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SNADA Final > Communication Theory > Flashcards

Communication Theory Flashcards

1
Q

noise

A

unwanted signal pertubation that is always present

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2
Q

internal noise

A

thermal, shot, flicker

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3
Q

external noise

A

atmospheric, extra-terrestrial, man-made

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4
Q

noise power from thermal noise

A

Pn = kT 𐤃f

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5
Q

k variable value

A

1.38e-23

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6
Q

𐤃f =

A

bandwidth

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7
Q

RMS voltage

A

en = sqrt(4kT𐤃fR)

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8
Q

noise power with a resistor

A

Pn = (en/2)^2/R

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9
Q

converting to dB

A

10log(P1/P2)
20log(V1/V2)

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10
Q

noiseless system NR = ? NF = ?

A

NR = 1 NF = 0

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11
Q

NR =

A

(S/N)in / (S/N)out

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12
Q

NF =

A

10log(NR)

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13
Q

Noise ratio for cascaded system

A

NR = NR1 + NR2-1/P1 + … NRn-1/(P1P2…Pn)

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14
Q

what stage dominates in a cascading system

A

first

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15
Q

SNR max =

A

input signal / power of thermal noise

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16
Q

effective noise =

A

noise performance

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17
Q

effective noise =

A

Te = Pn/(PgkB)

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18
Q

relationship between noise ratio and noise temperature

A

F = 1+ Te/To Te = To(F-1)

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19
Q

all amplifiers introduce

A

some noise

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20
Q

bandwidth =

A

range of frequencies

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21
Q

bandpass filters

A

remove noise and channel interference

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22
Q

modulation

A

impressing the signal onto a carrier wave so it can be transmitted at the carrier frequency

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23
Q

when the carrier frequency is ____________ transmition signal is ____________

A

higher, lower

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24
Q

passband filters

A
  • excludes excess noise
  • modulates on a higher frequency without interference
  • multiple transmitters can operate at the same time without frequency
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25
Q

modulation equation

A

v(t) = Vp*sin(wt+phi)

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26
Q

Vp

A

amplitude

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27
Q

sin(wt)

A

frequency

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28
Q

phi

A

phase

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29
Q

modulation can be

A

analogue or digital

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30
Q

AM

A

change in amplitude

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31
Q

FM

A

change in carrier frequency

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32
Q

PM

A

change in phase

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33
Q

FM and PM are also called

A

angle modulation

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34
Q

amplitude is related to the

A

modulating signal

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35
Q

carrier constant of AM signal

A

Accos(2pi*ft)

36
Q

amplitude modulated carrier wave =

A

m(t)cos(2pift)

37
Q

amplitude modulation pros/cons

A

pros: used for envelope detection -> simple and cheap

cons: transmitter needs a lot of power -> expensive

38
Q

amplitude modulation equation

A

AM = [Ac+m(t)]cos(2pift)

39
Q

in AM, message signals can be recovered using

A

envelope detection

40
Q

modulation does what to the spectrum

A

shifts it either right or left

41
Q

upper sideband limit

A

USB = fc+fm

42
Q

lower sideband limit

A

LSB = fc-fm

43
Q

fc>= W

A

avoids overlap

44
Q

fc=W

A

main carrier frequency

45
Q

fc/W >1

A

avoid distortion

46
Q

AM envelope condition

A

(Ac+m(t))>0

47
Q

envelope detection condition as mp is peak amplitude

48
Q

AM modulation index

49
Q

inequality for envelope detection based off modulation index

50
Q

coherent detection condition

51
Q

prerec for undistorted envelope

52
Q

tone modulation index

53
Q

modulation index for multi-tones

A

u = u1+u2+…+un

54
Q

efficiency power

A

n = useful/total
n = Ps/(Dc+Ps)
n = Pm/(Ac^2+Bn)

55
Q

tone modulation power efficiency

A

n = u^2/(2+u^2) * 100%

56
Q

am coherent

A

translates frequency of sidebands back to baseband

57
Q

DSB-AM coherent detection oscillation

A

oscillating source needs to be oscillating at the same frequency as the carrier source

58
Q

RC conditions

A

RC>1/fc
RC<1/W

59
Q

RC for an AM envelope =

A

RC = sqrt(1/Wfc)

W = message signal bandwidth

60
Q

clearly defined envelope conditions

A

wc>2piW
wc= 2pif

61
Q

DC components can be

A

blocked by high pass filters

62
Q

ripples can be reduced by

A

low pass filters

63
Q

Voice AM examples

A

emergency services, taxi, military, airport

64
Q

generalised carrier signal

A

x(t) = Ac cos(wt+θ)

65
Q

angular frequency

A

wi = dθ(t)/dt

66
Q

phase angle

A

θ(t) = integral from -infinity to t (wi(a))da

67
Q

varying the angle

A

encodes info of phase on carrier signal

68
Q

phase deviation

A

𐤃θ = km(t)

69
Q

peak phase

A

𐤃θ = |km(t)|

70
Q

FM angular frequency

A

wi = wc +km(t)

71
Q

frequency deviation

A

𐤃f = k/2pi * m(t)

72
Q

power of AM modulated wave

A

power = Ac^2 /2

73
Q

power of an am modulated wave is dependent on

74
Q

max frequency deviation in FM

A

𐤃w max = kf*mp

𐤃f = k/2pi * mp

75
Q

bandwidth of an angle modulated signal is

76
Q

bessel functions

A

Jn(D) = (-1)^n*Jn(D)

77
Q

as bandwidth increases in the FM spectrum

A

spread increases
power of carrier frequency decreases

78
Q

AM signals

A

low bandwidth
low efficiency
no info in the carrier transmission

79
Q

FM signals

A

complex
high efficiency
wide bandwidth
better noise performance

80
Q

multiplexing

A

combines signals from different sources

81
Q

sideband filters help

A

avoid overlap

82
Q

FDM example

A

broadcast radio

83
Q

FDM

A

signals seperated in frequency
occuplied limited portion of channel
occupy allocated frequency always
band-limited to avoid overlap

84
Q

TDM

A

seperated in time
access to the entire channel
fraction of total time is allocated
used to multiplex digital signals

85
Q

Xfm =

A

Accos(2pi(fct)) + Am/2cos(2pi(fc+fm)t)+Am/2cos(2pi(fc-fm)t)

SNADA Final (2 decks)

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