VHF, DSC, etc.
by Daniel Piltch, Marine Computer Systems
 
(as originally published in Professional Mariner) 
  

 

It all used to be so simple. There was a VHF radio for short range communications and an SSB radio for long range communications. Now there are decisions to be made about DSC and GMDSS, VHF versus cellular, and even flowcharts to follow when responding to a distress call - if you're meant to respond at all.

Much of the confusion stems from a decision in 1979 by the International Maritime Organization to improve upon the marine communications available for safety and distress alerting as well as search and rescue operations. This led to the creation of the Global Maritime Distress and Safety System or GMDSS. One of the first things they did when creating this system, was to separate the world into four distinct and non-overlapping regions called Sea Areas. These Sea Areas correspond loosely to coastal, near-coastal, high seas and polar regions (see Table 1).

Table 1: GMDSS Sea Areas

Sea Area Approximate Range Description
A1 coastal up to 30 miles within range of coast VHF stations
A2 from A1 limit out to about 150 miles within range of coast MF stations
A3 70°N to 70°S, outside of A1 and A2 within range of Inmarsat satellites
A4 all other areas polar regions not covered by Inmarsat

Rather than base equipment carriage requirements on the size of a vessel, the GMDSS requirements are based on the vessel's area of operation. Even the largest coastal tanker need not be equipped with A3 type equipment if it never plans to be outside of area A2. On the other hand, any cargo vessel of 300 gross tons or more heading out onto the high seas must be equipped with all the equipment necessary to comply with the GMDSS requirements for Area A3.

However - there's a glitch in the plans. The US has not yet declared any operational A1 or A2 areas due to budgeting constraints and technical delays. This means that by default, all waters are part of Sea Area A3. In other words - since there are no A1 or A2 areas off the US coasts, but these waters do fall within the range of the operational A3 area, all US waters are part of area A3. Any SOLAS vessel required to comply with GMDSS should have been fitted for A3 type equipment as of February 1999 or have in hand a waiver from the Federal Communications Commission (FCC). Fortunately on November 20, 1998 the FCC issued a temporary blanket waiver for fishing vessels and small passenger vessels operating in US waters. This waiver is due to expire six months after areas A1 and A2 are established. Sea Area A2 is currently scheduled to be operational in Spring 2002 after many delays.

How Does Digital Selective Calling Fit Into the Picture?
Most of the equipment called for by GMDSS is not unfamiliar. It includes common items such as 406 EPIRBs, Inmarsat C, handheld VHF radios and search and rescue transponders (SARTs) for liferafts, as well as NAVTEX. However, it also includes some relatively new technology such as Digital Selective Calling (DSC) for VHF and MF/HF radios. Note the "selective calling" part of the name - this is the motivation for DSC's existence. It allows transmissions to be sent only to the appropriate stations. So when hailing a local coast guard station, their identifying number is punched into the radio before the call is made and the coast guard's radio will essentially "ring" to alert them of an incoming call. The same goes for ship to ship calls if the identity of the called ship is known. Of course distress alerts will ring radios in all reachable stations as well as on nearby vessels.

One of the nice add-on features of DSC is the ability for the radio to transmit the vessel's position if connected to a GPS receiver or similar device. This way, when the distress call goes out to all stations, the nearest coast guard station or Rescue Coordination Center (RCC) will know to take the lead in responding to the distress. If no RCC responds to the distress, other vessels will know how close they are to the scene of the distress as the calling vessel's position will appear on the radio screen and can act accordingly.

A key feature of DSC systems is the ability for the radio to store an Maritime Mobile Service Identity (MMSI) number in memory. This is a unique number assigned to each vessel and to each coast station. Vessels requiring an MMSI can apply for one from the FCC. Vessels that wish to have an MMSI, but are not required to have one (e.g., recreational vessels) BoatUS and MariTEL have been allowed to issue MMSI numbers and both are currently doing so for free. Generally, an MMSI number will be programmed into the radio upon installation and will not be changed.

The HF side of the system is complete, and the US Coast Guard has been maintaining a DSC watch on HF channels. However, the MF and VHF (Area A2 and A1) pieces have yet to be completed. The MF system is nearly up and running and should be available during 2002. The VHF system is much further behind. Other than a few test beds, the US Coast Guard has not yet begun to build out its DSC VHF network, and its not expected to be available before 2006 at the earliest.

The MariTEL DSC Network

Even though DSC VHF radios have been on the market for quite some time, and any new VHF radios are required to have DSC capability, the big red distress button on these radios is not likely to be heard by the USCG.

At least not directly. Since 1998, a private company has been hard at work building a DSC VHF network of their own. Due largely to the insight of Thom Belesky, Vice President of Advanced Technology and Engineering at New York-based MariTEL, the company began capitalizing on the advanced features DSC brought to the VHF network. MariTEL was already well known for the work in consolidating most of the local marine operators around the country used for patching VHF calls through to the telephone network. In fact, today MariTEL owns the license to nearly all of the VHF public correspondence frequencies in the US. They still operate this conventional operator assisted network for placing telephone calls to and from a regular (non-DSC) VHF radio.

While continuing to operate and improve this conventional network, they've been busy creating an entirely new infrastructure with the help of their partners American Tower Corporation - providing prime tower-top real estate on 161 radio towers up and down both coasts, Harris Corporation - providing integration and electronics for each of these remotely operated stations, Cubic Corporation - providing advanced directional VHF transmitters and receivers, and others who provide a fiber optic network with multiple links into the existing public switched telephone network (PSTN). Once active these 161 towers are expected to cover "nearly all of the nation's coastline and inland navigable waterways." Of interest to mariners in the Northeast is MariTELs definition of "nearly all of the nation's coastline," which so far doesn't include the coast of Maine which was quietly shut down when MariTEL purchased the station from a local operator.

In June of 2001, region one of MariTEL's new network was brought online. This region includes the Gulf of Mexico from Corpus Christi to Sarasota and the lower Mississippi up to Memphis. Offered in this initial rollout are direct dialed telephone calls from ship to shore (without operator assistance), as well as some additional features such as touch tone capability (say to check voicemail or a bank balance through an automated system) and vessel tracking. Soon to come is the capability to send data including emails or faxes by hooking a computer up to a MariTEL ready DSC radio.

One of the interesting uses of this new network is that ships that are out of direct line of sight range from each other can still have contact via VHF by having MariTEL complete the call through their network. Additionally, the home office can use the network to automatically poll a vessel or a group of vessels to determine their location.

The last published rates had most voice calls coming in at around $1.00 to $1.50 per minute depending on volume. Keep in mind that it's still a new system and things are likely to change - especially pricing.

The Cellular Competition

There are some who wouldn't even include cellular phones in an article discussing marine communications. "It's not for use on the water," they'd proclaim. The reality of the situation though is that cell phones are just about everywhere these days, and they do have their place on many inshore vessels. There are, however, several important differences that would suggest the use of VHF in some circumstances and cellular service in others.

One consideration is range. While not as much of a concern on inland rivers, service to handheld cell phones can drop off rapidly as little as a few miles off the coast. There are plenty of stories of unusually distant service being available, but it's generally not incredibly reliable. Keep in mind that cellular providers are constantly trying to maximize their capacity and one way to do this is to add new cell towers to existing coverage areas. When this happens, nearby towers will generally have their transmitting power reduced to avoid interference. Just because good coverage exists offshore today, there's no guarantee it will be there tomorrow. In fact, many providers see offshore coverage as a waste of resources that would be better directed at increasing the capacity of their shoreside customer base. VHF range is pretty consistent and will depend largely on coastal topography and antenna height, it's fair to expect coverage out to about 50-100 miles in most cases.

One way to increase your chance of getting cellular coverage offshore is to add a "bag style" phone along with an external antenna, the effective range of cellular service will be increased quite a bit. These bag phones with their larger batteries are capable of transmitting analog cellular signals using 3.0 watts of power compared to the 0.6 watts available from a handheld model. This increased power yields an effective signal from a farther distance offshore.

Perhaps the most important consideration when comparing VHF and cellular is the ability to transmit a distress signal. There are several aspects to this distinction. The Coast Guard does not monitor cellular communications, nor do other boats. You'll need to dial the appropriate USCG station directly (if you have the number) in order to summon them directly. Some cellular providers have started to conform to a shortcut dialing code (*CG) to reach the US Coast Guard, though this isn't the case in all areas. Even if you do get through directly, you don't have the benefit of having other vessels in your area listen in and provide assistance on the air.

The Coast Guard is not yet able to locate the source of a cellular signal, while VHF signals can be triangulated fairly easily with existing equipment. In the event that a position is mistakenly reported, the Coast Guard can quickly compensate if the distressed vessel is using a VHF radio.

And obviously, the special weather statements and safety broadcasts transmitted on channel 16 and 22A won't be left in your cellular voice-mailbox. You'll need to have a VHF radio in order to get

On the other hand, cellular phones provide an economical and easy way to keep in touch and are frequently relied on for personal communications. An advantage to having cell phones onboard for crew use is that the ship's VHF is less likely to be tied up for personal business.

A nice compromise is to sign up the vessel with MariTEL for communication with the home office and other ships in the fleet, while allowing crew to use their own cell phones for personal use when appropriate. This keeps the billing separate for business and personal communication.

The Satellite Competition

With satellite phone prices plunging, the most serious competition to MariTEL's near monopoly on coastal communication is the newer Low Earth Orbit (LEO) satellite systems such as Globalstar and Iridium. While neither is appropriate for distress communications for the same reasons outlined above, either one can be a valuable business tool for keeping communications costs down. This is especially true for vessels venturing beyond the nominal 100 mile VHF range. Handheld satellite phones can be had for $900 and below, and per minute prices are right around $1.50 with low monthly fees.

In a gesture showing an attitude of joining those you can't beat, MariTEL has signed up to resell some of these satellite services. This conveniently offers single billing for multiple communication modes.

When asked about the seriousness of the threat from these LEO systems, Jim Tindall, VP of Marketing at MariTEL responds that "gravity rules," suggesting that sooner or later significant amounts of capital will be needed to replace aging satellites while maintaining a terrestrial network of towers might be less expensive in the long run.

Another card that MariTEL is holding in its back pocket is that eventually, the Coast Guard will be interesting in activating Sea Area A1 and deploying a DSC VHF network. While they may choose to build their own competing network, it would likely be far easier to outsource this to MariTEL who is already in the process of building just such a network.

Perhaps time will tell whether MariTEL's fledgling network will survive in an increasingly competitive communications market. There's no doubt that no matter which company prevails in the market, the mariner will be the ultimate winner taking advantage of cheaper, better, and easier ways to communicate.

Table 2: Related web sites

MMSI numbers http://www.marinecomputer.com/articles/mmsi/mmsi.html
US GMDSS policy http://www.navcen.uscg.gov/marcomms/gmdss/
DSC  http://www.navcen.uscg.gov/marcomms/gmdss/dsc.htm
GMDSS Overview http://www.gmdss.com.au/index.html
International Telecommunication Union  http://www.itu.int/
International Maritime Organization http://www.imo.org/

 

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