Automatic Identification System-2
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In order to ensure that the VHF transmissions of different transponders do not occur at the same time the signals are time multiplexed using a technology called Self-Organized Time Division Multiple Access (SOTDMA). The design of this technology is patented, and whether this patent has been waived for use by SOLAS vessels is a matter of debate between the manufacturers of AIS systems and the patent holder. In order to make the most efficient use of the bandwidth available, vessels which are anchored or are moving slowly transmit less frequently than those that are moving faster or are maneuvering. The update rate of fast maneuvering vessels is similar to that of a conventional marine radar. The time reference is derived from the navigation system.
Each station determines its own transmission schedule (slot), based upon data link traffic history and knowledge of future actions by other stations. A position report from one AIS station fits into one of 2250 time slots established every 60 seconds on each frequency. AIS stations continuously synchronize themselves to each other, to avoid overlap of slot transmissions. Slot selection by an AIS station is randomized within a defined interval, and tagged with a random timeout of between 0 and 8 frames. When a station changes its slot assignment, it announces both the new location and the timeout for that location. In this way new stations, including those stations which suddenly come within radio range close to other vessels, will always be received by those vessels.The required ship reporting capacity according to the IMO performance standard amounts to a minimum of 2000 time slots per minute, though the system provides 4500 time slots per minute. The SOTDMA broadcast mode allows the system to be overloaded by 400 to 500% through sharing of slots, and still provide nearly 100% throughput for ships closer than 8 to 10 NM to each other in a ship to ship mode. In the event of system overload, only targets further away will be subject to drop-out, in order to give preference to nearer targets that are a primary concern to ship operators. In practice, the capacity of the system is nearly unlimited, allowing for a great number of ships to be accommodated at the same time.
The system coverage range is similar to other VHF applications, essentially depending on the height of the antenna, but slightly better due to digital VHF and not analog VHF. Its propagation is better than that of radar, due to the longer wavelength, so it’s possible to “see” around bends and behind islands if the land masses are not too high. A typical value to be expected at sea is nominally 20 nautical miles (37 km). With the help of repeater stations, the coverage for both ship and VTS stations can be improved considerably.
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The system is backwards compatible with digital selective calling systems, allowing shore-based GMDSS systems to inexpensively establish AIS operating channels and identify and track AIS-equipped vessels, and is intended to fully replace existing DSC-based transponder systems.
Shore-based AIS network systems are now being built up around the world. One of the biggest fully-operational, real time systems with full routing capability is in China, operated by China MSA and delivered by Saab TransponderTech in Sweden. The entire coastline is covered with approximately 150 base stations and 50 computer servers. Hundreds of shore based users, including ca 25 VTS centers, are then connected to the network and been able to see the maritime picture, but also to communicate with the ship with SRM:s (Safety Related Messages). All data is in real time and will full safety and security of ships and port facilities.
Topic # 5. London – places of interest
London is really 3 cities: the City of London, the City of Westminster and the City of Southwark. Londonhas got a population of about 9 million people. That's 13 per cent of Britain' population. London stands on the River Thames. There are 27 bridges over the Thames in London and 8 tunnels under the river. London is 46 km from the north to south and 85 km from east to west.
There are many nice squares in London. Trafalgar Square is one of them and it is in the center of the West End. One can see a statue of Admiral Nelson in the middle of this square. The West End is the center of London There are many places of interest in the West End like the Houses of Parliament with its famous Big Ben. The West End is often calledWestminster.
The Houses of Parliament is the place where British Government is seated. The building is very beautiful with its two towers and a big clock called Big Ben. The Houses of Parliament was built in Gothic style in 1857 by architect Sir Ch. Barry. The original name was WestminsterPalace and it was the official residence of Royal Family until 16-th century. Then it became the meeting place for the Parliament.
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Westminster Abbey, where kings and queens were crowned, is opposite the H.P. This ancient building was founded in the 1050. Many famous people are buried here, among them I. Newton, Ch. Darwin, Ch. Dickens and R. Kipling.
The Clock Tower called Big Ben is 316 ft high and 40 ft square. People are allowed to get inside the Tower and can see the works of Big Ben. But there is no lift but only 340 steps up to Big Ben. The clock is very large: the minute hand is 14 ft long, the hour hand is 9 ft and the figures are 2 ft long. The clock weighs 13,5 tons
The Tower of London is very old building, it is more than 900 years old. English kings had lived in it for many years, but now it is a Museum. People like to go to the Tower. It was a fortress, a Royal House, a church, an arsenal and later a prison. The ravens are another famous sign, they live there. The legend says that if the ravens ever leave it, the Tower & London will fall. The palace at the Tower had its own Zoo. Henry III was given 3 leopards by German Emperor, a polar bear – by The King of Norway and the elephant – by the King of France. The lions from the Zoo appeared in Royal Arms of England as heraldic lions. In 1834 the Zoo was closed.
You can also visit the BuckinghamPalace. It's the London Home of the Queen. When the flag is flying on the top she's at home. The Palace was built in the 18-th century. Tourists like to see the Royal guard change.
All the historical places and famous parks are in the West End. The W.E. includes the shopping area of Knightsbridge, Oxford Street, Piccadilly Circus and fashionable Covent Garden. It hosts museums and galleries, among them are the Tate Gallery, the National Gallery, the National Portrait Gallery and BritishMuseum.
Topic # 6. Great Britain
The United Kingdom of Great Britain and Northern Ireland is situated on the British Isles. The British Isles consist of 2 large islands: Great Britain and Ireland, and about five thousand small islands. Their total area is over 244,000 square kilo-
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meters.
The United Kingdom is made up of 4 countries: England, Scotland, Wales and Northern Ireland. Their capitals are London, Edinburgh, Cardiff and Belfast respectively. But in everyday speech Great Britain is used to mean the United Kingdom. The capital of UK is London.
The British Isles are separated from the European countries by the North Sea and the English Channel. The western coast of GB is washed by the Atlantic ocean and the Irish Sea. The surface of the British Isles varies very much: the north of Scotland is mountainous and is called the Highlands, while the south, which has beautiful valleys and plains, is called the Lowlands; the north and west of England are mountainous, but the rest of the country – east, center and south-east parts – is a vast plain. Mountains are not very high: Ben Nevis in Scotland is the highest of
the mountains (1343m).
There are a lot of rivers in Great Britain but they are not very long: the Severn is the longest one, while the Thames is the deepest and most important one. The mountains, the Atlantic and Gulf Stream warm waters influence the climate of this country and as a result it is mild all year round.
The UK is one of the world’s smaller countries and its population is 57 million people. About 80% of the population lives in towns and cities. The UK is highly developed industrial country and it is known as one of the world’s largest producers and exporters of machinery, electronics, textile, aircraft and navigation equipment. One of the main industries of UK is shipbuilding.
The UK is a constitutional monarchy. In law, the Head of State is the Queen. In practice, the Queen reigns but doesn’t rule. The elected government rules the country with the Prime Minister at the head. The present Prime Minister name is Tony Blear. The British Parliament consists of two chambers: the House of Lords and the House of Commons. There are 3 main political parties in Great Britain: the Labour, the Conservative and the Liberal parties.
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Russia has good friendly relations with this country and we carry out mutually advantageous economic cooperation in different fields of economics.
Vocabulary:
The United Kingdom of Great Britain СоединенноеКоролевствоВелико-
and Northern Ireland – британиииСев. Ирландии
theBritishIsles – Британские острова
tobesituated – быть расположенным
toconsistof – состоятьиз
totalarea – общаяплощадь
respectively – соответственно
to include – включать
at the head – воглаве
chamber – палата
to separate – разделять
to wash – омывать
surface – поверхность
tovary – различаться, меняться
mountainous – гористый
valley – долина
vast – огромный, обширный
plain – равнина
deep – глубокий
to influence – влиять
mild – умеренный, мягкий
allyearround – круглый год
population – население
highlydeveloped – высокоразвитый
aircraft – самолеты
navigation – судоходство
equipment – оборудование
main – главный
shipbuilding – судостроение
constitutionalmonarchy – конституционнаямонархия
law – закон
inlaw – позакону
the head of the state –главагосударства
queen – королева
inpractice – фактически, на практике
toreign – царствовать, править
torule – править, управлять
toelect – выбирать
government – правительство
PrimeMinister – премьер-министр
The House of Lords – Палаталордов
The House of Commons – Палатапредставителей
goodfriendlyrelations – хорошие дружеские отношения
mutuallyadvantageouscooperation – взаимовыгодноесотрудничество
fieldofeconomics – областьэкономики
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