Monday, May 26, 2008

AIS 2.0: The Next Version

Data communications required to implement eNavigation are likely to overwhelm the capacity of the 10-year-old design of AIS. The next version of AIS should not only address this constraint, it should also act as back-up, both for AIS and for VHF voice communications, while reducing ship operators satellite telecommunications costs.

AIS is gradually becoming an inte­gral part of the aids that mariners use to conn a ship, not yet as important as Radar and GPS but probably about on par with VHF. Ships are already required to carry at least two radars, and it now seems likely that they will be required to carry a terrestrial system like eLoran as a backup for GPS.
Do we need a backup for AIS too? To the extent that mariners have started us­ing AIS target information for collision avoidance, the answer is yes. Mariners already rely on AIS for the name and position of a ship when hailing a it via VHF, and I wouldn't be surprised if mariners are also using (T)CPA derived fromAIS data for collision avoidance, because it generally is more accurate and up-to-date than (T)CPA derived from radar.
Voice VHF, too, should have a back­up system. Inadvertent keying on an operational channel blocks all calls, and interference makes VHF calls very hard to understand in some areas.

The major reason we need AIS 2.0 is throughput capacity. Using AIS for messaging is still at an early stage but it is clear that it should be the primary method, rather than voice VHF, to convey important safety related in­formation to the mariner, because it is both more efficient and more effec­tive to communicate this information. Examples of information that can be communicated by messaging include traffic advisories, such as the location of other vessels, navigation hazards, hydro and meteorological informa­tion, traffic organization information, including lock order, procession through one-way channels.

Aids to Navigation
There are serious efforts underway to formulate standard AIS safety related messages that will convey this informa­tion and display it for the mariner, in the context of the situation at hand, on an ECDIS or an enhanced Radar screen. Some of these efforts have already been completed, including Aids to Naviga­tion (AtoN) messages and messages that address regional safety issues in places such as the Strait of Malacca or the Great Lakes. The US Coast Guard is currently in the process of formulating regional safety related AIS messages, and we can expect that eNavigation will not only require the transmission of safety related messages but also the transmission to government authorities of ship, voyage, cargo and passenger reports including customs, immigration and cargo clearance reports, port state, agricultural, health and other inspec­tion reports and hazardous materials reports.

All will use the meager 19.2 kbps throughput capacity available with AIS 1.0. In some areas, however, condi­tions are already reaching the point where AIS cell size will be reduced to accommodate just the regular AIS message traffic, ships positions and identifications. The system needs more capacity to fully realize the po­tentially significant benefits of safety messaging and to streamline reporting to government authorities.

The system also needs more through­put capacity to allow relaying of AIS messages from one station via another station. Relaying messages is not pos­sible with AIS 1.0 because doing so would take too much of the throughput capacity, especially in dense ship traf­fic areas.

Additional throughput capacity, unfortunately, doesn't come easily. Operators will need additional Radio Frequency Spectrum as well as additional hardware, both shore-side and on ships.

You might be able to avoid acquiring additional spectrum and installing new hardware if you use satellite communica­tion infrastructure already installed on most ships. Satellite communications, however, have the disadvantage of being expensive, mostly because the cost of building and launching satellites and operating land earth stations needs to be recovered in per-kilobytes toll charges. Also, shipboard satellite equipment is expensive to install and maintain. These costs are serious impediments to using satellite communications for AIS 2.0 purposes. Satellite communication cost was a major stumbling block in the implementation of Long Range Identification and Tracking (LRIT).

Designating more 25 KHz VHF channels to AIS might be easier, politically, than acquiring spectrum bandwidth in a higher frequency range, but it will not be enough to provide the required increase in throughput capacity and would still require new hardware.

The WiMAX Solution
Beyond using SatComm and ad­ditional VHF channels for AIS, what are your options?

One option that deserves to be con­sidered is the more modern Worldwide Interoperability for Microwave Ac­cess (Wi MAX) protocol, which uses a higher frequency. It can achieve a range of about 15 NM (line-of-sight) and can easily achieve throughput of 1.5 megabit per second (mbps) or 80 times more than AIS. In fact, WiMAX was designed to handle up to 75 mbps for Metropolitan Wide Area Networks (MWAN). WiMAX currently requires a base station, but could be adapted to operate between ships if one of them assumes the role of a base station, as we now do with AIS 1.0.
WiMAX uses spectrum bandwidth 3 times more efficiently than AIS. WiMAX's spectrum efficiency in terms ofbits per second per Hertz is between 1 and 1.5. In comparison, theAISprotocol has a spectrum efficiency of only .38 bits per second per Hertz. This means that a throughput of 1.5 mbps could be achieved with WiMAX within about 1.25 MHz of spectrum bandwidth.
Regardless of the need for AIS 2.0, ships that are in port or at anchor near shore are likely to start using WiMAX to substitute for expensive satellite communications.
If WiMAX is also used for AIS 2.0, there already are well-established methods to give priority to safety related messages: "Quality of Service" (QoS) and "Differentiated Services" (Diff Serv). They will ensure that WiMAX general telecommunications traffic doesn't interfere with higher priority safety-related message traffic.
While underway WiMAX's through­put capacity would be used to back-up AIS 1.0, for safety related messaging and forreporting to government authorities. It could even provide backup for VHF voice communications through Voice over IP (VoIP).
In the future, WiMAX will also al­low ships to automatically establish a "Mobile Ad-hoc Network" (MANet). This is a major step beyond relaying of AIS messages from one station to another. It has the effect of increasing the range of Wi MAX well beyond 15 NM in areas where there is dense ship traffic such as the English Channel and the Strait of Malacca. Dense traffic in this context means that many of the ships in the area are within WiMAX range of each other. Coincidentally, AIS safety related messaging to support eNaviga­tion would likely be in high demand in these very same areas.
ITU recently adopted WiMAX as a worldwide standard (ITU-R M.1457) and there already are a number of ven­dors who sell the necessary hardware, so, unlike AIS, we won't have to start from a clean sheet. Instead we will be able to take advantage of the economies of scale inherent in a well-established industry standard.

WiMAX limitations
WiMAX also has its limitations: Unlike AIS, and because of its higher frequency, WiMAX is limited to strictly line-of-sight communications. To compensate WiMAX repeaters will need to be installed to provide coverage around capes and islands that are close to shipping channels.
Also, if we are going to rely on WiMAX's much higher throughput capacity for safety messaging, then what would be its back-up? AIS 1.0 will not be able to handle safety messaging in dense ship traffic areas without signifi­cant AIS cell contractions. Although costly, satellite communications could provide WiMAX backup for safety messaging on ships that already have this equipment on board. Voice VHF would be the backup for WiMAX AIS safety messaging for ships that do not have satellite communications equip­ment on board.

WiMAX Spectrum
WiMAX technology is readily available today. Acquiring spectrum bandwidth for marine safety and for reporting to government authorities will be much harder. Major mobile phone service companies are spending billions to acquire spectrum for their customers. The maritime industry cannot com­pete on that scale. It might be possible, however, to negotiate co-existence on a spectrum band that is currently used by land earth stations for earth-to-space communications because land earth stations typically are more than 15 NM in-shore.
AIS will grow in importance as an aid to navigation, even more so with the addition of safety messaging in the framework of eNavigation. AIS will need more capacity to accommodate such safety messaging and it also needs a redundant system to become a truly reliable aid to navigation. It will not be possible to use AIS for transmission of reports to government authorities without increasing the avail­able throughput capacity.
The advent of WiMAX creates an opportunity to achieve these goals without imposing new car­riage requirements but, instead, use public-private partnerships.
We can expect that ship operators will start to realize that they can sig­nificantly reduce their satellite com­munication cost by using WiMAX when in port or at anchor near shore. This will create business opportunities for port administrations to provide ship operators with WiMAX service by investing in the necessary shore-side infrastructure.
Now is the time to start spectrum negotiations and to formulate minimum WiMAX equipment requirements to ensure that ship operators investments in WiMAX equipment will also increase AIS capacity and, simultaneously, pro­vide a back-up for both AIS and voice VHF.