# Signal Transmission

Task 1 – Learning Outcome2

L02.3 determine the bandwidth and expected information capacity of typical communication systems

Q1

(a) Describe the main factors upon which the maximum data rate over a channel depends.

(b) State the Nyquist Theorem and the Shannon Theorem for data channel capacity and explain the main difference between them.

(i) A telephone line has a bandwidth of 3000Hz. (300-3300Hz). The signal to noise ratio (SNR) is 35dB.

What is the theoretical highest bit rate transmission over the line?

(ii)A channel has a 1 MHz bandwidth. The SNR for this channel is 63dB.

What is the appropriate bit rate and number of signal levels?

L02.4 discuss the various channel impairments and theirresultant effect on the maximum system bit rate fordigital systems

Q2

There are several impairments in every channel besides those incorporated into Shannon’s Law. Discuss these and the effects they may have on the channel capacity.

Task 2 – Learning Outcome 3

L03.1 explain the need for modulation and the variety ofmodulation schemes used for analogue

Q3

(a) Discuss why radio frequency waves need a carrier wave for transmission. Expand your answer to develop mathematical expressions for

(i) An amplitude modulated wave

(ii) A frequency modulated wave

(b) An AM wave is represented by the expression :

v = 5 (1 + 0.6 cos 6280 t) sin 211 × 104 t volts

(i) What are the minimum and maximum amplitudes of the AM wave ?

(ii) What frequency components are contained in the modulated wave and what is the amplitude of each component?

L03.2 discuss the modulation methods used to representdigital data over analogue networks

Q4

Explain what you understand by the terms ;

(i) amplitude shift keying (ASK),

(ii) frequency shift keying (FSK),

(iii) phase shift keying (PSK),

Illustrate your answer in each case by considering a carrier wave being modulated by the following waveform;

L03.3 describe the range of digital modulation methods and typical applications

Q5

Various methods can be used to modulate pulse trains by analogue signals. Explain briefly the techniques used.

Describe, with the aid of diagrams, how

(i) Pulse Amplitude Modulation (PAM)

and (ii) Pulse Width Modulation (PWM) is achieved

Discuss the spectrum of each and how the modulating signal can be recovered.

L03.4 explain the reasons for multiplexing signals givingexamples of the methods used

Q6

Explain the term ‘multiplexing’ in general and describe why it is particularly important in the transmission of PAM signals.

Five different modulating signals are to be transmitted efficiently using PAM. Show how this can be achieved using time division multiplexing (TDM).

Your answer should contain a sketch of the system configuration and a waveform diagram showing how the sampled signals are time sequenced.

Task 3- Learning Outcome 4

L04.1 evaluate the nature of telecommunications traffic carried over circuit switched networks

L04.2 evaluate the nature of telecommunications traffic carried over packet switched networks

Q7

Describe what is meant by;

(a ) a circuit switched network

(b) a packet switched network

Illustrate your answer with diagrams and highlight the advantages and disadvantages of each.

Discuss the type or nature of telecommunications traffic which is carried over each network

L04.3 apply mathematical formulae to typical examples oftelecommunications traffic

Q8

(a) What do you understand by the terms;

(i) Erlang

(ii) Grade of Service (GOS)

(iii) Busy Hour Traffic (BHT)

(b) How many lines are required in a particular trunk group if 2 calls being blocked in every 100 calls attempted is tolerated and the Busy Hour Traffic is 10 Erlangs,

(c) What percentage of calls will be answered within 20 seconds if a call centre receives 650 calls in an hour of average duration 150 seconds and is manned with 34 available agents?

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