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127 notes > lecture 6 data&signals > Flashcards

lecture 6 data&signals Flashcards

1
Q

data can be either

A

analog or digital

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2
Q

analog data

A

the information is continuous and takes continuous values

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3
Q

digital data

A

the information is discontinuous, has discrete states and takes discrete values

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4
Q

examples of analog data

A
  • a clock with moving minute/hour hands

- sound of human voice

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5
Q

examples of digital data

A
  • a digital clock (goes from 8:05 to 8:06)
  • WhatsApp message
  • email
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6
Q

what is meant by discrete values

A
  • stored on the computer in the form of 0’s and 1’s
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7
Q

signals can be either

A

analog or digital

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8
Q

analog signal

A

has an infinite number of values in a range

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9
Q

digital signal range and levels

A
  • has a limited number of defined values in a range

- can have more than two levels

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10
Q

what is periodic analog signal

A
  • a signal which completes a pattern within a period of time

- repeats that pattern over subsequent identical periods

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11
Q

non-periodic digital signal

A
  • a signal that changes without exhibiting a pattern or repetitiveness
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12
Q

periodic analog signal can be classified as

A
  • simple or composite
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13
Q

simple periodic analog signal consists of:

A

one sine wave, and it cannot be decomposed into smaller signals

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14
Q

composite periodic analog signal:

A

it is composed of various sine waves (combination)

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15
Q

peak value=

A

sqrt2 x root mean square value (rms)

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16
Q

period(s)=

A

T=1/F (inverse of frequency)

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17
Q

frequency(Hz)=

A

F=1/T (inverse of period)

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18
Q

peak value is called

A

the amplitude

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19
Q

frequency refers to

A

how many cycles (oscillations) per second

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20
Q

period refers to

A

the time taken for one cycle (oscillation)

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21
Q

frequency and change

A
  1. change over a short period of time = higher frequency
  2. change over a long period of time = lower frequency
  3. no change = frequency equals zero
22
Q

phase shift

A

how much you shifted from time 0

23
Q

radians=

A

degrees * pi/180

24
Q

a cycle represents

A

2 pi’s and 360 degrees

25
Q

frequency and wavelength

A
  1. the higher the frequency, the smaller the wavelength

2. the lower the frequency, the bigger the wavelength

26
Q

frequency domain represents

A

a periodic sine wave using a single vertical line

27
Q

why is a single frequency sine wave not

useful in data communications?

A

because we need to send a composite signal, which is a combination of sine waves of different frequencies, amplitudes and phases

28
Q

If the composite signal is periodic, the

decomposition gives

A

a series of signals with discrete frequencies

29
Q

if the composite signal is non-periodic,

the decomposition gives

A

a combination of sine waves with continuous frequencies

30
Q

bandwidth(Hz)=

A

maximum frequency - minimum frequency

31
Q

example of non-periodic composite signal

A
  • AM and FM radio stations
32
Q

number of bits per level=

A

Log2(level)

33
Q

the more bits you can encode

A

the faster the data rate

34
Q

a digital signal is a composite analog

signal but..

A

it has an infinite bandwidth

35
Q

why is that what is sent, may not be what is received (what causes this effect)

A
  • because of the bandwidth supported by the medium
36
Q

baseband (unfiltered) transmission of a digital signal, that preserves its shape, is possible only if..

A

we have a low pass channel with an infinite or very wide bandwidth

37
Q

what is a low pass channel

A
  • a channel that allows frequencies that are near zero to be transferred
  • e.g BASEBAND
38
Q

bits and bandwidth in baseband transmission

A
  • bandwidth is proportional to the bit rate

- to send bits faster, we need more bandwidth

39
Q

which type of signal does baseband transmit?

A

DIGITAL

40
Q

which type of signal does bandpass transmit?

A

ANALOG (CONVERT DIGITAL 2 ANALOG)

41
Q

two types of channels

A
  • baseband

- bandpass

42
Q

transmission process in a bandpass channel

A
  1. input digital signal
  2. convert to analog
  3. pass through the bandpass channel
  4. convert to digital
  5. digital signal output
43
Q

three causes for transmission impairment

A
  1. distortion
  2. attenuation
  3. noise
44
Q

what is attenuation

A

amplitude has decreased

45
Q

how to try to fix attenuation

A

by amplification

46
Q

problem with amplification

A

will increase noise (MORE JUNK)

47
Q

what is distortion

A

sent signal differs from received signal

48
Q

what is noise

A
  • unwanted signal(s)
49
Q

what is SNR

A

power of signal to power of noise ratio

50
Q

SNR(dB)=

A

power of signal/power of noise

51
Q

SNR (converting to dB)

A

10Log10(SNR)

52
Q

what device converts analog and digital signals to the other

A

MODEM

MODULATOR & DEMODULATOR

127 notes (11 decks)

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