mini project communication link simulation digital modulation techniques lecture

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Mini Project – Communication Link Simulation Digital Modulation TechniquesDigital Modulation Techniques

Author: University of HertfordshireDate created:Date revised: 2009

AbstractThe following resources come from the 2009/10 BEng (Hons) in Digital Communications & Electronics (course number 2ELE0064) from the University of Hertfordshire. All the mini projects are designed as level two modules of the undergraduate programmes. The objective of this module is to have built communication links using existing AM modulation, PSK modulation and demodulation blocks, constructed AM modulators and constructed PSK modulators using operational function blocks based on their mathematical expressions, and conducted simulations of the links and modulators, all in Simulink®.

Use Matlab®/ Simulink® to design a communication link for AM audio broadcasting. The message signal is a mono audio signal although you may not be able to transmit the full audio frequency range that is normally required for high quality sound.

In addition to the resources found below there are supporting documents which should be used in combination with this resource. Please see:Mini Projects - Introductory presentation. Mini Projects - E-Log.Mini Projects - Staff & Student Guide.Mini Projects - Standard Grading Criteria.Mini Projects - Reflection.

You will also need the ‘Mini Project- Communication Link Simulation’ text file and the lecture presentation on ‘Channels and Noise’.

© University of Hertfordshire 2009 This work is licensed under a Creative Commons Attribution 2.0 License.

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ContentsContents Digital Bandpass ModulationDigital Bandpass Modulation ModulationModulation Types of modulationTypes of modulation Digital ModulationDigital Modulation Digital Modulation – CarrierDigital Modulation – Carrier Four main modulation techniquesFour main modulation techniques Amplitude Shift Keying (ASK)Amplitude Shift Keying (ASK) Frequency Shift Keying (FSK)Frequency Shift Keying (FSK) Phase Shift Keying (PSK)Phase Shift Keying (PSK) PSK: Phasor or vector diagrams (constellation diagram)PSK: Phasor or vector diagrams (constellation diagram) BPSK: Phasor or vector diagram (constellation diagram)BPSK: Phasor or vector diagram (constellation diagram) Quadrature Phase Shift Keying (QPSK) - Phasor or vector d...Quadrature Phase Shift Keying (QPSK) - Phasor or vector d... M-ary Phase Shift Keying (MPSK) - Phasor or vector diagramM-ary Phase Shift Keying (MPSK) - Phasor or vector diagram PSK – General ExpressionPSK – General Expression QPSK – Implementation QPSK – Implementation Reliability & EfficiencyReliability & Efficiency Spectral efficiency and transmitted power trade-offSpectral efficiency and transmitted power trade-off Quadrature Amplitude Modulation (QAM)Quadrature Amplitude Modulation (QAM) Reading listReading list CreditsCredits

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Digital Bandpass ModulationDigital Bandpass Modulation Digital modulation techniquesDigital modulation techniques

• Amplitude Shift Keying (ASK)Amplitude Shift Keying (ASK)• Frequency Shift Keying (FSK)Frequency Shift Keying (FSK)• Phase Shift Keying (BPSK, QPSK)Phase Shift Keying (BPSK, QPSK)• Quadrature Amplitude Modulation (QAM)Quadrature Amplitude Modulation (QAM)

Comparison with regards to:Comparison with regards to:• Reliability (power), Efficiency (bandwidth)Reliability (power), Efficiency (bandwidth)

44

ModulationModulation

What is modulation?What is modulation?

Modulation is the process by which Modulation is the process by which message signals are transformed into message signals are transformed into higher frequency waveforms that are higher frequency waveforms that are compatible with the characteristics of compatible with the characteristics of the channelthe channel

55

Why modulate?Why modulate?

Message signals need to be matched to Message signals need to be matched to the characteristics of channelsthe characteristics of channels

Subsequent advantages of modulation:Subsequent advantages of modulation:• Enables efficient economic communication Enables efficient economic communication

methods to be used as the sharing of methods to be used as the sharing of communication resources is made possible communication resources is made possible (signals can be combined using frequency (signals can be combined using frequency division multiplexing - FDM)division multiplexing - FDM)

• Efficient antennas of reasonable physical size Efficient antennas of reasonable physical size to be constructed for radio communication to be constructed for radio communication systemssystems

66

Types of modulationTypes of modulation

A n a lo gu e M od u la tion D ig ita l M o du la tion

M o d u la tion

Modulation Modulation techniques for techniques for

analogue signalsanalogue signals

Modulation Modulation techniques for techniques for digital signalsdigital signals

77

Digital ModulationDigital Modulation Digital modulation is the process by Digital modulation is the process by

which digital symbols are transformed which digital symbols are transformed into waveforms that are compatible into waveforms that are compatible with the characteristics of the channelwith the characteristics of the channel

To carry out digital modulation, we To carry out digital modulation, we need:need:• A digital A digital messagemessage or or informationinformation or or

modulatingmodulating signal, and signal, and• A sinusoid A sinusoid carrier wavecarrier wave or simply a or simply a

carriercarrierN.B.: The carrier is always of much higher N.B.: The carrier is always of much higher

frequency than the modulating signalfrequency than the modulating signal

88

Digital Modulation - CarrierDigital Modulation - CarrierGeneral form of the carrier wave isGeneral form of the carrier wave is

wherewhere

AAcc = amplitude in volts (V) = amplitude in volts (V)

cc = angular or radian frequency in rads = angular or radian frequency in rads-1-1

cc = phase in radian (rad) = phase in radian (rad)

Alternatively, since Alternatively, since

where where ffcc = frequency in hertz (Hz) = frequency in hertz (Hz)

)cos()( ccc tAtc

)2cos()( ccc tfAtc f 2

99

Digital Modulation - CarrierDigital Modulation - Carrier)2cos()cos()( cccccc tfAtAtc

seconds 1

carrier, theof period Thec

c fT

+A

-A

Tc

t

c(t)

In digital modulation, one of the properties of the In digital modulation, one of the properties of the carrier (amplitude, frequency or phase) is changed carrier (amplitude, frequency or phase) is changed according to the modulating (or information or according to the modulating (or information or message) signalmessage) signal

1010

Four main modulation techniquesFour main modulation techniques

Am plitudeShift Keying

ASK

FrequencyShift Keying

FSK

PhaseShift Keying

PSK

Q uadratureAm plitude

M odula tion (Q AM )

D ig ital M odu la tion

Changing Changing amplitude amplitude

(A(Acc) of carrier ) of carrier according to according to modulating modulating

signalsignal

Changing Changing phase (phase (cc) of ) of

carrier carrier according to according to modulating modulating

signalsignal

Changing Changing frequency frequency

(f(fcc) of carrier ) of carrier according to according to modulating modulating

signalsignal

Combination Combination of ASK and of ASK and

PSKPSK

1111

Amplitude Shift Keying (ASK)Amplitude Shift Keying (ASK)

m(t): modulating signal (baseband signal)m(t): modulating signal (baseband signal)

c(t): carrier wave (high frequency cosine)c(t): carrier wave (high frequency cosine)

y(t): modulated signal – ASK signal y(t): modulated signal – ASK signal (bandpass signal)(bandpass signal)

m(t)m(t) y(t)y(t)

c(t)c(t)

)()()( tctmty

ASK modulator can be ASK modulator can be represented by the represented by the schematic diagram on schematic diagram on the rightthe right

ASK ASK amplitude of carrier is changed amplitude of carrier is changed according to the modulating signalaccording to the modulating signal

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Amplitude Shift Keying (ASK) ctd…Amplitude Shift Keying (ASK) ctd…Binary ASK also called on-off keying (OOK)Binary ASK also called on-off keying (OOK)

11 00 00 11 00 11 11 00Information Information or message or message or baseband or baseband

data data

Carrier wave Carrier wave or carrieror carrier

Data stream:Data stream:

OOK waveform OOK waveform (bandpass (bandpass

signal)signal)

1313

Frequency Shift Keying (FSK)Frequency Shift Keying (FSK)

FSK FSK frequency of carrier is changed frequency of carrier is changed according to modulating signalaccording to modulating signal

Binary FSK (BFSK) represents ones and Binary FSK (BFSK) represents ones and zeros by carrier pulses of two distinct zeros by carrier pulses of two distinct frequencies, ffrequencies, f11 and f and f22

Binary zero Binary zero frequency f frequency f11

Binary one Binary one frequency f frequency f22

1414

Frequency Shift Keying (FSK) ctd…Frequency Shift Keying (FSK) ctd…


data data



BFSK waveform BFSK waveform (bandpass (bandpass

signal)signal)

1515

Frequency Shift Keying (FSK) ctd…Frequency Shift Keying (FSK) ctd…BFSK signal can be BFSK signal can be considered as the considered as the combination of two OOK combination of two OOK signals:signals:

1)1) One representing the One representing the baseband data stream baseband data stream {m(t)}modulated onto a {m(t)}modulated onto a carrier with frequency fcarrier with frequency f11, , andand

2)2) One representing the One representing the inverse data stream inverse data stream {m’(t)} modulated onto a {m’(t)} modulated onto a carrier with frequency fcarrier with frequency f22

cc11(t)=A cos(2(t)=A cos(2ff11t)t)

cc22(t)=A cos(2(t)=A cos(2ff22t)t)

BFSK BFSK signalsignal

m(t)m(t)

m’(t)m’(t)

Schematic of BFSK Schematic of BFSK modulator: as the modulator: as the combination of two OOK combination of two OOK signalssignals

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Phase Shift Keying (PSK)Phase Shift Keying (PSK)PSK PSK phase of carrier is changed phase of carrier is changed

according to modulating signalaccording to modulating signal

)2cos()( ccc tfAtc

+A

-A

Tc

t

c(t)

One period,Tc

Equivalent to a complete turn phase angle

1 complete turn phase angle = 2 rad (=360)

1717

Phase Shift Keying (PSK) ctd…Phase Shift Keying (PSK) ctd…c= 0 rad (=0)

c= rad (=180)

t

t

c(t)

c(t+ )

t

t

c= 3/2 rad (=270)

c= /2 rad (=90)

c(t+ 3/2)

c(t+ /2)

1818

Phase Shift Keying (PSK) ctd…Phase Shift Keying (PSK) ctd…

)2cos()( ccc tfAtc

Binary PSK (BPSK) represents ones and Binary PSK (BPSK) represents ones and zeros by shifting the phase by zeros by shifting the phase by 11 and and 22

Binary zero Binary zero phase phase 1 1 (0 rad or 0(0 rad or 0))

Binary one Binary one phase phase 2 2 (( rad or 180 rad or 180))

PSK PSK phase of carrier is changed phase of carrier is changed according to modulating signalaccording to modulating signal

1919

Phase Shift Keying (PSK) ctd…Phase Shift Keying (PSK) ctd…


data data



BPSK waveform BPSK waveform (bandpass (bandpass

signal)signal)

2020

PSK: Phasor or vector diagrams PSK: Phasor or vector diagrams (constellation diagram)(constellation diagram)

=0 rad =0

= 2 rad =360

=/2 rad

=90

= rad

=180

=3/2 rad

=270

2121

BPSK: Phasor or vector diagram BPSK: Phasor or vector diagram (constellation diagram)(constellation diagram)

=0

=/2

=

=3/2

m1m2

Binary: two possible states mBinary: two possible states m11 and m and m22

Decision region 1Decision region 1Decision region 2Decision region 2

Decision boundaryDecision boundary

Euclidean Euclidean distance: distance distance: distance between two between two message pointsmessage points

2222

Quadrature Phase Shift Keying Quadrature Phase Shift Keying (QPSK) - Phasor or vector diagram(QPSK) - Phasor or vector diagram

=0

=/2

=

=3/2

m1

m2

Quadrature: four possible states mQuadrature: four possible states m11, m, m22,m,m33 and m and m44

m4

m3

Decision region 1Decision region 1






2323

M-ary Phase Shift Keying (MPSK) - M-ary Phase Shift Keying (MPSK) - Phasor or vector diagramPhasor or vector diagram

=0

=/2

=

=3/2

m1

m3

M-ary: M possible states mM-ary: M possible states m11, m, m22, m, m33, … m, … mMM

m7

m5

m8m6

m4 m2

Region 1Region 1

Region 8Region 8

Region 4Region 4Region 2Region 2

Region 7Region 7

Region 3Region 3

Region 5Region 5

Region 6Region 6

Signal Signal constellation constellation

for 8-PSKfor 8-PSK

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PSK – General ExpressionPSK – General Expression The general analytic expression of PSK is more The general analytic expression of PSK is more

popularly written as popularly written as

E is the symbol energy and T is the information signal’s symbol E is the symbol energy and T is the information signal’s symbol time duration. i=1, 2, ..M. time duration. i=1, 2, ..M.

Phase term Phase term ii(t)(t) has M discrete values given byhas M discrete values given by

BPSK, M=2; QPSK, M=4; 8-PSK, M=8; etc BPSK, M=2; QPSK, M=4; 8-PSK, M=8; etc

M

it

ttT

Etm

i

ici

2)(

)(cos2

)(

2525

PSK – CodingPSK – Coding BPSK: each state (m1, m2) is BPSK: each state (m1, m2) is

represented by one digit (0, 1)represented by one digit (0, 1) QPSK: each state (m1, m2, m3, m4) QPSK: each state (m1, m2, m3, m4)

is represented by two digits (00, 01, is represented by two digits (00, 01, 10, 11)10, 11)

8PSK: each state is presented by 8PSK: each state is presented by three digits (000, 001, 010, 011, 100, three digits (000, 001, 010, 011, 100, 101, 110, 111) 101, 110, 111)

Etc… Etc…

2626

QPSK – Implementation QPSK – Implementation By expanding the general expression, QPSK can be By expanding the general expression, QPSK can be

implemented in the following way. implemented in the following way. In QPSK the information bit stream is divided to form In QPSK the information bit stream is divided to form

two streams, in-phase (I) and in quadrature (Q), two streams, in-phase (I) and in quadrature (Q), comprising of the even and odd bits of the original comprising of the even and odd bits of the original information signal respectivelyinformation signal respectively

Since each transmitted symbol is represented by two Since each transmitted symbol is represented by two successive binary pulses, the symbol rate of the I and successive binary pulses, the symbol rate of the I and Q waveforms is half the bit rate of the information Q waveforms is half the bit rate of the information signal (signal (Rs=RbRs=Rb/log/log22M).M).

Subsequently the bipolar I and Q streams are used to Subsequently the bipolar I and Q streams are used to modulate the components of a carrier frequency in modulate the components of a carrier frequency in quadraturequadrature• Modulation of each orthogonal carrier follows a DSB-SC-AM Modulation of each orthogonal carrier follows a DSB-SC-AM

mode resulting in two BPSK signalsmode resulting in two BPSK signals

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QPSK Circuit DiagramQPSK Circuit Diagram Two carriers are inphase quadrature. Two carriers are inphase quadrature. In the case of the inphase data stream, the phase of the cosine In the case of the inphase data stream, the phase of the cosine

carrier is shifted, at symbol transitions, between 0carrier is shifted, at symbol transitions, between 0oo and 180 and 180oo

Equivalently the quadrature data stream shifts the phase of the sine Equivalently the quadrature data stream shifts the phase of the sine function between 90function between 90oo and 270 and 270oo

The modulated signals are combined linearly to produce the QPSK The modulated signals are combined linearly to produce the QPSK waveform waveform θθ(t)=(t)=00oo, 90, 90oo, 180, 180oo and 270 and 270oo

2828

Reliability & EfficiencyReliability & Efficiency

Reliability of scheme: how likely are Reliability of scheme: how likely are errors; this is related to the Euclidean errors; this is related to the Euclidean distancedistanceExpressed by the BER versus SNR Expressed by the BER versus SNR (Eb/No): What is the probability of (Eb/No): What is the probability of error?error?

Efficiency: measure of the data rateEfficiency: measure of the data rateExpressed by the number of bits per Expressed by the number of bits per symbolsymbol

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Reliability & Efficiency ctd…Reliability & Efficiency ctd…

As M increases, the Euclidean As M increases, the Euclidean distance decreasesdistance decreasesHence, the probability of error Hence, the probability of error increases; therefore the reliability increases; therefore the reliability decreasesdecreases

As M increases, data rate increasesAs M increases, data rate increasesHence the efficiency increasesHence the efficiency increases

Trade-off between reliability and Trade-off between reliability and efficiency to be consideredefficiency to be considered

3030

Spectral efficiency and Spectral efficiency and transmitted power trade-offtransmitted power trade-off

For the same system bandwidth a For the same system bandwidth a quadrature modulation scheme can quadrature modulation scheme can transmit twice the data rate achievable transmit twice the data rate achievable with its binary counterpartwith its binary counterpart

The superior performance of The superior performance of MM-level -level signaling by means of higher achievable signaling by means of higher achievable transmission rates for a given channel transmission rates for a given channel bandwidth is achieved in the expense of bandwidth is achieved in the expense of increased transmitted power (better SNR) increased transmitted power (better SNR) for a required reliability (BER). for a required reliability (BER).

3131

Quadrature Amplitude Modulation Quadrature Amplitude Modulation (QAM)(QAM)

Also known as Amplitude Phase Also known as Amplitude Phase Keying (APK)Keying (APK)

Combination of ASK and PSKCombination of ASK and PSK 8-QAM8-QAM 16-QAM16-QAM

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Reading listReading list

Sklar, B., (2001), “Digital Sklar, B., (2001), “Digital Communications: Fundamentals and Communications: Fundamentals and Applications”, Prentice Hall, 2Applications”, Prentice Hall, 2ndnd Edition: sections 4.1 – 4.2Edition: sections 4.1 – 4.2

Glover, I.A & Grant P.M., (2004), Glover, I.A & Grant P.M., (2004), Digital Communications”, Pearson Digital Communications”, Pearson Prentice Hall, 2Prentice Hall, 2ndnd Edition: sections Edition: sections 11.1 – 11.311.1 – 11.3

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