Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 17-07-2018, 01:31   #1
Registered User

Join Date: Jul 2018
Posts: 4
VHF-transmission identification challenge

Hello guys, I am new to this forum so a quick introduction of myself to start with.

I'm Nicholas a 22 year old student from Belgium. Currently, I'm working on a research project revolving around VHF transmissions of seagoing commercial vessels. A while ago, I stumbled upon a challenge, however, which I would gladly like to explain to you in the hopes that one of you experts could help me out.

In order for the project to succeed, I would have to link a ship's identification (MMSI, name, anything to be able to identify it) to its VHF transmission when talking to the pilot station or coast guard for example. I have already tried a couple of things, but nothing successful yet.

The first thing I found was the so called ATIS-code that gets sent with European inland ships' VHF-transmission. But since I am focussing on seagoing vessels and they aren't obliged to use it, this method won't work.

Secondly, I tried working with triangulation, but because of the straight shape of the Belgian coastline, this proved to be very tricky and infeasible.

Next thing I tried was to use a list of 'expected vessels' and try to use text recognition to filter out the vessel name, but even this wasn't accurate enough because of the international accents of the captain and crew talking.

Basically that's where I'm at right now. Some sources told me that the MMSI-number gets sent along with every VHF-transmission, but nobody has been able to confirm this to me, nor how I would be able to filter this out.

Can any of you experts help me with this challenge or provide me with an (out of the box) solution or insight?

Looking forward to your takes on this issue!

Cheers
__________________

NicholasM is offline   Reply With Quote
Old 17-07-2018, 01:40   #2
Registered User

Join Date: Sep 2016
Posts: 20
Re: VHF-transmission identification challenge

Hi there, have you read this?
http://www.marinyachtclub.com/files/DSC%20MMSI.htm

When a radio operator uses the DSC function, DSC is what you get.
"DSC uses channel 70 to send the digital signal".
As far as I know, traditional use of VHF, eg. on channel 16, is just that, no digital transfer of any other data goes along with the analog voice communication. I'm no expert, don't take this as the absolute truth.
You could do some test calls and DSC button pushes while measuring any activity being sent from the VHF device... You need a radio operator license for that, in theory.


Be aware that it is more in practice today to look for a ship name on a chart plotter with AIS, voice communication is then initated on VHF 16 by calling the vessel by its name.
__________________

JeroenAdam is offline   Reply With Quote
Old 17-07-2018, 02:05   #3
Registered User
 
CatNewBee's Avatar

Join Date: Aug 2017
Boat: Lagoon 400S2
Posts: 965
Re: VHF-transmission identification challenge

DSC was invented to do this, but frankly no one really uses it perhaps except for automatic distress calls. Even coast stations viewing your AIS data on the screen are hailing you on 16 by voice only instead of using DSC. Its faster, more conveniant and not all vessel have a DSC capable transmitter too.

Many boats have the transmitter on the nav station inside and not at the helm, so a lot of routine calls are often ignored, especially shorthanded amateur crews often even do not turn on the VHF.

If you use voice only communication, no data is transmitted, only invoking DSC calls transmit your MMSI and vessel name, and additional data according to the type of call you chose (e.g. call type, distress reason, position data, bearing, SOG, time stamp, destination MMSI / GROUP / all ships etc.

There are a lot of flimpsy clicks in a two button UI until a call is invoked, so most simply use voice only.
CatNewBee is offline   Reply With Quote
Old 17-07-2018, 06:06   #4
Moderator
 
Paul Elliott's Avatar

Cruisers Forum Supporter

Join Date: Sep 2006
Posts: 4,370
Images: 4
Re: VHF-transmission identification challenge

Do you need to use voice VHF for this study? If you can, monitor AIS instead. AIS transmissions are at the top end of the marine VHF channel, and each of these digital transmissions contain the vessel MMSI number. These transmissions happen every few seconds or minutes, so you will have lots of data to work with.
__________________
Paul Elliott, S/V VALIS - Pacific Seacraft 44 #16 - Friday Harbor, WA
www.sailvalis.com
Paul Elliott is online now   Reply With Quote
Old 17-07-2018, 06:53   #5
Registered User
 
CatNewBee's Avatar

Join Date: Aug 2017
Boat: Lagoon 400S2
Posts: 965
Re: VHF-transmission identification challenge

Quote:
Originally Posted by Paul Elliott View Post
Do you need to use voice VHF for this study? If you can, monitor AIS instead. AIS transmissions are at the top end of the marine VHF channel, and each of these digital transmissions contain the vessel MMSI number. These transmissions happen every few seconds or minutes, so you will have lots of data to work with.
Can you explain this please, AFAIK, DSC and AIS use separate channels, not related to voice traffic. Basically he wants to know who is calling, this information is only available if DSC is used for the initiation of an conversation, the voice channels do not provide digital fingerprints (yet).

Therfore each party has to follow the protocoll and always preamble recepient and sender when talking, followed by over or out, because of simplex channels and everyone around is listening.

That is also the reason you need a SRC / operator license to use VHF.
CatNewBee is offline   Reply With Quote
Old 17-07-2018, 07:14   #6
Moderator
 
Paul Elliott's Avatar

Cruisers Forum Supporter

Join Date: Sep 2006
Posts: 4,370
Images: 4
Re: VHF-transmission identification challenge

Quote:
Originally Posted by CatNewBee View Post
Can you explain this please, AFAIK, DSC and AIS use separate channels, not related to voice traffic. Basically he wants to know who is calling, this information is only available if DSC is used for the initiation of an conversation, the voice channels do not provide digital fingerprints (yet).

Therfore each party has to follow the protocoll and always preamble recepient and sender when talking, followed by over or out, because of simplex channels and everyone around is listening.

That is also the reason you need a SRC / operator license to use VHF.
I suggested AIS because it was not clear to me if the OP actually needed the voice/DSC signal for this project. If this was a radio propagation study, for example, then AIS would serve quite well. If the project is to use speech recognition in order to study voice transmissions (for example) then AIS will obviously not be appropriate.
__________________
Paul Elliott, S/V VALIS - Pacific Seacraft 44 #16 - Friday Harbor, WA
www.sailvalis.com
Paul Elliott is online now   Reply With Quote
Old 17-07-2018, 07:37   #7
Registered User
 
ranger42c's Avatar

Join Date: Aug 2012
Location: Maryland, USA
Boat: 42' Sportfish
Posts: 3,356
Re: VHF-transmission identification challenge

DSC calls on Channel 70 to our VHF radio (using our MMSI) do nothing more than alert us to the hail, and then switches our radio to a suitable voice working channel. There's no further related signaling on Channel 70; subsequent conversation happens on the voice working channel.

I think I remember MMSI-enabled AIS signals are in the marine VHF band.

Maybe better suggestions depend on whether Nicholas is trying to track ships, or VHF radios... or something else.

-Chris
__________________
Selby Bay, South River, Chesapeake Bay, USA.
ranger42c is offline   Reply With Quote
Old 17-07-2018, 15:18   #8
֍֎֍֎֍֎֍֎֍֎

Cruisers Forum Supporter

Join Date: Apr 2006
Posts: 14,162
Re: VHF-transmission identification challenge

"In order for the project to succeed, I would have to link a ship's identification (MMSI, name, anything to be able to identify it) to its VHF transmission when talking to the pilot station or coast guard for example."

Then I would think the project cannot succeed, as there is no mandated link, identification, or association between any vessel ID and any VHF voice transmission, as far as I know.

If you are talking about commercial traffic only, then there are regulations about radio systems and use, but none for general traffic. And not all vessels comply with regulations.
hellosailor is offline   Reply With Quote
Old 18-07-2018, 00:40   #9
Registered User
 
CatNewBee's Avatar

Join Date: Aug 2017
Boat: Lagoon 400S2
Posts: 965
Re: VHF-transmission identification challenge

Quote:
Originally Posted by hellosailor View Post
"In order for the project to succeed, I would have to link a ship's identification (MMSI, name, anything to be able to identify it) to its VHF transmission when talking to the pilot station or coast guard for example."

Then I would think the project cannot succeed, as there is no mandated link, identification, or association between any vessel ID and any VHF voice transmission, as far as I know.

If you are talking about commercial traffic only, then there are regulations about radio systems and use, but none for general traffic. And not all vessels comply with regulations.
There are regulations all station user has to comply to.
It is a voice based protocol.

First you listen, if there is a conversation on 16.
If not there are various priority calls

distress, emergency, safety, routine.

there are buzzwords, like MAYDAY, PANPAN, SECURITE that indicate a priority call, they must be repeated 2 times before starting a conversation, routine calls have no buzzword.

Then you have to name the targed at least 2 times, it could be another vessel name, callsign, all ships etc, then you have to provide your station name at least twice, also spell it if necessary using the international alphabet (Alpha, Bravo, Charly, ...), your callsign, spelled, your MMSI number if applicable, then a short message what you are up to concluded by OVER, if you expect an answer or OUT, if you end the conversation.

Routine calls, safety calls usually are hailed on 16 by proposing a new working channel, and then the conversation takes place there. Once a conversation is started, every station has to begin a new answer / transmission with destination name, 'this is' your station name, followed by the message, followed by OVER or OUT. So everybody knows, when you finish talking and the channel is again free to be used.

Emergency calls remain on channel 16, so everybody knows what is going on. Emergency calls have also a proposed structure, starting with 3x mayday, station name 3 times, callsign spelled 2 times, position repeated 2 times, type of emergency (there is a catalog of internationally understood types), what type of assistance needed, how many people on board, insuries, type of emergency gear available, planned next steps e.g. abandon ship to life raft etc.

Every number has to be repeated, every name has to be repeated and spelled, so the ships around have a chance to write down a protocol of the reception and if necessary, to re-transmit your Mayday (if no SAR station answers in a timely manner), It is then a urgency MAYDAY RELAY call.

All other station have then to keep radio silence so SAR can communicate free to the vessel, until SAR releases the channel with SEOLANCE FINI.

There is a reason you need a radio station operator license to use marine VHF. It is an internationaly regulated communication protocol, that keeps all safe at sea.

If you want more details, check out online documentations, courses on RYA, SRC etc.
CatNewBee is offline   Reply With Quote
Old 18-07-2018, 02:03   #10
Registered User

Join Date: Apr 2007
Location: Australia
Boat: Island Packet 40
Posts: 1,805
Images: 7
Re: VHF-transmission identification challenge

Interesting problem.

If I understand your post correctly you are trying to reliably "attach" a relatively anonymous VHF transmission to an individual of one of a number of AIS data packets.

In practice there is considerable differences in the characteristics of VHF signals received. These appear to be dictated by the quality of the transmitter of the sending VHF. Assuming that the same VHF radio is being used for both AIS and voice transmission It might be possible to characteristic match the transmissions with a computer and signal analysis software.
RaymondR is offline   Reply With Quote
Old 18-07-2018, 02:11   #11
Registered User
 
CatNewBee's Avatar

Join Date: Aug 2017
Boat: Lagoon 400S2
Posts: 965
Re: VHF-transmission identification challenge

Quote:
Originally Posted by RaymondR View Post
Interesting problem.

If I understand your post correctly you are trying to reliably "attach" a relatively anonymous VHF transmission to an individual of one of a number of AIS data packets.

In practice there is considerable differences in the characteristics of VHF signals received. These appear to be dictated by the quality of the transmitter of the sending VHF. Assuming that the same VHF radio is being used for both AIS and voice transmission It might be possible to characteristic match the transmissions with a computer and signal analysis software.
its not reliable. AIS transmitter is a different device than a VHF radio, they (sometimes) may share an antenna, but there is also the usage of handheld radios very common at the helm, so both devices have nothing in common, signal strength, transmitter frequency and quality, antenna - all different. BTW AIS is a digital transmission, hard to compare to analogue voice with noise etc.

And also very few leasure vessel do have an AIS transmitter, that is on all the time - beside charter fleets.


The only way may be to do a fox hunt, using several directional antennas to locate a transmitter station. But the transmissions are too short to have enough time for triangulation. Next problem would be to reliably identify all vessel in a crowded area and tell which one of them was the transmitter. Imagine an anchorage, marina, harbor - no way you can extract one radio station by its signal only.

Also the range of reception may be between 1nm and 40nm depending on set signal strenght, antenna height and obstructions / noise from other transmissions. You must be in vincinity with your equipment to track it down, it is a moving target too.
CatNewBee is offline   Reply With Quote
Old 18-07-2018, 02:41   #12
Certifiable Refitter/Senior Wannbe
 
Wotname's Avatar

Cruisers Forum Supporter

Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: C.L.O.D.
Posts: 8,260
Re: VHF-transmission identification challenge

RF surveillance experts tell me that every transmitter has it's own unique "fingerprint" for a the first few milliseconds after it is keyed. This is just a product of the transmitter coming up to its carrier frequency.

You would need some seriously expensive spectrum analysers and recorders to make use of this apparent fact.
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
Wotname is offline   Reply With Quote
Old 18-07-2018, 03:05   #13
Registered User
 
ranger42c's Avatar

Join Date: Aug 2012
Location: Maryland, USA
Boat: 42' Sportfish
Posts: 3,356
Re: VHF-transmission identification challenge

Quote:
Originally Posted by CatNewBee View Post
There are regulations all station user has to comply to.
It is a voice based protocol.


All that sounds good on paper, but it's not always "complied with" and there no oversight to speak of.

Can't remember the last time I heard a VHF call sign around here...

-Chris
__________________
Selby Bay, South River, Chesapeake Bay, USA.
ranger42c is offline   Reply With Quote
Old 18-07-2018, 03:36   #14
Registered User
 
CatNewBee's Avatar

Join Date: Aug 2017
Boat: Lagoon 400S2
Posts: 965
Re: VHF-transmission identification challenge

Quote:
Originally Posted by Wotname View Post
RF surveillance experts tell me that every transmitter has it's own unique "fingerprint" for a the first few milliseconds after it is keyed. This is just a product of the transmitter coming up to its carrier frequency.

You would need some seriously expensive spectrum analysers and recorders to make use of this apparent fact.
That is true, but AIS has a different transmitter than the VHF at the navstation and VHF handhelds are completly separate devices too. With suveillance gear, you can potentially test a particular transmitter in the lab to tell, if it was likely used for a recorded transmission, as you can use voice spectrum analysis to recognise a person talking on the phone or on the VHF.

But to do it in real time and tell what vessel it is and who is talking, is a task for large agencies with high end equipment, nothing what a student can do with a vhf radio. I guess, the NSA and similar orgs probably can do this, they have the right gear and the necessary ressources to collect, categorize and store communications and digital fingerprints on voice calls.
CatNewBee is offline   Reply With Quote
Old 18-07-2018, 04:19   #15
Registered User

Join Date: Jul 2018
Posts: 4
Re: VHF-transmission identification challenge

Hello guys,

First of all thank you very much for your answers! This is highly appreciated

I will try to explain the situation/challenge a bit more so it gets more clear. What we did is create a program that catches VHF-signals on a specific channel, throws them through a language detection system (for Dutch and English) and then transcribes it into text. For now we have only tested it on commercial vessels - and at least in the near future we will continue to do so - because of the recurrent content of the conversations.

We can perfectly manage to turn the voice into text, at a surprisingly good success rate actually. However, the issue we face now is that it's just plain text without any interpretation possible. For the software to be able to have any real-world uses, we would need to link this transcript to a specific vessel so we know what party (vessel or shore) is talking. That way, in a next phase, we would be able to distinguish conversations vessel-to-vessel, vessel-to-shore or the other way around.

Do any of you know if, when a VHF-radio has DSC capability and a person engages a VHF-transmission over a regular VHF-channel, the MMSI-number gets sent over the DSC to channel 70 simultaneously? Or does DSC not get engaged in any way when using the regular VHF-communication? I know that, as far as commercial vessels go, almost all of them are equipped with DSC.

I have heard from several sources - none of them extremely reliable though - that the MMSI-number gets sent along to another channel with every VHF-radio 'activation' when the number has been programmed into the radio.

Furthermore, we have already looked at triangulation, but it would prove very difficult along the (straight) Belgian shoreline. There are some precedents though with the use of triangulation to located vessels in distress without DSC. One from the US Coast Guard in the Massachusetts Bay Area during the 1982 boating season, which is a pretty interesting read. (http://www.dtic.mil/dtic/tr/fulltext/u2/a129753.pdf)

The best alternative we have now is to 'hope' every transmission starts with (or contains) the vessel's name and then try to link it to a database of (expected) vessels to that specific port. But as already explained above, in theory there are a lot of rules regarding the style and content, but in practice those are rarely followed, making this a solution that's far from fool-proof.

I hope this explains the situation a little more. I'd be happy to provide more information if anyone wants to know more.
Anyways, I think it's an interesting project and hope we can find a way to label the conversations sooner or later

Cheers!
__________________

NicholasM is offline   Reply With Quote
Reply

Tags
transmission, vhf

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
Challenge: Wake Up The Mechanics - Outboard Challenge Ex-Calif Challenges 37 04-04-2016 08:55
Transmission Identification Help Please? Panaseaya Engines and Propulsion Systems 0 02-06-2013 07:25
VHF transmission issue ryderstk Marine Electronics 3 03-07-2011 14:32
Challenge: A Real Challenge Solved by a Forum Member Soft Air Challenges 10 27-03-2009 08:59
Hand held VHF and land transmission rsn48 Marine Electronics 17 02-11-2006 15:08



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 09:32.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2018, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.