Wireless беспроводной

Задания

Задание 1. Прочитайте и переведите текст.

The speed of light is of relevance to communications. For example, given the equatorial circumference of the Earth is about 40,075 km and c about 300,000 km/s, the theoretical shortest time for a piece of information to travel half the globe along the surface is 0.0668 s.

When light is travelling around the globe in an optical fiber, the actual transit time is longer. Furthermore, straight lines rarely occur in global communications situations, and delays are created when the signal passes through an electronic switch or signal regenerator. A typical time as of 2004 for a U.S. to Australia or Japan computer-to-computer ping is 0.18 s. The speed of light additionally affects wireless communication design.

Another consequence of the finite speed of light is that communications between the Earth and spacecraft are not instantaneous. There is a brief delay from the source to the receiver, which becomes more noticeable as distances increase. The communications delay between Earth and Mars is almost ten minutes. As a consequence of this, if a robot on the surface of Mars were to encounter a problem, its human controllers would not be aware of it until ten minutes later; it would then take at least a further ten minutes for instructions to travel from Earth to Mars.

This effect forms the basis of the Global Positioning System (GPS) and similar navigation systems. A position on Earth can be determined by means of the delays in radio signals received from a number of satellites, each carrying a very accurate atomic clock, and very carefully synchronized. To work properly, this method requires that (among many other effects) the relative motion of satellite and receiver be taken into effect, which was how (on an interplanetary scale) the finite speed of light was originally discovered.

Задание2. Ответьте на вопросы:

1. What is of relevance to communication?

2. Do straight lines occur in global communications situations?

3. Are communications between the Earth and spacecraft instantaneous?

4. How can a position on Earth be determined?

5. Are radio signals received from satellites or Martians?

Вопросы к практическому занятию

1. Можете ли вы сказать, о чем текст, основываясь на заголовке? Выскажите предположения.

2. Какие слова и словосочетания относятся к общенаучному стилю?

3. Озаглавьте каждый абзац текста так, чтобы заголовок выражал основную идею абзаца.

4. Изложите основное содержание текста.

Практическое занятие 6