Cruisers Forum
 


Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 15-12-2017, 10:56   #16
Moderator Emeritus
 
Paul Elliott's Avatar

Cruisers Forum Supporter

Join Date: Sep 2006
Posts: 4,663
Images: 4
Re: Open source implementation of PACTOR-3 and -4

Quote:
Originally Posted by Paul Elliott View Post
Anything else?.
Some Turbo-code FEC implementations are patented in the U.S. I don't know how well the patents prevent any other reasonable implementation.
__________________
Paul Elliott, S/V VALIS - Pacific Seacraft 44 #16 - Friday Harbor, WA
www.sailvalis.com
Paul Elliott is offline   Reply With Quote
Old 15-12-2017, 12:46   #17
Registered User

Join Date: Sep 2013
Location: Montreal
Boat: Dufour 39 Frers
Posts: 402
Re: Open source implementation of PACTOR-3 and -4

I am among those one that did not turned on the HF radio over the last 2 years!
But, this could be a reason to go back.
Emouchet is offline   Reply With Quote
Old 15-12-2017, 12:52   #18
Moderator
 
Jammer's Avatar

Join Date: Jan 2010
Location: Minnesota
Boat: Tartan 3800
Posts: 4,791
Re: Open source implementation of PACTOR-3 and -4

Quote:
Originally Posted by Paul Elliott View Post
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)
Yup, all part of it. I would add selective ARQ although I suppose that could be a form of "uncorrectable error recovery method" even though every RF based system I've seen uses selective ARQ in some form.

Add collision detection and recovery to your list.

I would also add radio control, which includes things like channel selection, identification of an open vs. busy channel, and various settling delays. More advanced systems have power management (ability to reduce transmit power when channel conditions are good to reduce cochannel interference to distant stations), although I don't believe PACTOR does.

Quote:
* 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.)
That's not done in the TNC. It is done in software layers above the TNC. Reviewing the literature, there certainly seems to be room for improvement in this area, but it's a separate project.

Quote:
Anything else? The characteristics of the channel (HF radio in this case) deeply affect the implementation.
HF is a walk in the park. Compared to UHF and up, which is where most commercial systems operate, HF has these properties:
- Relatively narrower available bandwidth in each channel.
- Very slow turn-around times between rx and tx, in some cases involving mechanical relays. (Cable modems have typical slot widths around a millisecond with tx to rx delays being a fraction of that)
- Propagation delay typically not a factor due to slow speeds even though distances are larger.
- Multipath interference perhaps less of a problem.
- Doppler effect not a factor due to lower frequency. At 2.5 GHz software has to compensate for people turning their head in the middle of a cell phone conversation
- There are sequential point-to-point sessions lasting seconds or more rather than time division multiplexing.

Unlike over-the-air systems in higher bands there's no dynamic bandwidth adjustment or diversity receive to contend with.
Jammer is offline   Reply With Quote
Old 15-12-2017, 13:21   #19
Moderator Emeritus
 
Paul Elliott's Avatar

Cruisers Forum Supporter

Join Date: Sep 2006
Posts: 4,663
Images: 4
Re: Open source implementation of PACTOR-3 and -4

I suspect that the channel impairments for HF are at least as tough to deal with as are VHF impairments. We have deep fading with stationary endpoints, short and long-duration static crashes (lightning) that are far stronger than the signal being received, higher levels of general atmospheric noise, and even multipath (although long-path / short-path multipath is much less common than VHF multipath, the duration is many symbols long.) QRM is more likely, especially in the ham bands.

Making something work isn't going to be too hard, but making something that works well when the going gets tough may not be so easy.

But I'm not going to try my hand at implementation -- there are some real experts out there already hard at it. I'm just happy to play with the results. Example: I'm using my RPi and Icom IC-7300 to run FT8 (see https://physics.princeton.edu/pulsar/k1jt/wsjtx.html.) The main guy on that -- Joe Taylor -- has a Nobel Prize in physics!)

By the way, what working familiarity I have with all this comes from my days in the telecom industry, designing (among other things) DSL and ADSL equipment.
__________________
Paul Elliott, S/V VALIS - Pacific Seacraft 44 #16 - Friday Harbor, WA
www.sailvalis.com
Paul Elliott is offline   Reply With Quote
Old 15-12-2017, 13:25   #20
Registered User

Join Date: May 2016
Posts: 84
Re: Open source implementation of PACTOR-3 and -4

I would like to see a software implementation referrred to.
Pactor 3, or 4. Pactor modems seem to be VERY expensive, and contrary to pricing in most areas of electronics.
As others said, efforts might be better used to support the open source software already underway.
Redpcx is offline   Reply With Quote
Old 15-12-2017, 13:55   #21
Moderator
 
Jammer's Avatar

Join Date: Jan 2010
Location: Minnesota
Boat: Tartan 3800
Posts: 4,791
Re: Open source implementation of PACTOR-3 and -4

I don't believe any projects that are actually open source have been mentioned upthread. While many are freely available in binary form from their sponsors, source is closed.

There are a few open source projects I've found that I'll investigate further.
Jammer is offline   Reply With Quote
Old 15-12-2017, 13:59   #22
Moderator Emeritus
 
Paul Elliott's Avatar

Cruisers Forum Supporter

Join Date: Sep 2006
Posts: 4,663
Images: 4
Re: Open source implementation of PACTOR-3 and -4

Check out the source code for Joe Taylor's projects (https://physics.princeton.edu/pulsar/k1jt/devel.html). Joe and his friends know something about HF data comms!

It's interesting that "most of the number crunching" is done in Fortran. Well, Joe is even older than me, so I guess that makes sense. Converting Fortran shouldn't be that hard. I don't know Fortran, but at various times I've successfully converted some over to C or C# or VisualBasic.
__________________
Paul Elliott, S/V VALIS - Pacific Seacraft 44 #16 - Friday Harbor, WA
www.sailvalis.com
Paul Elliott is offline   Reply With Quote
Old 15-12-2017, 19:19   #23
Registered User
 
hzcruiser's Avatar

Join Date: Aug 2008
Location: Sydney, Australia
Boat: Roberts 45
Posts: 1,034
Re: Open source implementation of PACTOR-3 and -4

That's some very good feedback you got in this thread, Jammer.

The demand and hence the market is shrinking with the sat comm prices coming down every year.

You'd still need an expensive full-fledged HF radio on the back end plus some sophisticated modem hardware, most likely DSP based, to squeeze more data through the very narrow HF band. SCS has been doing this for decades and I assume they have a dedicated R&D team working on the improvements of their proprietary modulation algorithm. That would be hard to beat with a group of freelancers starting from scratch. Their modems are crazy expensive, yes, but they also don't sell them by the tens of thousands, yet have to run their business in the profit zone.

If you really aim to reverse-engineer their algos I'd expect them to throw some serious legal punches your way.

Don't get me wrong, I'd also love to have more (and affordable) bandwidth and reliability on HF, whether on the marine bands or ham! Apart from sat, LF/MF and HF are still the only alternatives we have for long distant comms out on the ocean.

Good luck to you and keep us posted, please!

As mentioned before, fldigi would be something I recommend looking into and it's what I'm using ATM, but I also have an upgraded Pactor PTC-IIe sitting here. Still need to find the time to hook it up again and get back on the air...
__________________
Fair winds,
heinz

https://www.timantra.net
hzcruiser is offline   Reply With Quote
Old 16-12-2017, 03:20   #24
Registered User
 
svMarite's Avatar

Join Date: Jul 2012
Location: New Bern, NC
Boat: Shannon 43 Ketch
Posts: 246
Re: Open source implementation of PACTOR-3 and -4

I'm fascinated by this thread - you guys are WAY over my head, as I've been away from this for years. I'm installing an Icom aboard for voice and wx fax primarily, with a digital Sat capability for limited email as the Iridium and others come more online. I don't believe the voice/data/VOIP will be available to mariners for some time at a reasonable cost that is.
I have to ask to what end is the goal - email, text over Virtual Radio? I would venture to suggest the military has spent millions in contracted solutions using a hybrid of HD, VHF and cellular technologies to cover a battlefield back boned by a robust but finite Sat system.
My point is as mentioned previously - would it be worth the effort? Am I interested as a consumer? Certainly - as stated, Pactor has the market cornered. Our market segment is particularly small though, thus to what end?
I hope you guys don't mind me following along as you proceed with this line of discussion.
BTW - my background is retired Special Forces communications and SIGINT collector. I sailed twice across the pond and on that return leg, I had an SSB aboard to listen to Southbound II to get weather, as well as download NMF. I'm into KISS as we have enough to do on our voyaging vessels anyway.
I would venture to guess that as Sat Bandwidth diminishes due to volume of requirements, I could see SF teams wanting to revert to this simpler mode of comms, as they're still using HF. If you found a simple Open Source method to create a virtual pactor - I'd bet they'd be very interested in it.
__________________
Smooth sailing and fresh warm breezes,
Tony & Lisa
sv Marite
'87 Shannon 43' Ketch
svMarite is offline   Reply With Quote
Old 16-12-2017, 05:25   #25
Moderator
 
Jammer's Avatar

Join Date: Jan 2010
Location: Minnesota
Boat: Tartan 3800
Posts: 4,791
Re: Open source implementation of PACTOR-3 and -4

Quote:
Originally Posted by Paul Elliott View Post
Check out the source code for Joe Taylor's projects (https://physics.princeton.edu/pulsar/k1jt/devel.html). Joe and his friends know something about HF data comms!
Thanks, I'll take a look.

Quote:
It's interesting that "most of the number crunching" is done in Fortran. Well, Joe is even older than me, so I guess that makes sense. Converting Fortran shouldn't be that hard. I don't know Fortran, but at various times I've successfully converted some over to C or C# or VisualBasic.
There are compilers available. GNU Fortran uses the same code generator as GCC, and is open source. But, as you point out, it isn't hard to convert the code by hand. I studied Fortran when I was in high school but have never used it professionally.

Quote:
Originally Posted by hzcruiser View Post
That's some very good feedback you got in this thread, Jammer.

The demand and hence the market is shrinking with the sat comm prices coming down every year.
I do appreciate the feedback, and the emerging consensus that HF data technology may not remain relevant is the largest barrier to pursuing this.

Quote:
You'd still need an expensive full-fledged HF radio on the back end plus some sophisticated modem hardware, most likely DSP based, to squeeze more data through the very narrow HF band.
HF radio, yes, sophisticated modem, no. The encoding for TX is easy and can be done completely in software at these speeds even with older computers. The decoding is more difficult, but I believe that with today's computers, in the very narrow HF data band, there is enough CPU capacity to run an adequate demodulator in software without a DSP or some custom or semicustom chip.

Quote:
SCS has been doing this for decades and I assume they have a dedicated R&D team working on the improvements of their proprietary modulation algorithm. That would be hard to beat with a group of freelancers starting from scratch. Their modems are crazy expensive, yes, but they also don't sell them by the tens of thousands, yet have to run their business in the profit zone.
If they are like other companies, such R&D resources as they still have on board are probably working on cost reductions and maintaining compatibility with new releases of Windows.

I don't want to compete with them. I don't want to beat them. I just want to further the public interest by making a software-only solution (using inexpensive off the shelf interface components, like sound adapters) available on an open source basis.

Quote:
If you really aim to reverse-engineer their algos I'd expect them to throw some serious legal punches your way.
This is one of the themes here and I do want to make a few things clear. I'm in the USA. I'm not going to do anything that I believe is a violation of US law or that I believe is an infringement of copyright or patents that are valid in the USA. Not only that, I'm not going to do anything that would require users of the software I write to do something I believe is unlawful. I'm not going to steal anything. The premise of this project is that everything is going to be above board.

I've been on the other side of this and have been in countless classes, presentations, and meetings to try to come up with patent strategies to make life hard for my previous employers' competitors. I've read patents, reviewed prior art, proposed patents, met with patent attorneys, yada yada yada. And the bottom line is that it is extremely difficult to get a valid, enforceable patent covering wireless communications. Even then, they're only valid for 20 years.

Quote:

Don't get me wrong, I'd also love to have more (and affordable) bandwidth and reliability on HF, whether on the marine bands or ham! Apart from sat, LF/MF and HF are still the only alternatives we have for long distant comms out on the ocean.

Good luck to you and keep us posted, please!

As mentioned before, fldigi would be something I recommend looking into and it's what I'm using ATM, but I also have an upgraded Pactor PTC-IIe sitting here. Still need to find the time to hook it up again and get back on the air...
Thanks for that, and I will.
Jammer is offline   Reply With Quote
Old 16-12-2017, 07:08   #26
Registered User

Join Date: Dec 2009
Location: New York Harbor
Boat: Hunter 40.5
Posts: 26
Re: Open source implementation of PACTOR-3 and -4

Quote:
Originally Posted by Jammer View Post
And the bottom line is that it is extremely difficult to get a valid, enforceable patent covering wireless communications.
Indeed, but the etchings look so nice on the wall!
__________________
_/)_ S/V SeaGazer
edguy3 is offline   Reply With Quote
Old 23-02-2018, 08:05   #27
Registered User
 
flyingnut40's Avatar

Join Date: Jan 2014
Location: Bas Caraquet, New Brunswick, Canada
Boat: VDS Seal 36 and Sandpiper 565
Posts: 346
Re: Open source implementation of PACTOR-3 and -4

Following
__________________
Live your life with passion, even if it kills you, because something is going to kill you anyways. Webb Chilies
flyingnut40 is offline   Reply With Quote
Old 23-02-2018, 08:45   #28
Moderator Emeritus
 
Paul Elliott's Avatar

Cruisers Forum Supporter

Join Date: Sep 2006
Posts: 4,663
Images: 4
Re: Open source implementation of PACTOR-3 and -4

Quote:
Originally Posted by edguy3 View Post
Indeed, but the etchings look so nice on the wall!
Now I am forced to show you my Ego Wall:


Unfortunately there's nothing there related to demodulation or FEC. There is a fair amount of DSP though, just not in that domain.
__________________
Paul Elliott, S/V VALIS - Pacific Seacraft 44 #16 - Friday Harbor, WA
www.sailvalis.com
Paul Elliott is offline   Reply With Quote
Old 21-01-2019, 17:51   #29
Registered User
 
akopac's Avatar

Join Date: Oct 2014
Location: South Pacific -> World Cruising Long Term
Boat: Morgan, West Indies 38 Ketch
Posts: 555
Re: Open source implementation of PACTOR-3 and -4

My 2 cents,...

In keeping with low power open source, low cost I would start with what already is being worked on ARDOP, PAT, and a Raspberry Pi. Why a Raspberry Pi?
1. It is is extremely low power
2. It runs Opencpn/plotter w/tons of add-ons and compatible hardware including sound hardware
3. It already runs WL2K PAT and will work with a pactor modem or otherwise with ARDOP
4. You can use the Raspberry Pi as a wireless access point and go headless, VNC sharing the screen to any phone, tablet or laptop. Be aware new low power screens will be coming out for tablets. Search Clearink
5. It's so cheap you can afford to have plenty of backups

I could go on but it just makes too much sense. What is missing from open source PAT is:
1. Propagation Prediction interphassed with rig control
2. Saildocs catalog interphase
3. A clean full install package.

Speed of transmission of data is important, but making all this portable is important too. PAT runs on anything. It was programed in GO an easy language to work in.
akopac is offline   Reply With Quote
Old 21-01-2019, 19:26   #30
Moderator
 
Jammer's Avatar

Join Date: Jan 2010
Location: Minnesota
Boat: Tartan 3800
Posts: 4,791
Re: Open source implementation of PACTOR-3 and -4

Quote:
Originally Posted by akopac View Post
My 2 cents,...

In keeping with low power open source, low cost I would start with what already is being worked on ARDOP, PAT, and a Raspberry Pi. ...

I'll take a look at that stack. I have some work-related Raspberry Pi stuff to do anyway and it would be a good exercise.


I thought that the pis lacked any sort of bluetooth or WiFi radio unless one is added as a separate board. The ones I have in my lab only have the 100baseT port, USB, and the GPIO connector -- no wireless of any kind.


I do see the appeal of the pi but consider it a poor fit for actual use aboard. I like the Logic Supply computers -- better enclosure, more reliable SSD, dual HDMI outputs, built-in 12v power supply, better networking options including 1000baseT and wireless, better environmental specifications particularly heat tolerance.
Jammer is offline   Reply With Quote
Reply

Tags
men, pactor

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Navico BR24 Radar - Open Source protocol implementation maxxflow OpenCPN 23 30-07-2012 04:20
For Sale: Pactor 2 Pro with Pactor 3 license installed s/v Holiday Classifieds Archive 1 28-07-2012 22:24
New Waypoint Properties Implementation nohal OpenCPN 206 14-07-2012 12:38
For Sale: Icom 802, AT 140, Pactor 2 w Pactor 3 lic Vyndance Classifieds Archive 10 02-06-2012 17:38

Advertise Here


All times are GMT -7. The time now is 06:04.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.