learning outcome
DESCRIPTION
EEC4113 Data Communication & Multimedia System Chapter 3: Broadband Encoding by Muhazam Mustapha, July 2010. Learning Outcome. By the end of this chapter, students are expected to be able to explain link level broadband encoding for transmission. Chapter Content. Amplitude Shift Keying - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/1.jpg)
EEC4113Data Communication &
Multimedia SystemChapter 3: Broadband Encoding
by Muhazam Mustapha, July 2010
![Page 2: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/2.jpg)
Learning Outcome
• By the end of this chapter, students are expected to be able to explain link level broadband encoding for transmission
![Page 3: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/3.jpg)
Chapter Content
• Amplitude Shift Keying
• Frequency Shift Keying
• Phase Shift Keying
• Pulse Width Modulation
• Quadrature Modulation
• Spread Spectrum Technology
![Page 4: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/4.jpg)
Amplitude Shift Keying
![Page 5: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/5.jpg)
Amplitude Shift Keying (ASK)
• Values represented by different amplitudes of carrier frequency
• It is similar to Amplitude Modulation (AM) in analog communication, but with only two levels of amplitude
• Usually, one amplitude is zero – i.e. presence and absence of carrier
![Page 6: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/6.jpg)
Amplitude Shift Keying (ASK)
• Susceptible to sudden changes in gain
• Up to 1200bps on voice grade lines
• Used over optical fiber
![Page 7: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/7.jpg)
Amplitude Shift Keying (ASK)
0 0 1 1 0 1 0 0 0 1 0
0binary
1binary
0
)2sin()(
tfA
ts c
![Page 8: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/8.jpg)
Frequency Shift Keying
![Page 9: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/9.jpg)
Frequency Shift Keying (FSK)
• Different frequency used to represent data
• Two types:– Binary FSK (BFSK)– Multiple FSK (MFSK)
![Page 10: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/10.jpg)
FSK on Voice Grade Line
Signal strength
Frequency (Hz)1170 2125
Spectrum of signal transmitted in one direction Spectrum of signal
transmitted in opposite direction
Full Duplex FSK Transmission on a Voice Grade Line
![Page 11: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/11.jpg)
Multiple FSK
• More than two frequencies used
• Each signaling element represents more than one bit– Example: 3 bits per signal element, 8 signal
elements, 8 different frequencies
• Advantage: More bandwidth efficient
• Disadvantage: More prone to error
![Page 12: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/12.jpg)
Binary Frequency Shift Keying (BFSK)
• Most common form of FSK
• Two binary values are represented by two different frequencies
• It is similar to Frequency Modulation (FM) in analog communication, but with only two frequencies
• Less susceptible to error than ASK
![Page 13: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/13.jpg)
Binary Frequency Shift Keying (BFSK)
• Up to 1200bps on voice grade lines
• High frequency radio transmission (3 to 30 MHz)
• Even higher frequency on LANs using coaxial cable
![Page 14: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/14.jpg)
Binary Frequency Shift Keying (BFSK)
0 0 1 1 0 1 0 0 0 1 0
0binary
1binary
)2sin(
)2sin()(
2
1
tfA
tfAts
![Page 15: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/15.jpg)
Phase Shift Keying
![Page 16: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/16.jpg)
Phase Shift Keying (PSK)
• Phase of carrier signal is shifted to represent data
FSK PSKASK
QAM
Broadband signaling
![Page 17: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/17.jpg)
Binary Phase Shift Keying (BPSK)
0 0 1 1 0 1 0 0 0 1 0
0binary
1binary
)2sin(
)2sin()(
tfA
tfAts
c
c
• Two phases represent two binary digits
![Page 18: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/18.jpg)
Differential Phase Shift Keying (DPSK)
0 0 1 1 0 1 0 0 0 1 0
• Binary 1: Phase change
• Binary 0: No phase change
![Page 19: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/19.jpg)
Pulse Width Modulation
![Page 20: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/20.jpg)
Pulse Width Modulation (PWM)
• The width (duration) of the pulse is used to represent data
• In analog communication, PWM needs continuous width values to represent the analog waveform at certain sampling instances
• In data (digital) communication, the pulses can have discrete values of width
![Page 21: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/21.jpg)
Pulse Width Modulation (PWM)
• An integrator or timing circuit can be used to decode the carried bits
10 01 11 01 00Data
Pulse
![Page 22: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/22.jpg)
Quadrature Modulation
![Page 23: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/23.jpg)
Quadrature PSK (QPSK)• More efficient use by each signal representing
more than one bit– e.g. for shifts of π/2 (90°), each element represents two
bits
10 4
2sin
00 4
32sin
01 4
32sin
11 4
2sin
)(
c
c
c
c
fA
fA
fA
fA
ts
135°:01 45°:11
315°:10
Constellation diagram for QPSK
225°:00
![Page 24: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/24.jpg)
Quadrature PSK (QPSK)• Alternative choice of phases:
270°:11
Constellation diagram
90°:01
180°:10 0°:00
Dibit Phase
00 0
01 90
10 180
11 270
![Page 25: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/25.jpg)
00 11 01 00 10
Quadrature PSK (QPSK)
![Page 26: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/26.jpg)
Phase Detector
Ref
Ref
Ref
Ref
Signal
Signal
Signal
Signal
phase leading
phase lagging
phase lagging
phase lagging
phase lagging
phase leading
phase leading
phase leading
![Page 27: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/27.jpg)
QPSK and OQPSK Modulators• Offset QPSK (orthogonal QPSK)
– Delay in Q stream
π/2
Σ2 bit
serial to parallelconversion
DelayTb
binary input
bTR
1
R/2 bps
R/2 bps
I(t)an = ±1
Q(t)bn = ±1
carrier
frequency
phase shift
output
s(n)
OQPSK only
![Page 28: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/28.jpg)
1 3 5 7 9
Examples: QPSK & OQPSK Waveforms
2 4 6 8 10bit number
1 1 −1 −1 1−1 1 −1 1 1value
I I I I IQ Q Q Q Q
input signal
I(t)
Q(t)
1
2
3
4
5
6
7
8
9
10
phase of output signal −π/4 π/4 −3π/4 3π/4 π/4
Q(t−Tb)
phase of output signal −π/4 π/4 −3π/4 3π/4 π/4−π/4 3π/4 −3π/4 π/4
![Page 29: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/29.jpg)
OQPSK
• QPSK sometimes causes a phase change of 180° (π).
• Phase change of 180° sometimes means discontinuity jump, and it is the largest possible jump.
• The jump causes a large amplitude of high frequency and small amplitude of low frequency in transmission, and if it is low pass filtered, then the signal will experience a large fluctuation during the phase change.
![Page 30: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/30.jpg)
OQPSK
• OQPSK was designed to reduce this fluctuation by delaying one of the signal combined in the modulator.
• Revisit the example: Transition between bit 3-4 & 5-6 causes 180° in QPSK, but OQPSK signal made a gradual 2 steps of 90°. This reduces the fluctuation.
• The signal would be strobed at the right time to get the right binary combination.
![Page 31: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/31.jpg)
input signal
I(t)
Q(t)
1
2
3
4
5
6
7
8
9
10
phase of output signal −π/4 π/4 −3π/4 3π/4 π/4
Q(t−Tb)
phase of output signal −π/4 π/4 −3π/4 3π/4 π/4−π/4 3π/4 −3π/4 π/4
180° transition
two 90° transitions
OQPSK
![Page 32: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/32.jpg)
Multilevel PSK• More levels taking more than 2 bits at a time
– e.g. Transmit 3 bits at a time by using 8 phase angles (8-PSK)
– Further, each angle can have more than one amplitude (QAM)
Constellation diagram
010Tribit Phase
000 0
001 45
010 90
011 135
100 180
101 225
110 270
111 315
011
100
101
110
111
000
001
![Page 33: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/33.jpg)
Quadrature Amplitude Modulation (QAM)• QAM used on Asymmetric Digital Subscriber Line
(ADSL) and some wireless standards• Combination of ASK and PSK• Logical extension of QPSK• Send different signals simultaneously on same
carrier frequency– Signals are distinguished by phase and amplitude
difference
![Page 34: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/34.jpg)
QAM Constellations
010
011
100101
110
111
000 001
01
10 11
00
4-QAM1 amplitude 4 phases
8-QAM2 amplitudes 4
phases
![Page 35: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/35.jpg)
QAM Constellations
3 amplitudes 12 phases
16-QAM
16-QAM
4 amplitudes 8 phases2 amplitudes 8 phases
16-QAM
Standard 9600 bps modem use 12 angles, four of which have twoamplitudes for a total of 16 different signal elements
![Page 36: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/36.jpg)
Spread Spectrum Technology
![Page 37: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/37.jpg)
Spread Spectrum Technology
• Spread spectrum technology is a method whereby a signal is being transmitted over a bandwidth much wider than the required bandwidth to transmit the intended information.
• The main reason for the technology is security.– The signal that has been scattered over a large
bandwidth can easily be scrambled and become hard to detect or interpret
![Page 38: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/38.jpg)
Frequency Hopping Spread Spectrum (FHSS)
• The communication is done over many carrier frequencies that is changed randomly
• Sequence:– Initiating side sends a request via a predefined
frequency– The receiving side sends a number, known as seed– The initiating side uses the number to calculate a
sequence of frequencies to be used– The initiating side sends a synchronization signal
through the first frequency in the sequence– Both sides would then continue communication via
those frequencies at known timing
![Page 39: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/39.jpg)
Signal strength
Frequency (Hz)
Frequency Hopping Spread Spectrum (FHSS)
Carrier frequency hops from channel to channel
![Page 40: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/40.jpg)
Carrier Frequency
Time
Frequency Hopping Spread Spectrum (FHSS) Carrier frequencies are
chosen at random over times
1
2
3
4
5
6
7
8
1 2 3 4 5 6 7 8 9 10 11 12 13 14
![Page 41: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/41.jpg)
Direct Sequence Spread Spectrum (DSSS)
• The communication is done over many phase modulations that is applied randomly
• The original modulated signal is further phase modulated at random phases – called chips– The rate of chips are much higher than the data rate
• The receiver should know the same sequence of chips– The original data can then be retrieved by removing the
chips
![Page 42: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/42.jpg)
Signal strength
Frequency (Hz)
Narrow Band Spectrum
Spread Spectrum
Noise Level
Direct Sequence Spread Spectrum (DSSS)
![Page 43: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/43.jpg)
Other Spread Spectrum Technologies
• Time Hopping Spread Spectrum (THSS)– Data is burst at random times
Time
bursts
![Page 44: Learning Outcome](https://reader035.vdocument.in/reader035/viewer/2022070401/568136ab550346895d9e515d/html5/thumbnails/44.jpg)
Other Spread Spectrum Technologies
• Chirp Spread Spectrum (CSS)– A chirp is sinusoidal signal that increases or decreases
over some period of time– CSS data is transmitted over a pulse that is modulated
by chirp (time varying carrier frequency)
Frequency (Hz)
data spectrum at start of pulse
data spectrum at end of pulse