 speeds in software. There is also an upcoming improved, faster, protocol ARDOP, which should eventually replace WINMOR.

https://www.winlink.org/tags/winmor
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Old 14-12-2017, 12:50   #5
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Re: Open source implementation of PACTOR-3 and -4

Paul hit the nail on the head. Winmor is already a sound-card implementation of the PACTOR protocol. As an open-source project, they are always looking for volunteers willing to help them out with improvements and newer versions.
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Old 14-12-2017, 13:11   #6
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Re: Open source implementation of PACTOR-3 and -4

Jammer,

Are you thinking of reverse engineering the Pactor 3 & 4 protocols to create an SDR that can communicate with other Pactor 3 & 4 devices? Or, do you want to create a protocol and associated system that can achieve similar performance at a reasonable cost?



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Old 14-12-2017, 14:43   #7
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Re: Open source implementation of PACTOR-3 and -4

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Originally Posted by edguy3 View Post
Jammer,

Are you thinking of reverse engineering the Pactor 3 & 4 protocols to create an SDR that can communicate with other Pactor 3 & 4 devices? Or, do you want to create a protocol and associated system that can achieve similar performance at a reasonable cost?



/ed (w2VON)
The former.

In theory, the protocol details must be published for these protocols to be permitted for use in the USA in the amateur bands. A first step would be to identify whatever has been published. It might be necessary to encourage the manufacturer of the existing devices to publish a more complete protocol specification. Some reverse engineering may still be necessary.

Since there are open source versions of earlier PACTOR protocols, all that's really necessary is to add the higher modulation levels and the logic to shift gears. It's pretty routine stuff now since CPU capabilities are so much greater relative to the data rate over HF.
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Old 14-12-2017, 14:50   #8
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Re: Open source implementation of PACTOR-3 and -4

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Originally Posted by denverd0n View Post
Paul hit the nail on the head. Winmor is already a sound-card implementation of the PACTOR protocol. As an open-source project, they are always looking for volunteers willing to help them out with improvements and newer versions.
I'll take a closer look at what they're doing. I had thought their main focus was on a replacement protocol (ARDOP), and that they are still on the "extra hardware" path in requiring a TNC or a DSP card or maybe both.
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Old 14-12-2017, 16:33   #9
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Re: Open source implementation of PACTOR-3 and -4

Even a clean room open source implementation will most likely violate the Pactor held patents.
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Old 14-12-2017, 17:06   #10
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Re: Open source implementation of PACTOR-3 and -4

A related discussion is here:
Re: soundcard modems for pactorIII
I couldn't find the patents.
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Old 14-12-2017, 19:03   #11
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Re: Open source implementation of PACTOR-3 and -4

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Originally Posted by Jammer View Post
I'll take a closer look at what they're doing. I had thought their main focus was on a replacement protocol (ARDOP), and that they are still on the "extra hardware" path in requiring a TNC or a DSP card or maybe both.
All I know about it is from the website link and the 2015 overview document, but they mention both a software "virtual TNC" (Windows, Linux, Apple, Android) as well as a hardware implementation. Don't know how far they have taken it yet.
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Old 14-12-2017, 21:34   #12
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Re: Open source implementation of PACTOR-3 and -4

I am really hoping ARDOP comes to something eventually. I've been trying to follow the email mailing list but most of it is way over my head. I would love to see something open source but still fairly turnkey for non-technical folks that would run fairly easily on an older computer with a sound card and a simple connection to an HF radio. Hopefully the Linux version is simple to setup and implement, and is supported in Ubuntu for us dummies too.

One can wish upon a star, right?
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Old 15-12-2017, 04:16   #13
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Re: Open source implementation of PACTOR-3 and -4

If you can devote time to this project, ARDOP is the good way to get involved. My (limited) understanding is that Winmor is close to as good as it gets using a soundcard alone. For faster and more robust transmissions you need a hardware modem that has a better response rate.

Now, given SSB is declining in popularity, the sunspot cycle and the potential high cost of additional hardware - I would probably not commit much time. I think working on radar plugins for Open CPN is better value for me.
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Old 15-12-2017, 08:53   #14
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Re: Open source implementation of PACTOR-3 and -4

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Even a clean room open source implementation will most likely violate the Pactor held patents.
I would be very surprised if there are any enforceable patents that would complicate an implementation, let alone preclude it.

The thing to realize is that packet radio is not new. These technologies were commercialized over 30 years ago and in various forms are the basis of every cellular phone and base station, and every cable modem, since about 1990. There is nothing special about Pactor. It is simply these same techniques applied to HF.
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Old 15-12-2017, 10:58   #15
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Re: Open source implementation of PACTOR-3 and -4

So what are the key factors? I can think of:

* Modulation (M-ary, using PSK and ASK, and perhaps multicarrier)
* Forward Error Correction (lots of types here)
* Interleaving (optimized for the typical channel impairments of HF radio, FEC has to be tuned to work well with this)
* Medium-level protocol (mod/speed negotiation, real-time adjustments, uncorrectable error recovery method)
* Higher level protocol (ACK times and error rates can really screw this up, probably need spoofing of some sort to let the standard networking protocols work on top of all this.)

Anything else? The characteristics of the channel (HF radio in this case) deeply affect the implementation.
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