Lesson 3

The Reading Module

Read the text: Telecommunications. Part III

Radio and television. Digital television standards and their adoption worldwide.

In a broadcast system, a central high-powered broadcast tower transmits a high-frequency electromagnetic wave to numerous low-powered receivers. The high-frequency wave sent by the tower is modulated with a signal containing visual or audio information. The antenna of the receiver is then tuned so as to pick up the high-frequency wave and a demodulator is used to retrieve the signal containing the visual or audio information. The broadcast signal can be either analogue (signal is varied continuously with respect to the information) or digital (information is encoded as a set of discrete values).

The broadcast media industry is at a critical turning point in its development, with many countries moving from analogue to digital broadcasts. This move is made possible by the production of cheaper, faster and more capable integrated circuits. The chief advantage of digital broadcasts is that they prevent a number of complaints with traditional analogue broadcasts. For television, this includes the elimination of problems such as snowy pictures, ghosting and other distortion. These occur because of the nature of analogue transmission, which means that perturbations due to noise will be evident in the final output. Digital transmission overcomes this problem because digital signals are reduced to discrete values upon reception and hence small perturbations do not affect the final output. In a simplified example, if a binary message 1011 was transmitted with signal amplitudes [1.0 0.0 1.0 1.0] and received with signal amplitudes [0.9 0.2 1.1 0.9] it would still decode to the binary message 1011 — a perfect reproduction of what was sent. From this example, a problem with digital transmissions can also be seen in that if the noise is great enough it can significantly alter the decoded message. Using forward error correction a receiver can correct a handful of bit errors in the resulting message but too much noise will lead to incomprehensible output and hence a breakdown of the transmission.

In digital television broadcasting, there are three competing standards that are likely to be adopted worldwide. These are the ATSC, DVB and ISDB standards; the adoption of these standards thus far is presented in the captioned map. All three standards use MPEG-2 for video compression. ATSC uses Dolby Digital AC-3 for audio compression, ISDB uses Advanced Audio Coding (MPEG-2 Part 7) and DVB has no standard for audio compression but typically uses MPEG-1 Part 3 Layer 2. The choice of modulation also varies between the schemes. In digital audio broadcasting, standards are much more unified with practically all countries choosing to adopt the Digital Audio Broadcasting standard (also known as the Eureka 147 standard). The exception being the United States which has chosen to adopt HD Radio. HD Radio, unlike Eureka 147, is based upon a transmission method known as in-band on-channel transmission that allows digital information to "piggyback" on normal AM or FM analogue transmissions.

However, despite the pending switch to digital, analogue receivers still remain widespread. Analogue television is still transmitted in practically all countries. The United States had hoped to end analogue broadcasts on December 31, 2006; however, this was recently pushed back to February 17, 2009. For analogue television, there are three standards in use. These are known as PAL, NTSC and SECAM. For analogue radio, the switch to digital is made more difficult by the fact that analogue receivers are a fraction of the cost of digital receivers. The choice of modulation for analogue radio is typically between amplitude modulation (AM) or frequency modulation (FM). To achieve stereo playback, an amplitude modulated subcarrier is used for stereo FM.

I. Reading exercises:

Exercise1. Read and memorize using the dictionary:

Broadcast tower, electromagnetic wave, low-powered receiver, visual or audio information, demodulator, broadcast media industry, integrated circuit, distortion, discrete values, binary message, forward error correction, video and audio compression, digital audio broadcasting, in-band on-channel transmission, analogue receiver, stereo playback, stereo FM

Exercise 2. Answer the questions:

1. What type of information does a signal contain?

2. What is the chief advantage of digital broadcast?

3. What are the three standards adopted worldwide?

4. Why is the switch to digital receivers made more difficult for analogue radio?

Exercise 3. Match the left part with the right:

1. HD Radio unlike Eureka 147 is based upon	1. on December 31, 2006.
2. The United States had hoped to end analogue broadcasts	2. a receiver can correct a handful of bit errors in the resulting message.
3. Using forward error correction	3. the elimination of problems of distortion are included.
4. For television	4. a transmission method known as in-band on-channel transmission.

Exercise 4. Open brackets using the right words:

ATSC uses Dolby Digital AC-3 for audio (transmission/compression), ISDB uses Advanced Audio (Coding/Decoding) (MPEG-2 Part 7) and DVB has no standard for (video/audio) compression but typically uses MPEG-1 Part 3 Layer 2.

The Speaking Module

II. Speaking exercises:

Exercise 1. Describe integrated circuit; noise; demodulator; binary message; amplitude modulation using the suggested words and expressions as in the example:

integrated circuit broadcast media industry; development; from analogue to digital broadcast; possible; more capable example: The broadcast media industry is at a critical turning point in its development with many countries moving from analogue to digital broadcast. This is made possible by the production of more capable integrated circuits.

noise distortion; nature; perturbations; final output

demodulator the antenna; is tuned; high-frequency wave; to retrieve; containing; information

binary message simplified example; with signal amplitude; would decode; reproduction

amplitude modulation the choice; between; stereo playback; subcarrier; stereo FM

Exercise 2. Ask questions to the given answers:

1. Question: ____________________________________ ?

Answer: For analogue television there are three standards in use.

2. Question: ____________________________________ ?

Answer: If the noise is great enough it can significantly alter the decoded message.

3. Question: ____________________________________ ?

Answer: The choice of modulation also varies between the schemes.

The Writing Module

III. Writing exercises:

Exercise 1. Complete the sentences with the suggested words: information; high-powered; tower; high-frequency; receivers

In a broadcast system, a central ______ broadcast tower transmits a ______ electromagnetic wave to numerous low-powered ______. The high-frequency wave sent by the ______ is modulated with a signal containing visual or audio ______.

Exercise 2. Fill in the table with words and expressions from the text:

	Method	Distortion	Standards
example: Digital broadcast includes the elimination of		snowy pictures, ghosting.
Radio is based upon
ISDB uses
All countries adopt

Exercise 3. Compose a story on one of the topics (up to 40 words):

“The advantages of Digital Broadcast”

“Three competing standards adopted worldwide”

“The destiny of analogue television”