Final Exam Flashcards
(141 cards)
1
Q
10log(A*B) = ?
A
10log(A) + 10log(B)
2
Q
10log(A/B) = ?
A
10log(A) - 10log(B)
3
Q
10log(10) in nonDB
A
10
4
Q
10log(9) in nonDB
A
222 = 8
5
Q
10log(6) in nonDB
A
4
6
Q
10log(3) in nonDB
A
2
7
Q
10log(30) in nonDB
A
1000
8
Q
what is the mixer equation
A
fIF = fRF +- fLO
9
Q
what is a mixer used for?
A
to upconvert or downconvert
10
Q
what affects the transconductance of diodes?
A
LO (local oscillator)
11
Q
what is LO?
A
local oscillator
12
Q
what is IF (desired output signal)?
A
intermediate frequency
13
Q
what is IF (undesired output)?
A
image frequency
14
Q
what is a double balance mixer?
A
a switch driven by the LO that reverses the polarity of the RF input at the LO freq
15
Q
what are the findings of a double balance mixer (4)?
A
1) +LO half cycle biases 2 diodes ON
2) LO shorted to gnd
3) connects lower right point to gnd
4) RF travels through load resistor
16
Q
fIF is also equal to?
A
mfRF +- nfLO
17
Q
what introduces IMs for amplifiers
A
non-linearities
18
Q
for amplifier linearity, the slope of the line is
A
the gain
19
Q
what are IMs
A
intermodulations
20
Q
FDMA
A
frequency division multiple access
21
Q
approach of FDMA?
A
divide into frequency bands
22
Q
exampled of FDMA?
A
AM or FM radio
23
Q
constraint of FDMA?
A
spectrum/guardband
24
Q
AM envelope equation
A
E(t) = Ac + m(t) >=0, for all t
25
definition of modulation index (myu) (u)
ratio of the peak value of the message signal to the amplitude of the carrier
26
mod idx (u) equation
u = mpeak / Ac, 0<=u<=1
27
AM power efficiency using "basic" AM eqn
n = useful power/total power
or
n = Ps/Pc+Ps
28
RC time constant equation
RC = sqrt(1/Bfc)
- fc: carrier freq (kHz)
- B: bandwidth (kHz)
29
what does DSB-SC stand for?
double sideband suppressed carrier
30
observations of a DSB-SC plot
- AM signal has 2x bandwidth of original modulated signal
- information in sideband is redundant (can suppress one sideband (single sideband/SSB)
31
what is FM? definition?
Frequency Modulation
- microphone displacement creates a voltage that drives voltage controlled oscillator that modulates frequency
32
what does beta B stand for?
FM modulation index
33
key observations of an FM spectrum
- FM bandwidth increases as beta increases
- changes frequency, not amplitude
34
Carsons bandwidth/rule eqn
BW = Betac = 2(beta+1)*fm [Hz]
- Betac: carson bandwidth
35
how much does carsons bandwidth accounts for?
98% of total power
36
how to calculate for unaccounted power after carsons bandwidth?
10log(1-0.98) = -17dB
37
FM vs AM attributes
amplitude sensitivity? FM yes, AM no
noise immunity? FM is higher
required BW? FM > 20x AM; FM is larger
38
Giga
10^9
39
Mega
10^6
40
real sampling nyqist: 1 ADC ____________
running at 2x highest freq content
41
I/Q sampling nyquist: 2 ADCs ___________
running at 1x highest freq content
42
what does I and G stand for in I/Q sampling?
I: in-phase component
Q: Quadrature (90 degrees) component
43
real sampling magnitude: amplitude based on one sample = ?
can't! need samples over a whole period
44
I/Q sampling magnitude: amplitude based on one sample = ?
sqrt(I^2 + Q^2)
45
I/Q magnitude approximation method:
sqrt(I^2+Q^2) = max[I,Q] + 1/2min[I,Q]
- absolute values of terms
46
real sampling ________distinguish _________
can't; positive vs negative frequency
47
I/Q sampling ________ distinguish ______
can; positive vs negative feedbackw
48
what does heterodyne/heterodyning mean?
mix/mixing
49
super heterodyne
LO > RF
50
super-heterodyning:
fLO,max/fLO,min = (fc,max + fIF) / (fc,min + fIF)
51
heterodyning:
fLO,max/fLO,min = (fc,max - fIF) / (fc,min - fIF)
52
I/Q detection advantages
- swap for positive vs negative frequencies
53
Q _______ I if fRF < fLO
Q _______ I if fRF > fLO
leads; lags
54
DSB-SC advantage:
high efficiency
-carrier power is suppressed
55
DSB-SC disadvantage:
complexity
- modulator must suppress carrier
- demodulator must recover signal with carrier
56
LSB stands for?
lower side band
57
USB stands for?
upper side band
58
for DSB-SC, how do you get the plot of only the recovered message signal?
a low pass filter
59
can envelop detection be used for DSB-SC? Under what conditions would it work/not work?
No. There is no constraint on modulation index for DSB-SC. Overmodulation will occur and distort the envelope; no longer representing baseband modulation
60
Can simple envelope detection be used for SSB?
Yes. Suppressing a sideband, does not mean suppressed carrier.
61
Under what conditions will envelope detection be used for SSB?
The carrier must be present
62
Difference between QAM and QPSK?
QAM separately AM modulates I vs Q
QPSK phase modulates I and Q, with one bit on I, the other bit on Q (2 bits sent at a time)
63
Serial vs Parallel Data Bus
Faster? Parallel
More interfaces? Parallel
Greater risk of one bit leaking into another? Parallel (crosstalk)
How to add a bit? Serial, edit the statement Parallel, add another line
64
what does PCM stand for?
pulse code modulation
65
Pros/Cons of PCM
Minimizing wire; Overhead
66
PCM Types
Unipolar NRZ, Bipolar NRZ, Unipolar RZ, Bipolar RZ, Manchester
(NRZ: non return to zero, RZ: return to zero)
67
Manchester encoding
has an implied clock, more robust
68
RS-232
69
What does DSSS stand for?
Direct Sequence Spread Spectrum
70
Matched filter
matches transmit signal and maximizes SNR
- pass max signal
- pass min noise
71
How is a fourier transform a set of matched filters?
complex signal with multiple freqs, well see a peak in that area
- when our guessed signal matches our input signal = get a peak
72
Barker Codes have max length of _____ and min sidelobe of _____
13; 1
73
what allows freq re-use
spatial separation, polarization separation, TDMA, and orthogonal waveforms
73
DSSS
- narrowband signal spread over much wider band
- narrowband signal modulated at high data rate
- result signal is wideband with low power density
74
Achieve high thruput
more orthogonal degrees of freedom enable more capacity, each degree of freedom imposes constraints, constraints add to system complexity and reduce flexibility
75
Central Limit thm
Gaussian curve
76
what does WSS stand for?
wide sense stationary process
77
what does PSD stand for?
power spectral density
78
for PSD and WSS
the mean and variance are time-independent
79
PSD describes
power distribution with respect to frequency
80
sample pdfs
(pic on phone)
81
delta function between two limits
error function erf(x)
82
Q function is
the right tail of the PDF
83
complementary error function erfc(x)
both tails of the pdf
84
erfc(x) formula
= 1- erf(x)
85
AWGN stand for what
additive white gaussian noise
86
PDF, CDF, and Q functions are most useful for
calculating probabilities
87
88
Spatial separation
allows frequency re-use
- ex: wifi (can see neighbors wifi but not out of SLO)
89
what allows frequency re-use
Polarization separation
TDMA
Orthogonal Waveforms (has to be completely 90 degrees)
90
achieving high thruput observations
more orthogonal degrees of freedom enable more capacity (thruput)
91
each degree of freedom _________
imposes constraints
ex: freq accuracy, guard bands, polarization accuracy, timing accuracy
92
constraints add _________ and reduce ________
to system complexity; flexibility
93
Central limit thm
all the world's Gaussian, and all constituents merely add up to noise
(gaussian plot/bead thing)
94
WSS
wide sense stationary process
95
in WSS and PSD, mean and variance are
time-independent
96
in WSS and PSD, autocovariance depends only on
lag between t1 and t2
97
Power Spectral Density describes ___________
power distribution with respect to frequency
98
sample PDFs
(on iphone)
99
what is erf(x)?
error function
- the delta function between two limits
100
what is the Q function?
the right tail of the PDF
101
what is erfc(x)?
complementary error function
erfc = 1 - erf
- area under the two tails of zero mean Gaussian PDF
102
Noise is modeled as AWGN (what is AWGN?)
additive white Gaussian noise
- present in all freqs
-
103
PDF, CDF, and Q functions are most useful for __________
calculating probabilities
104
FSK
frequency domain (phase modulation)
105
BPSK
time domain (phase modulation)
106
Graphs of BPSK, QPSK, 8- 16- 64- ary
on ipad
107
high order modulation is limited by ______
SNR
108
Shannon's Law
C = Blog2(1+SNR)
C: capacity
B: bandwidth
SNR: signal to noise ratio
109
for Shannon's law, high bandwidth means high _________
data through
110
log2(M) =
log10(M)/log10(2)
111
higher data rates require
higher SNR's
112
constraints of BER
- no weather margin
- no implementation margin
- JPL typical 2 dB
113
OFDMA
- orthogonal freq division multiplexing
- data is spread across all carriers or channels
- based on idea that we can have ortho freqs
- dont need a guard band
114
what is special about OFDMA?
robust/immune to fading & multipath (time delay)
115
DSSS
- discrete spread spectrum signal
- low data rate signal spread over wide-band
- inverse to get og signal
116
negative about DSSS
- a lot of bandwidth to spread low data
117
advantages about DSSS
send signals at lower power
- doesn't require exquisite timing alignment of TDMA
- not susceptible frequency effects of FDMA
- guard band
118
CDMA
- code division multiple access
- spread spectrum techniques like DSSS
- choose orthogonal codes to spread data
119
codes are orthogonal when ______
dot product is zero
120
how to maximize capacity?
maximize SNR or maximize bandwidth or BOTH
121
free space path loss eqn
Lp = (4piR/lambda)^2
122
FSK requires _______ _____ than BPSK to achieve the same BER
greater SNR
123
coherent reception will have ______ signal level than non-coherent
greater
- FSK coherent BER curve is lower than FSK non-coherent
124
DPSK is _____
non-coherent
125
DPSK performs a little _____ than coherent BPSK
worse
- DPSK curve will be a little higher than BPSK
126
QPSK sends _______ at the _____
two bits; same time
- each bit gets half the power
127
QPSK has ___ energy per bit as BPSK
same
128
QPSK and QAM are ______
the same thing
129
advantage of QPSK over BPSK?
QPSK allows you to double the data rate
130
maximizing receiver output SNR in AWGN
leads to minimizing detection error probability
131
error probability depends on
noise probability density function
132
what does BER stand for
bit error rate
133
mega
10^6
134
log(10)
1 dB
135
10log(10)
10 dB
136
10log(2)
3 dB
137
10log(4)
6 dB
138
10log(100)
20 dB
139
10log(1000)
30 dB
140
10log(10000)
40 dB
