Introduction

Date: 2015-10-07; view: 425.

PART 1 (47.1 – 47.3.5)

Cellular radio systems

Ex.2 Who said this and what is meant by it?

Ex.1 Say whether the statements are true or false

Speech ex-s

UNIT 6 (PP.46-56)

1. Pilar knew that the diamonds had been stolen

2. The blood made Pilar feel ill

3. Stephen Farr acted on his father`s advice and came to look up Mr. Lee

4. Simeon Lee was a highly moral person according to Stephen

5. H. Poirot made certain insinuations against Mr. Farr

6. Stephen made a good impression on Johnson

7. Poirot wanted to have another short of questioning all members of the family

8. Simeon lee suffered from heard illness

9. Horbury never saw Mr. Lee diamonds and didn`t know they had been stolen

10. Johnson thought Horbury was a first-class lier and an unprepossessing person

Cellular radio systems are by far the most common of all public mobile telephone networks, the earlier (pre-cellular) networks now all being in decline. The basic principles of cellular systems were established by Bell Laboratories in 1949, but it was not until the early 1980s that technology allowed real commercial networks to be built and service offered to the public.

Systems were developed at different times in different countries and subject to a variety ofdifferent constraints such as frequency band, channel spacing etc. As a result, a number of different and incompatible cellular standards are in use throughout the world, and the more important standards are summarised later in this chapter.

Work is already well in hand to specify and develop second generation cellular systems, forwhich the opportunity is being taken to develop common standards and systems across several countries. One such notable system, GSM, has been developed in Europe, and is described in some detail later in this chapter.