Topic 1

Question 1

Define a “System”

Answer 1

An integrated structure of hardware devices (e.g., electronic circuits, antennas, fiber optics, computer processors) and software algorithms (e.g., digital signal processing algorithms, network protocols) designed to achieve a specified function

Question 2

What happens to noise when transmission speed is increased, with nothing else changing.

Answer 2

The noise increases

Question 3

Define the term “Communication”

Answer 3

The transfer of information from one “point” to another “point” in space and/or time involving electronic transmitting/receiving/processing of information.

Question 4

Define the term “Analog communication”

Answer 4

Information is encoded as an analog signal (i.e., a continuous-amplitude continuous-time waveform over time).

Question 5

Define the term “Digital Communication”

Answer 5

information is encoded as a digital signal (i.e., a discrete-time sequence of finite-alphabet symbols).

Question 6

What does a Transmitter do?

Answer 6

Converts electronic signal into a form suitable for analog transmission through the propagation channel

Question 7

What does a Receiver do?

Answer 7

Performs the inverse of a transmitter in order to recover the original message signal

Question 8

What’s a channel?

Answer 8

The propagation medium (analog in nature) linking the transmitter and the receiver

Question 9

What are the 3 different types of channels?

Answer 9

• Wire-line channels (fiber optics & telephone cables)
• Wireless channels (Radiowave communication, visible light communication)
• Storage channels (CD, DVD)

Question 10

In what ways can transmitted signals be degraded when traveling through Analog mediums?

Answer 10

• Additive (thermal) noise
• Multiplicative noise (Rayleigh fading)
• Time-delayed multipath (intersymbol interference)

Question 11

How is Thermal noise produced at the receiver front end?

Answer 11

Thermally excited random motion of free electrons in a conducting medium such as a resistor

Question 12

What is the format of the information in a Digital communication system?

Answer 12

The message signal is in a digital form consisting of discrete symbols

Question 13

How is an analog information signal converted into a discrete-time & discrete-amplitude digital signal?

Answer 13

• Time sampling
• Amplitude quantization
  The resulting digitized information signal is modulated back into an analog waveform for propagation through the channel

Question 14

What is the performance criteria for Analog communication systems

Answer 14

Fidelity criterion such as signal-to-noise ratio, percent distortion, or expected mean square error (MSE) between transmitted and received waveforms.

Question 15

What is the performance criteria for Digital communication systems

Answer 15

The probability of incorrectly detecting a digit or a packet of symbols, i.e., the probability of error Pe

Question 16

Describe the Additive White Gaussian Noise (AWGN) channel.

Describe the properties of AWGN channel

Answer 16

The transmitted signal s(t) is corrupted by an additive white gaussian noise process n(t).

• The power spectral density (PSD) is constant N/2, as a function of frequency
• for any time instance t, the probability density function (pdf) of n(t) follows a Gaussian distribution.
• All white Gaussian noises are uncorrelated and independent

Question 17

Describe the LTI invariant filter channel

Answer 17

A linear time-invariant (LTI) system, which can be mathematically described by the impulse response of the system.

r(t) = s(t) (convoluted) h(t) + n(t)
https://bit.ly/3bKGXGp

Question 18

What can you say about the information with a signal that doesn’t change? How can information be carried in a signal?

Answer 18

A signal that doesn’t change doesn’t carry information! Information can be carried by the values and the rate of the changes.

Question 19

How do you determine the rate at which a signal changes? (in bits/s) - Shannon’s discovery

Answer 19

Given a transmitted power constraint P, a bandwidth W, and an additive white Gaussian noise (AWGN) channel with bilateral power spectral density (PSD) of N/2, then the channel capacity is given by:

C=W*log2(1+P/(WN)) bits/s

where P/WN is the signal-to-noise ratio or SNR

Question 20

When designing an analog communication system, what are the 3 characteristics which we need to consider?

Answer 20

• Reliability. The information in the message received is the same as the message sent.
• Efficiency in frequency spectrum & transmission power
• Simple in transmitter/receiver hardware & software