SHARE-LOC
WAP-based maritime location system
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Project students: Enseigne de vaisseau Guilhem DESVIGNES Enseigne de vaisseau Gaetan LUCAS de COUVILLE
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Introduction
The International Maritime Organisation (IMO) has been trying to improve the security at sea for decades. As time goes on, the maritime traffic remains the most important one and ships are larger and larger. Some super-tankers reach more than 500,000 tons. But as the tonnage of ships increases, so does their inertia. It means that it takes more and more time to stop a ship, or even to change its course. Paradoxically, the number of people onboard is decreasing. Nowadays, the Officer Of the Watch (OOW), who is the man in charge of the nautical security, can be alone on the bridge. Thanks to electronic and computer science, OOW have at their disposal many new navigation instruments. Among those, let us quote the Automatic Radar Plotting Aids (ARPA), and the Electronic Chart Display and Information System (ECDIS). ARPA is a RADAR that enables the tracking of ships, and gives important information such as the Closest Point of Approach (CPA). ECDIS is the internationally adopted system for presentation of electronic chart data on a computer screen, and intended to replace paper charts as the legal base for safe navigation. However, although ECDIS are very efficient and useful, ARPA has a large amount of weaknesses. First of all, in case of rough sea, smaller ships can be mistaken with sea echoes. Moreover, the tracking of ships with the ARPA is very limited because of target swapping. In order to take the best account of the dynamic environment, a new system, the Automatic Identification System is now appearing. It is a technology that makes possible the identification and tracking of ships from other ships and from shore stations. The AIS is comparable to aeronautics transponders but while planes have been equipped with transponders for a while, AIS is a relatively new technology and it is still not currently used by maritime navigation. While this system is very promising, it needs a consistent logistic that can not be carried by all ships. In order all ships to have similar on-line location information about all others ships, a solution on the basis of more conventional approach to the data collection and dissemination is required. In a period in which the development of communication terminals is as important as the one of development of networks, the obvious approach for finding a solution to this problem is to use the existing mobile phone's technology. Indeed with the advance of the Wireless Application Protocol (WAP) the mobile phones today are capable of retrieving and displaying large amounts of data and some graphics stored on a web server. The WAP devices are able to contact the server and read/write information using dial-in connection, which make the deployment of on-line information easy to implement. The need for sharing real-time location information and easy to deploy on smaller ships information system led to the idea of making a Real Time Ship Location Information System using Automatic Identification System Data and WAP-Enabled Mobile Phone User Device. We called this system the Share-Loc system.
I.1-The Automatic Identification System
AIS stands for Automatic Identification System. AIS is a technology that appeared in the mid-nineties and which is comparable to aeronautic transponders. In a couple of year, the AIS will be imposed to largest ships and to ships carrying a large number of passengers.
A ship fitted with an AIS receives navigation data sent by surrounding ships, by the means of its maritime VHF. Those data include the name of the ship, its length, its speed and its position. They come from different sources such as data coming from GPS or data coming from the speed meter. These data items provide useful information for the Officer Of the Watch (OOW) who can thereafter take appropriate decisions to avoid any collision. These data are also exploited by shore based Vessel Traffic Services-stations (VTS) which can also prevent collisions or in the unfortunate case of a collision organise more efficiently a search and rescue action.
All data received by an embarked AIS are exploited by specialised application software, providing similar functions than those of technologies such as ARPA or ECDIS. Those software calculate some important navigation data and give valuable information to the OOW using an electronic computer interface. Let us mention the Closest Point of Approach (CPA) and the Time before CPA (TCPA). The most cost-effective way to display AIS data is to have a radar-like display on a PC with AIS targets only including their information presented where bearing and distances to the targets could be compared and identified on the radar. Moreover, AIS data could be presented on an ECS or an ECDIS It is also possible to superimpose a RADAR (or ARPA) image, with an ECS image and at last with the AIS.
Figure 1: An AIS layer superimposed with a RADAR image and an electronic chart
I.2-WAP
The Wireless Application Protocol (WAP) is a result of the WAP Forum's efforts to promote industry-wide specifications for technology useful in developing applications and services that operate over wireless communication networks (http://www.wapforum.org/). The WAP specifies an application framework and network protocols for wireless devices such as mobile telephones, pagers, and Personal Digital Assistants (PDA). These specifications extend and leverage mobile networking technologies (such as digital data networking standards) and Internet technologies (such as ML, URLs, scripting, and various content formats). This effort aims at enabling operators, manufacturers, and content developers to meet the challenges in building advanced differentiated services and implementations in a fast and flexible manner.
More specifically the objectives of the WAP Forum are:
- To bring Internet content and advanced data services to digital cellular phones and other wireless terminals (URLs, HTML pages…).
- To create a global wireless protocol specification that will work across differing wireless network technologies.
- To enable the creation of content and applications that scale across a very wide range of bearer networks and device types (GSM, GPRS…).
- To embrace and extend existing standards and technology wherever appropriate.
The WAP Forum was created in 1997. Nowadays, it regroups more than 90 percent of the handset manufacturers. Two times a year, it gives specifications and recommendations concerning the WAP protocol itself, the Wireless Markup Language (W.M.L.) and its "Micro-Browser", the Wireless Telephony Applications …
As compared to conventional Internet, wireless networks are different in the following manner:
Users' needs on mobile phone are much more different than that of the PC users. This decides the type of application that will be used for the wireless network. Users don't focus on their handset the way they do when they are sitting in front of a desktop computer. Therefore, devices must be extremely simple and easy to use. Applications built for these devices must therefore present the best possible user interface for quick and simple usage. As soon as professionals step out of the office, information needs and desires change. Wireless Internet subscribers will not want to use their handset to "surf the Internet." They will have small, specific tasks that need to be accomplished quickly.
2) The Network is different:
As compared to Internet, wireless data networks tend to have
- Less bandwidth
- More latency
- Less connection stability
- Less predictable availability. Furthermore, as bandwidth increases, the handset's power consumption alsoincreases. Therefore, even as wireless networks improve their ability to deliver higher bandwidth, the power availability at the handset will still limit the effective throughput of data to and from the device. A wireless data solution must be able to overcome these network limitations and still deliver a satisfactory user experience.
3) The devices are different. Due to strong limitations of battery life and form factor, wireless devices tend to have:
- Less powerful CPUs,
- Less memory (ROM and RAM)
- Restricted power consumption
- Smaller displays (3 to 4 lines at a time)
- Different input devices (e.g., a phone keypad, voice input, etc.)
Because of these limitations, the user interface of a mobile phone is fundamentally different than that of a PC. The limited screen size and lack of a mouse requires a different user interface metaphor than the traditional desktop GUI. Nevertheless, the implementation of faster mobile phone networks and the emergence of the third generation of mobile system moderate the last statements (the potential of these new technologies is detailed in section III.3.1.)
The WAP programming model (Figure below) is similar to the WWW programming model. This provides several benefits to the application developer community, including a familiar programming model, a proven architecture, and the ability to leverage existing tools (e.g., Web servers, XML tools, etc.). Optimizations and extensions have been made in order to match the characteristics of the wireless environment. Wherever possible, existing standards have been adopted or have been used as the starting point for the WAP technology. WAP content and applications are specified in a set of well-known content formats based on the familiar WWW content formats. Content is transported using a set of standard communication protocols based on the WWW communication protocols. A micro browser in the wireless terminal co-ordinates the user interface and is analogous to a standard web browser.
Figure 2: Principles of a WAP application
II-Share-Loc
The Share-Loc system is a ship-location monitoring system that targets all ships that can not be fitted with AIS. Furthermore, because users must be within the range of the mobile network base stations in order to be able to communicate at all, the Share-Loc system works only near the coast line where the mobile network antennas are. The system targets small sailing boats and little motorised pleasure boats, which are unlikely to have AIS. Nevertheless, those categories of ships are of great importance to the Share-Loc system because, firstly, it is impractical for them to have AIS and, secondly, their number is more important than the number of ships fitted with AIS, especially near the coast line. The Share-Loc system deals with constantly changing information and allows answers to simple queries to be delivered to the end user's device (usually WAP enabled mobile phone). In order to be able to incorporate this feature, the implementation of the system must use dynamic WEB pages prepared 'on the fly', i.e. prepared on request. In order to build dynamic WEB/WAP pages, several technologies are considered. The technology we have chosen to build the Share-Loc system was the SUN solution. This solution is an open and free technology that presents the advantages of using servlets, all the API of the Java language, free Web server (Tomcat-Jakarta project) and free Wap gateway (the Kannel project).
Figure 3 : Design of the prototype
According to figure above, three main components complete the database, the server and the application server:
- The registration part, which is just an Internet application.
- The WAP alternative to the AIS, which is a WAP application.
- The VTS application, which simply establishes a connection between the VTS and the database
The Share-Loc system incorporates seven categories of physical components. Among them, there are three different devices, a server, a gateway, an application server and a database.
- The mobile device that is used by sailors (end users) to send and receive data. There are no particular specifications for this device, except the fact that it must be WAP enabled and compatible with the WAP release 1.1.
- A personal computer (PC) that is used by sailors to access to WEB pages in relation to the Share-Loc system. On those pages, users can have (and supply) information concerning the Share-Loc system. They must also register on the so-called "registration page" in order to use the Share-Loc system.
- A computer containing the VTS application. This device can be a simple PC. It is used for the display of ships fitted with AIS or using Share-Loc.
- The server used is the Tomcat release 4 from Apache (http://jakarta.apache.org/). This server is absolutely free, and enables the storage and implementation of the servlets. That is why all the servlets and HTML or WML files are stored on this server.
- The gateway is used to convert wml files into compact binary format understood by the client and vice versa. The gateway we use is free and comes from the Kannel project (http://www.kannel.3glab.org/).
- The application server holds a thread that updates the data stored in the database. It is obvious that this thread must always run.
- A MySQL database server (http://www.mysql.com/). MySQL is one of the most used databases in the world. It is fast, easy to install and implement and it is an Open Source Software (OSS) so it is a free software in fact.
III-Results and discussion
III.1-WAP alternative to the AIS
In order to summarize the main achievements of our WAP prototype, the main functions given by the Share-Loc to the mobile device of a final are as follows:
Display of navigational information about external boats that also use a Share-loc system (in a given region of interest). Several possibilities are offered to the users:
- the user can have information about all ships surrounding him within 20 Nautical miles
- the user can choose to have information on a boat just by giving its name
- The user can have information (confirmations) about his estimated own position.
- The user can have information about harbors that are in the database.
- The user can have information about main lighthouses that are in the database.
- The user can be linked to a selection of Wap sites.
The WAP alternative to the AIS as it is developed is actually ready to be used: concerning this release, no bugs were reported. But in fact, most of the functions that are at the disposal of the user necessitate regular manual updates, which is bothering for users. Considering the recommendations made by the IMO, real-time update of dynamic data must be done at least one time per ten seconds for a ship sailing between 0 and 14 knots. With the WAP real updates are made manually with sometimes up to one hour of difference. Of course, an estimate update of the position is done between two manual updates, but strong currents, and winds can lead to very important drifts. Moreover, the heading and the speed are just manually updated. A change in the course, or in the speed that has not been noticed could lead to important position errors. It is important to notice that changes in course or speed frequently happen with pleasure boats. Actually, the maintenance of frequent manual updates -that are considered as being the only true dynamic data of the ship- is too restricting for users. Even a manual update each half-hour is not enough to have a accurate position of the ship. All dynamic data -such as position- and all calculated data -such as CPA- are thereafter not enough precise to be used by sailors in order to prevent collision. In this present release, dynamic information delivered by the server are just general information that can be useful in case of bad weather, or to give some information about the position of a friendly ship, wherever she is in the world. We have to recognize, however, that this work is very useful and lays the foundations of the next generation of systems delivering information to hand-held mobile devices. Indeed, in a couple of month, phones fitted with GPS will be available on the market. Real updates could be done as often as necessary and the WAP alternative to AIS will become very attractive. It is possible to instruct GPS to give the position of the user automatically and with simple additional calculations to deduce the COG (Course Over Ground) and the SOG (Speed Over Ground) while taking account drifts due to current or wind at the same time. The next generation of mobile hand-held devices will thus be able to compete with the AIS in terms of precision.
Figure 4: The Nokia emulator displaying the main card of the prototype
III.2-VTS application
In order to resume the main achievement of the VTS application, it can be say that all computers of VTS centres will be linked to a same database. VTS stations will then be able to:
Have information about all ships that use a Share-loc system (in a given region of interest) and AIS (in their area).
- Visualize those information on an Electronic Chart (on their area only).
- Send harbour messages to the database.
The VTS application is comparable to the software used for AIS . As such we believe that its potential is interesting and valid for many VTSs. The display of ships using either AIS or Share-Loc on the same screen, and moving in real-time gives a very efficient interface and a decision-aided system for security purposes.
Figure 5: A screenshot of the VTS application
III.3-On-line applications
The main objective of our project was to build a system that is able to replace the AIS for smaller ships. As the time went on, it became obvious that the use of mobile networks and web development tools could provide far more features to the application than there were in the original outline of the project. In order to demonstrate some of the capabilities provided by the on-line information, we included in the shareloc system the following capabilities :
- sending on-line information about harbours.
- sending on-line information about lighthouses.
In fact, two important properties of database systems are essentials to our prototype: a) the capability of the database to store very large amounts of data and b) the possibility for designated people to modify those data.
A good example of the possibilities WAP can offer is the possibility to make a reference to pages containing information about the harbours close to the ship's location. The WAP pages are pre-prepared by third party developers, but web-link in our system allows access to this information. Indeed, we succeeded in making a short program where harbour managers can set all the data concerning their harbour and make it available to all interested parties. Information content such as the number of empty "boat park", or the tide-time are very interesting for the sailor. This program has been developped at the end of the project so it must just be considered as an example of what can be made. It is based on the same principles that the application VTS and illustrates the range of applications our prototype can support.
Those sorts of on-line applications that provide services from a company to a user are really the future of WAP, and are the direction next researches should concentrating on...
IV-Further work
The end of the second generation of mobile phones is marked by the emergence of new network technologies, and new mobile devices. The GPRS (General Packet Radio Service) is the very new technology that appeared on the market just a few months ago. It is an evolution of the GSM approach that allows transfer of packets of data with a theoretical maximum speed of up to 171.2 kilobits per second (kbps). This technology is interesting because it provides a real Internet access, as HTTP and FTP protocols will be enabled. Nevertheless, the maximum speed announced above is very unlikely to be reached unless very particular conditions. The maximum speed of 56 kbps is more reasonable as an expectation, taking into account that even this speed might be reduced from time to time due to disruptions of the service.
Another technology, the EDGE (Enhanced Data rate for GSM Evolution) needs further attention. The EDGE technology is different from the GPRS one, but the theoretical speed of 384 kbps is, once again, unlikely to be reached. The speed that will be reach by EDGE will be better than the one actually reached by GPRS, but user will have to change their mobile devices to access this new network.
Whatever the technology used, mobile devices will become more and more complex and powerful. Thanks to such improvements, it will be easy to have accurate dynamic data and an automatic update of the database. Estimations of the dynamic data of a boat will thus be done in case of loss of signal. The third generation of mobile network is likely to appear first in Japan. The implementation of very high-speed networks such as UMTS (Universal Mobile Telecommunication System) will launch this new generation.
With more than 2 Mbps speed widely available expected, there are actually more expectation at the moment than concrete advances in this area. Above all, the license price of such a system, and its implementation is still out of price for almost all the users and telecom operators.
The opportunities that the third generation mobile devices would provide are enormous: let us mention the videophone, the downloading of games, MP3, pictures, the access to enterprises Intranet etc. Such technologies could provide far more applications for the Share-Loc system. Users could thus be able, for example, to watch a video or photos of a given area...
Conclusion
I fact, Share-Loc is a solution that could lead everyone to have an AIS or its equivalent. For the moment, it is obviously difficult to use this release; nevertheless, everything is ready for the implementation of new technologies. Indeed, in the next decades, we will see the appearance of very powerful new handset devices with much more memory, colour screen... Share-Loc will be absolutely able to adapt to all new technologies in order to provide much more attractive pages, with pictures sounds and even videos if needed. But the most important thing will be the possibility to have access to GPS data or even to have an incorporated GPS in the mobile phone. This could lead to a very interesting release of Share-Loc, as interesting as AIS. But, actually, the WAP alternative to the AIS must not be considered as the final objective. Far more applications can be realised by using all the services provided and developed on the Internet. Harbours and lighthouses examples presented in this release could be generalized by using database that have ever been made by services such as the SHOM in France.
Moreover, as the Internet has been becoming a huge shop for a few years now, the e-commerce is also appearing on mobile devices. Share-Loc can easily provide services such as the booking of free rooms in harbours...
Possibilities are infinite, and will be in fact limited to the imagination of service providers Whatever the technologies and the options that will be taken, Share-Loc is just waiting for manufacturers to build more powerful and cheaper mobile devices for becoming a really interesting and useful tool for all sailors.
