1.    a)     Broadband and mobile networks are under increased pressure during the current coronavirus outbreak, as many activities are taking place virtually and   remotely.   The   UK   communications   regulator   Ofcom   recently published  a  number  of  tips  to  help  families  and  businesses  manage effectively during this time, including the following: 10

.    Use your landline or Wi-Fi calls if you can.

.    Move your router clear of other devices.

.    Lower the demands on your connection.

.    Try wired rather than wireless.

.    Plug your router directly into your main phone socket.

.    Don’t use the microwave when you’re making video calls, watching HD videos or doing something important online.

.    Disconnect devices that are not in use.

Use your knowledge of communications to explain the reasoning behind each of these tips in as much technical detail as you can. Use no more than 500 words.

2.    Two bandpass  signals  are  shown in Figure 2 below: DSB-SC and AM with 100% modulation, for two different message signals.

a)    Which of the two  signals represents DSB-SC and which represents AM  with 100% modulation? Explain your reasoning. 5

b)    For  each of these bandpass  signals, sketch their respective approximate spectra, labelling them “DSB-SC” and “AM” . 5

c)    Given the carrier used in both cases has a frequency of 455 kHz, sketch the message signal (in the time domain) in both cases (DSB-SC and AM), clearly indicating the fundamental period on both plots. 5

3.    a)     A periodic signal x(t) can be approximated using the first  10 terms of its Fourier Series expansion as follows: 5

x(t) is used to frequency-modulate a 50 MHz sinusoid with a modulation index  of  5.  Find  expressions  for  the  maximum  frequency  and  phase deviations of the resulting signal and find an expression for the approximate baseband and bandpass bandwidths.

b)    Show that the NBFM expression for a single tone message can be written as a scaled version of 5

Sketch the above signal in the time and frequency domains, and comment on the bandpass bandwidth.

c)    Discuss 3 possible approaches for the demodulation of NBFM, describing in as much detail as possible how each approach works. Use no more than 300 words. 10

d)    Consider the following scenario: 5

You are being detained in a prison cell, with no access to any electronic devices nor to the outside world. Another engineer is detained in another cell on a different floor. You discover that you are able to communicate with this person by knocking your metal spoon against the water pipe at night when the complex is silent.

You have with you a hand-drawn map of the prison complex, and you have an urgent need to deliver this to the other person. Using your knowledge of communications, devise a simple and effective strategy to convey this map to the other prisoner as quickly as possible. The only items available to you are paper, pencil, a ruler, a metal spoon, a toothbrush, a mirror, a blanket, a pillow, and your lecture notes from ELEC202. You can assume the other person has similar items available to them, and can respond to you with spoon knocks.

4.    Figure Q4 shows how the bit error rate (BER) of selected digital transmission systems is related to the signal-to-noise ratio (Eb/No).

Figure Q4 – Bit error rate of selected digital transmission systems. BBB = bipolar baseband; UBB = unipolar baseband

a)    A  particular  baseband  communication  scenario  stipulates  a  maximum tolerable error rate of 1 bit in 10,000. The choice of signalling format is determined by the signal power available at the transmitter. 5

Use Figure Q4 to determine which signalling format would require the least power, commenting on the relative requirements of the two: unipolar and bipolar baseband signalling.

b)    Explain  what  factors  govern  the  maximum  rate  at  which  data  can  be communicated error-free  across  a  channel  and  discuss  some  of  the implications of this. Present your answer in as much detail as possible, using sketches and diagrams to help illustrate your point where relevant, and stating any assumptions made. Use no more than 200 words. 10