B1P2

Question 1

What is meant by Time domain representation

Answer 1

how the strength of a signal varies over time
Can be representation mathematically as 
v(t)=A sin⁡〖(2πft)〗
or 
v(t)=A sin⁡(ωt + ∅)

ω is greek letter omega, and is called the angular frequency and is equal to 2πf
∅ is greek leter phi and is the phase of the signal. This describes the position of the waveform relative to time at 0 seconds
Phase is measured either in degrees or radians (rads) and 360 degress or 2π rad is equalvalent to a shift through a complete period

Question 2

What is meant by Frequency domain representation

Answer 2

frequency representation of a signal, also called the spectrum

Question 3

What is meant by fundamental frequency

Answer 3

The number of cycles of a periodic signal per unit time. The SI unit is the hertz (Hz), the number of cycles in one second. The fundamental frequency is the lowest frequency component in the signal; periodic signals other than sinusoids also have higher-frequency harmonics.

Question 4

What is the fourier series

Answer 4

The series of sinusoids into which a periodic signal v(t) can be broken down. A Fourier series has the general form

v(t) = A0 + A1cos(t + ) + A2cos(2t + ) + A3cos(3t + ) +…..+ Ancos(nt + n).

Question 5

3 basic digital modulation schemes are:

Answer 5

• amplitude-shift keying (ASK)
• frequency-shift keying (FSK)
• phase-shift keying (PSK)

Question 6

What is the fourier transform

Answer 6

– give the frequency domain representation of non-periodic signals

Question 7

What is a non-periodic signal

Answer 7

A signal that does not repeat at regular intervals of time. Compare ‘periodic signal’

Question 8

What are the properties of ASK

Answer 8

ASK is a special case of AM
Simple and low cost
Modulated signal can be generated by mixing or multiplying the carrier with the binary waveform

Question 9

What are the properties of FSK

Answer 9

FSK is a special type of FM

Bursts of a carrier wave at a second frequency are transmitted according to whether the data is 1 or 0

Question 10

What are the properties of PSK

Answer 10

Mode widely used
Many variations of PSK
Binary PSK or BPSK , 0 or 1 are represented by segments of sinusoids that differ in their phase

Question 11

What is meant by BER

Answer 11

The bit error rate BER is defined as the number of bits received in error divide by the number of bits transmitted, therefore a low BER is desirable

Question 12

What is a symbol

Answer 12

Generally, one of a distinct set of states selected from a finite set of possibilities

In the context of modulation, a symbol is a distinct waveform that can be transmitted over a channel. A symbol can represent one or more bits, depending on the modulation scheme used.
The relationship between the number of bits that can be repsented by a symbol, n, and the number of available symbols, M, is given by:
M = 2n

Question 13

What is baud

Answer 13

The term baud refers to the number of symbols per second, where one baud is one symbol per second

Question 14

What is Quadrature phase-shift keying (QPSK)

Answer 14

A method of digital modulation in which sinusoidal I and Q waves are combined to provide a set of symbols with discrete phase values. All symbols have the same amplitude in QPSK.

The preservation of the quadrature relationship between the I and Q waves, despite the inversion of either or both of the waves, means that both waves can be modulated using BPSK
I and Q waves are orthogonal to each other

Question 15

What us Quadrature amplitude modulation (QAM)

Answer 15

QAM combines QPSK with ASK techniques and introduces more amplitude levels as well as phases.
16-QAM scheme will perform better than 16-PSK scheme – that is, it has a better BER performance. This is the case for all QAM schemes compared to PSK.