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ECOMM (FINAL) > Introduction to Communication System > Flashcards

Introduction to Communication System Flashcards

1
Q

What is communications?

A

Transfer of information from one place to another.

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2
Q

What is the supposed characteristic of communications?

A

Should be efficient, reliable and secured.

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3
Q

What is communication system?

A

Components act together to accomplish information transfer.

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4
Q

What is electronic communication system?

A

Transmission, reception, and processing of information between two or more locations using electronic circuits.

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5
Q

How many forms an information source can be in? List them.

A

Two:

(i) Analog form.
(ii) Digital form.

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6
Q

Why is communication important?

A

Exchange of information between two parties separated in distances in a more faster and reliable way.

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7
Q

What is information?

A

The commodity produced by the source for transfer to some user at the destination.

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8
Q

What is message?

A

The physical manifestation of information as produced by the information source.

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9
Q

What is signals?

A

A physical embodiment of information voltage signal or

current signal.

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10
Q

Analog vs. Digital

A
  1. Analog
    - Continuous variation.
    - Assume the total range of frequencies\time.
  2. Digital
    - Takes sample:
    (i) non continuous stream of
    on/off pulses.
    - Translates to 1’s and 0’s.
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11
Q

Advantages of Analog (2)

A
  1. Smaller bandwidth
  2. Synchronization problem is
    relatively easier.
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12
Q

Disadvantages of Digital

A
  1. Larger bandwidth.
  2. Synchronization problem is
    relatively difficult.
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13
Q

Advantages of Digital (4)

A
  1. Inexpensive.
  2. Privacy preserved ( data
    encrypted) .
  3. Can merge different data.
  4. Error correction.
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14
Q

Disadvantages of Analog (4)

A
  1. Expensive.
  2. No privacy preserved.
  3. Cannot merge different data.
  4. No error correction capability.
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15
Q

Communication System Model diagram:

A

Refer to file named final in ecomm file.

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16
Q

Communication System Model components:

8

A
  1. Source.
  2. Input Transducer.
  3. Transmitter.
  4. Channel.
  5. Receiver.
  6. Output Transducer.
  7. Destination.
  8. Signal Waveform Distortion.
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17
Q

What’s the function of source?

A

originates a message (human voice, a television picture, an email, or data message, or data).

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18
Q

What’s the function of input transducer?

A

Converts nonelectric (human voice, email text, TV video) into an electric waveform called a message or baseband signal using physical devices (microphone, a computer keyboard, or a camera

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19
Q

What’s the function of transmitter?

A

Modifies the baseband signal for efficient

transmission and may consist of A/D converter, an encoder, and a modulator. Receiver-demodulator, decoder and D/A.

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20
Q

What is channel?

A

Medium that convey the electric signals at the
transmitter output over a distance e.g. twisted copper wire telephone and DSL, coaxial cable television and internet, optical fiber or radio link.

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21
Q

What’s the function of receiver? (2)

A
  • Reprocesses signals received from the channel by
    reversing signal modifications made at the transmitter.
  • Removal of noise due to channel.
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22
Q

What’s the function of output transducer?

A

Converts electric signal to its original form (Message).

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23
Q

What is destination? (2)

A
  • Unit to which message is communicated.
  • Channel behaves like a filter by attenuating the signal (vary with channel length) and distorts the transmitted waveforms.
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24
Q

What’s the factor of signal waveform distortion?

A

Due to physical phenomena

such as frequency dependent gains, multipath effects and Doppler shifts.

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25
Q

What is the basic requirements of communication system? (4)

A
  1. Rate of information transfer.
  2. Purity of signal received.
    (Whether the signal received is the same as the signal being transmit)
  3. Simplicity of the system. (the simpler the system, the better)
  4. Reliability.
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26
Q

Elements of Communication Systems (CS)

A

Refer to file named final in ecomm file.

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27
Q

Information of CS elements:

3

A
  1. The communication system exists to convey a message.
  2. Message comes from information source.
  3. Information forms - audio, video, text or data.
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28
Q

Transmitter of CS elements:

5

A
  1. Processes input signal to produce a transmitted signal that suited the characteristic of transmission channel.
  2. E.g. modulation, coding, mixing, translate.
  3. Other functions performed amplification , filtering, antenna.
  4. Message converted into electrical signals by
    transducers.
  5. E.g. speech waves are converted to voltage
    variation by a microphone.
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29
Q

Channel (transmission media) of CS elements:

2

A
  1. A medium that bridges the distance from source to destination. Eg : atmosphere (free space), coaxial cable, fiber optics, waveguide.
  2. Signals undergoes degradation from noise , interference and distortion.
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30
Q

Receiver of CS elements:

4

A
  1. To recover the message signal contained in the
    received signal from the output of the channel,
    and convert it to a form suitable for the output
    transducer.
  2. E.g. mixing, demodulation, decoding.
  3. Other functions performed: Amplification,
    filtering.
  4. Transducer converts the electrical signal at its input into a form desired by the system used.
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31
Q

What is modulation? (2)

A
  • A process of changing one or more properties of the analog carrier in proportion to the information signal.
  • One of the characteristics of the carrier signal is changed according to the variations of the modulating signal:
    (i) AM - amplitude, E
    (ii) FM - frequency, ω
    (iii) PM - phase, θ
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32
Q

Why is modulation is important? (5)

A
  1. To generate a modulated signal suited and compatible to the characteristics of the transmission channel.
  2. For ease radiation and reduction of antenna size.
  3. Reduction of noise and interference.
  4. Channel assignment
  5. Increase transmission speed.
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33
Q

What is noise?

A

Unwanted signals that coincide with the desired signals.

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34
Q

How many types of noise are there? List them.

A

Two types:

(i) Internal noise.
(ii) External noise.

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35
Q

What is internal noise?

A

Caused by internal devices/components in the circuits.

36
Q

What is external noise? (2)

A
  1. Noise that is generated outside the circuit.

2. E.g. atmospheric noise, solar noise, cosmic noise, man made noise.

37
Q

What is interference? (4)

A
  1. Contamination by extraneous signals from human sources.
  2. E.g. from other transmitters, power lines and
    machineries.
  3. Occurs most often in radio systems whose receiving antennas usually intercept several signals at the same time.
  4. One type of noise.
38
Q

What is distortion? (2)

A
  1. Signals or waves perturbation caused by
    imperfect response of the system to the desired signal itself.
  2. May be corrected or reduced with the help
    of equalizers.
39
Q

Limitations in Communication System (Technological Problems):
(2)

A
  1. Includes equipment availability, economic factors, federal regulations and interaction with existing systems.
  2. Problem solved in theory but perfect solutions may not be practical.
40
Q

Limitations in Communication System (Physicals Limitations):

A
  1. Bandwidth limitations:
    (i) Measure of speed.
    (ii) The system ability to
    follow signal variations
    depends on the
    transmission
    bandwidth.
    (iii) Available bandwidth
    determines the
    maximum signal
    speed.
41
Q

Limitations in Communication System (Noise Limitations):

3

A 
1, Unavoidable.
2. The kinetic theory.
3. Noise relative to an
information signal is
measured in terms of signal
to noise ratio (SNR).
42
Q

Communication system design is compromise within:

A
  1. Transmission time and power.
  2. SNR performance.
  3. Cost of equipment.
  4. Channel capacity.
  5. Bandwidth.
43
Q

What is cycle?

A

One complete occurrence of a repeating wave (periodic signal).

44
Q

What is frequency?

A

The number of cycles of a signal that occur in one second.

45
Q

What is period?

A

The time distance between two similar points on a periodic wave.

46
Q

What is wavelength?

A

The distance traveled by an

electromagnetic (radio) wave during one period.

47
Q

Wavelength (λ) formula:

A

λ = 300/f.

48
Q

[Optional] Extremely Low Frequencies:

A

30Hz to 300 Hz.

49
Q

[Optional] Voice Frequencies:

A

300Hz to 3kHz.

50
Q

[Optional] Very Low Frequencies:

A

3kHz to 30kHz.

51
Q

[Optional] Low Frequencies:

A

30kHz to 300kHz.

52
Q

[Optional] Medium Frequencies:

A

300kHz to 3MHz.

53
Q

[Optional] High Frequencies:

A

3MHz to 30MHz.

54
Q

[Optional] Very High Frequencies:

A

30MHz to 300MHz.

55
Q

[Optional] Ultra High Frequencies:

A

300MHz to 3GHz.

1GHz and above = microwaves

56
Q

[Optional] Super High Frequencies:

A

3GHz to 30GHz.

57
Q

[Optional] Extremely High Frequencies:

A

30GHz to 300GHz

58
Q

How many types of communications are there? List them.

A

Four:

  1. Simplex.
  2. Duplex.
  3. Half duplex.
  4. Full duplex.
59
Q

What is simplex?

A

One-way channel.

60
Q

What is duplex?

A

Two-way Channel.

61
Q

What is half duplex?

A

Alternate TX/RX

62
Q

What is full duplex?

A

Simultaneous TX/RX.

63
Q

Types of communications diagram (simplex, duplex, etc.)

A

Refer to file named final in ecomm file.

64
Q

What are the communications signal variations?

A
  1. Baseband.

2. Broadband.

65
Q

What is baseband?

A
  1. The original information signal such as audio, video, or computer data.
  2. Can be analog or digital.
66
Q

What is broadband?

A

The baseband signal modulates or modifies a carrier signal, which is usually a sine wave at a frequency much higher than the baseband signal.

67
Q

Various forms of communication system:

4

A
  1. Broadcast: radio and television.
  2. Mobile communications.
  3. Fixed communication system-land line.
  4. Data communication-internet.
68
Q

What is the frequency spectrum of a waveform consist of?

A

Consists of all frequencies contained in the waveform and their amplitudes plotted in the frequency domain.

69
Q

What is the bandwidth of a frequency spectrum?

A

The range of of frequencies contained in the spectrum. It is calculated by subtracting the lowest frequency from the highest.

70
Q

Voltage amplifier formula:

A

A v = V o /V i

71
Q

Transistors current gain formula:

A

β = i c / i b

72
Q

Chain pulley block formula:

A

Weight lifted/Weight applied.

73
Q

Transformer formula:

A

Secondary voltage/Primary voltage

74
Q

Gear box formula:

A

Output torque/Input torque.

75
Q

What is Power gain? What is its formula?

A

It is the ratio of output power over input power.

A p = P o /P i

76
Q

Power gain is always < = 1, if

A

the energy consumed in doing a work.

77
Q

Example of power gain less than one:

A

transformer, chain pulley block, gear boxes, etc.

78
Q

In amplifiers: (power gain)

3

A
  1. The apparent power gain may be more than one.
  2. The signal power is amplified.
  3. DC electric power is transformed into signal power.
79
Q

In signal gain:

3

A
  1. The advantage of, signal gain may be >1 though the
    power gain is < 1.
  2. At first instance, it appears that there is no apparent relation between signal gain and power gain.
  3. It is because the friction of the load in which the power is fed, is not accounted.
80
Q

Power gain in communication formula:

A

Power gain in dB = 10 log (P o /P i ) dB

81
Q

Voltage gain in communication formula:

A

Voltage gain in dB = 20 log (V o /V i ) dB

82
Q

In communication, if:

power gain, voltage gain

A

Power gain < 1, voltage gain <1.

83
Q

Relation between power gain and voltage gain formula:

A

P o /P i = (V o /V i )²

(P o /P i ) dB = = 2(V o /V i) dB

84
Q

Power gain formula (alternatively):

A

Power gain = 10 ^ (gain in dB/10)

85
Q

Voltage gain formula (alternatively):

A

Voltage gain = 10 ^ (gain in dB/20)

ECOMM (FINAL) (2 decks)

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