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TM355 > Block 1 Part 2 > Flashcards

Block 1 Part 2 Flashcards

1
Q

Carrier waves (b-r-s)

A
  • basic radio waves that are sinusoidal
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2
Q

time domain representation (h-s-s-v-t)

A
  • how strength of signal varies over time
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3
Q

Frequency domain representation (s-l-f-p-a)

A
  • single spike or line placed at its frequency with peak amplitude
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4
Q

Discrete spectrum (a-p-s-t), (s-r-l-s-f)

A
  • all periodic signals have this

- means spectrum can be represented by line or series of lines at specific frequencies

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5
Q

harmonic (f-c-p-s-m-h-f-f)

A
  • each frequency component of periodic signal is a multiple, known as harmonic, of fundamental frequency f
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6
Q

Fourier series (s-c-j-t-f-f)

A

series of components that join together to fundamental frequency

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7
Q

Three basic modulation schemes

A
  • Amplitude-shift keying (ASK)
  • Frequency-shift keying (FSK)
  • Phase-shift keying (PSK)
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8
Q

Desirable characteristics of digital modulation schemes (b-e), (p-e), (p-w-m-f-c), (c-e-s-I)

A
  • bandwidth efficient
  • power efficient
  • performs well in multipath fading channels
  • cost effective and simple to implement
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9
Q

Fourier transform (f-d-r-n-p-s)

A
  • gives frequency domain representation of non-periodic signals
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10
Q

Non-periodic signals (s-c-c-s, c-d-f-c)

A
  • have spectra comprising a continuous spectrum, means continuous distribution of frequency components
    pg 104
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11
Q

Three basic digital modulation schemes

A
  • amplitude-shift keying (ASK)
  • frequency-shift keying (FSK)
  • phase-shift keying (PSK)
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12
Q

Desirable qualities when choosing digital modulation scheme

A
  • Bandwidth efficient
  • power efficient
  • performs well in multipath fading channels
  • cost effective and simple to implement
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13
Q

Fourier transform

A
  • gives frequency domain representation of non-periodic signals
  • have spectra comprising a continuous spectrum
  • means continuous distribution of frequency components
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14
Q

Important inverse relationship between time and frequency domains (n-p-b-r), (d-r-I-b-r)

A
  • the narrower the pulse, the broader is spectrum

- as data rate increases, more bandwidth is required

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15
Q

ASK

A
  • special case of AM

- amplitude of carrier signal is modified

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16
Q

On-off keying (OOK) (s-f-a), (b-t-n), (d-a-d-1-0),

A
  • simplest form of ASK
  • either bursts of waves are transmitted or they aren’t
  • this done according to whether input data is 1 or 0
  • other versions of ASK use differing (non-zero) amplitudes to represent 1 and 0
17
Q

Advantages of ASK (s-l-c), (s-a-z-c-g)

A
  • simple and low cost to implement

- switching between amplitudes usually done at zero crossings on graph

18
Q

FSK

A
  • type of frequency modulation
  • frequency of carrier signal that is modified
  • bursts of data transmitted at one frequency or another
19
Q

What is an important parameter of FSK

A
  • the frequency separation between the two sinusoids

- this determines the bandwidth of modulated signal

20
Q

What are advantages of using two frequencies close together in FSK

A
  • reduces the separation of the two signals
  • therefore the overall bandwidth
  • receiver still ahs to be able to distinguish both signals
  • limit to how close signals can be
21
Q

Minimum-shift keying

A
  • specific case of FSK

- uses smallest possible separation between two sinusoids that still works

22
Q

Gaussian minimum-shift keying (GMSK)

A
  • used in second generation mobile cellular system

- special case of MSK that uses gaussian pulse

23
Q

PSK

A
  • most widely use digital modulations scheme
  • in BSPK 0 and 1 represented by segments of sinusoids that differ in their phase
  • normally separated by half a cycle
  • BSPK signal almost as simple to produce as ASK signal but less susceptible to noise
24
Q

Bit error rate (BER)

A
  • defined as number of bits received in error divided by number of bits transmitted
  • low BER desirable
25
Q

Symbols

A
  • different carrier states known as symbols i.e. 1 and 0

- if more than two possible carrier states, then more than two symbols available

26
Q

Baud

A
  • refers to number of symbols per second

- one baud is one symbol per second

27
Q

Two most widely used modulation schemes used in wireless communications

A
  • quadrature phase-shift keying (QPSK)

- quadrature amplitude modulation (QAM)

28
Q

Quadrature phase-shift keying (QPSK)

A

-application of complementary pairs of amplitudes to two simultaneous sinusoidal waves differing in phase by one quarter cycle

29
Q

I and Q waves

A
  • sinusoidal waves (of same frequency) with phase difference of quarter or three quarters of cycle said to be in quadrature phase relationship
  • I wave refers to in phase wave or component of these waves
  • Q wave refers to quadrature wave or component of two waves
30
Q

What can I wave and Q wave be thought of

A
  • I wave also thought of as sine wave

- Q wave also thought of as cosine wave

31
Q

Quadrature relationship

A
  • despite inversion of either or both I and Q waves both wave forms can be modulated using BPSK
  • relationship is preserved between them
32
Q

Orthogonal

A
  • way to describe I and Q waves
  • means signals are transmitted simultaneously
  • one can be fully recovered at receiver without interference from other one
33
Q

QPSK data rate

A
  • can achieve twice the data rate of BSPK for given bandwidth
34
Q

How to increase number of symbols further from QPSK

A
  • amplitude of modulated signal remains fixed but number of different phases carrier wave can take continues to increase
  • or combine QPSK with ASK and introduce more amplitude and phases

TM355 (8 decks)

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