Lectures 1 - 5

Question 1

Mobile phones and their base stations transfer and receive signals using which electromagnetic wave?

Answer 1

Radio Waves

Question 2

What frequency’s are used for typical AM Radio?

Answer 2

180kHz to 1.6MHz

Question 3

What frequency’s are used for typical FM Radio?

Answer 3

88MHz to 108MHz

Question 4

What frequency’s are used for typical TV?

Answer 4

470MHz to 854MHz

Question 5

What frequency’s are used for typical Mobile Phones?

Answer 5

900MHz to 2.1GHz

Question 6

Microwave Uses

Answer 6

Radar
Telecommunication Links
Satellite Communications
Weather Observation
Microwave Oven (operate at 2.4GHz - close to mobile frequency)

Question 7

What is the relationship between frequency and wavelength?

Answer 7

Velocity of light = Frequency x Wavelength

Question 8

Why is the mobile phone called a ‘cell phone’ in the USA?

Answer 8

This is due to the cell structure within which it operates

Question 9

What is a cell network?

Answer 9

A cell network contains a mesh of hexagonal cells which each have a base station in the centre. When within that cell your phone will connect to it.

Question 10

What does the size of the cell depend on?

Answer 10

Terrain - Signals are blocked by trees, buildings, hills
Capacity - The number of users in a given area
The frequency band of the network operator - Higher frequency = Smaller the cell

Question 11

What are the main components which form a cellular network?

Answer 11

Mobile Phone - Can move around
Base Station - Fixed in location
Mobile Switching Centre - Controls everything
The Public Switched Telephone Network (PSTN) - Connected to all other phones I.E. land lines etc

Question 12

How does the calling process work?

Answer 12

• The mobile phone sends a message to the Base Station, asking to be connected to a given telephone number.
• The Switching Centre detects the cell(s) nearest the mobile phone.
• The Switching Centre then connects the mobile’s signal to a channel on the PSTN.

Question 13

Why do we need Modulation?

Answer 13

• Voices would overlap

* There would be NO way of tuning into one radio station

Question 14

What is Amplitude Modulation?

Answer 14

Amplitude modulation (AM) is a method of impressing data onto an alternating-current (AC) carrier waveform.

The highest frequency of the modulating data is normally less than 10 percent of the carrier frequency.

The instantaneous amplitude(overall signal power) varies depending on the instantaneous amplitude of the modulating data.

Question 15

What is AM Demodulation?

Answer 15

A signal needs to be demodulated before it can be heard. This can be done using a diode, capacitor and full wave rectifier.

Question 16

Differences between FM and AM

Answer 16

AM - Modulates amplitude with constant frequency

FM - Modulates frequency at constant amplitude

Question 17

What are sidebands?

Answer 17

Each of two frequency bands either side of the carrier wave, which contain the modulated signal.

Question 18

What is FM Demodulation?

Answer 18

FM signals this can be done by passing the signal through a filter.

As the frequency shifts up and down, the amplitude of the signal coming out from the output of this filter also goes up and down, and this forms the basis of the audible signal.

In effect, the frequency variations are converted to amplitude variations.

Question 19

What is Frequency Division Multiple Access used for?

Answer 19

Method of handling multiple mobile phone channels at the same time.

Question 20

How does Frequency Division Multiple Access work?

Answer 20

• FDMA separates the available spectrum into distinct frequency channels by splitting it into uniform bits of bandwidth
• FDMA then puts each call on separate frequency sub-bands
• Thus the send and receive signals are at different frequencies

Question 21

What does Time Division Multiple Access do?

Answer 21

• TDMA separates each frequency channel into time slots
• Each voice conversation then gets a particular frequency channel and transmits its data in bursts, as a data stream of 1 and 0. There is thus more than one user in each frequency channel at any one time.
• Digital encoding is used to compress the data, helping to improve data transfer rates.

Question 22

What does SIM stand for?

Answer 22

Subscriber Identification Module

Question 23

What does Code Division Multiple Access?

Answer 23

• CDMA spreads digital data out over the entire available bandwidth. Multiple calls are overlaid on each other on the channel, with each assigned a unique sequence code. You don’t hear multiple conversations as codes are used to separate them.
• CDMA is a form of spread spectrum, which simply means that data is sent in small pieces over a number of the discrete frequencies available for use at any time in the specified range.

Question 24

What are the three types of mobile phone cells?

Answer 24

Macrocell (Large)
Microcell (Medium)
Picocell (Small)

Question 25

What does the size of the cell depend on?

Answer 25

The number of calls to be handled simultaneously | The physical terrain (buildings, hills etc)

Question 26

What is Wifi?

Answer 26

WiFi is a method to obtain a wireless RF connection to a Local Area Network (LAN), typically from a laptop to a wireless “hot-spot”.

Question 27

What is Bluetooth?

Answer 27

Bluetooth allows different electronic devices such as computer peripherals (mice and keyboards), mobile phones and wireless headsets to be connected together.

Question 28

What does GPS stand for?

Answer 28

Global Positioning System

Question 29

How does GPS work?

Answer 29

It uses a Network of 27 US military satellites, 24 of which are used to make calculations and 3 which are spares. These are in known locations. The time it takes for a signal from at least 4 satellites to reach the device is used to get the location, using a form of triangulation.