Application of Phase Modulation

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APPLICAT

APPLICATIONS OF

IONS OF PHASE MODULATION

PHASE MODULATION

Abstract

Abstract _{:: An Introductory or initial report}_{An Introductory or initial report}

on the applications of phase modulation, on the applications of phase modulation, the topic of the term paper for the current the topic of the term paper for the current 3

3rdrd_semester._semester.

I. I.

IIII.. IINNTTRROODDUUCCTTIIOON N TTO O TTHHE E TTOOPPIICC

Modulation:-It is defined as the process of alternating some of It is defined as the process of alternating some of the characteristics such as amplitude, frequency or the characteristics such as amplitude, frequency or phase angle of the carrier signal of higher frequency phase angle of the carrier signal of higher frequency in accordance with the low

in accordance with the low frequency modulatingfrequency modulating signal.

signal.

Carrier Carrier

wave:-It is a high frequency constant amplitude and non It is a high frequency constant amplitude and non interrupted wave generated by radio

interrupted wave generated by radio frequencyfrequency oscillator these waveforms are inaudible it

oscillator these waveforms are inaudible it meansmeans we can’t listen these radio

we can’t listen these radio waveforms even throughwaveforms even through loud speakers.

loud speakers.

Need of

modulation:-Need of modulation:- Low frequency signals can’tLow frequency signals can’t be transmitted over long distances if radiated be transmitted over long distances if radiated directly in space because of interference with directly in space because of interference with similar frequency range waveforms . We require similar frequency range waveforms . We require modulation because of following reasons

modulation because of following reasons

1)

Short operating range:-Short operating range:- TheThe energy of any wave depends energy of any wave depends upon its frequency so larger the upon its frequency so larger the frequency of the wave the greater frequency of the wave the greater the energy associated with it. For the energy associated with it. For small signal frequency power is small signal frequency power is lower so it can be transmitted lower so it can be transmitted over large distances.

over large distances.

2)

Poor radiation efficiency:-Poor radiation efficiency:- AtAt audible frequency the radiation audible frequency the radiation efficiency is poor so we require to efficiency is poor so we require to increase the frequency of the increase the frequency of the

wave to be radiated in order to wave to be radiated in order to increase the radiation efficiency. increase the radiation efficiency.

3)

Mutual interference:-Mutual interference:- TheThe frequency of noises such as frequency of noises such as thermal noises and

thermal noises and

electromagnetic noises lies in the electromagnetic noises lies in the range of audible frequency so it range of audible frequency so it can be easily interfered by these can be easily interfered by these noises. When we modulate It over noises. When we modulate It over a carrier signal its frequency a carrier signal its frequency increases and thus it becomes increases and thus it becomes immune to noises.

immune to noises.

4)

Huge antenna requirement:-Huge antenna requirement:-For

For efficient efficient radiation radiation of of signalsignal the length of transmitting and the length of transmitting and receiving antenna should be at receiving antenna should be at least one quarter of the wave least one quarter of the wave length that is

length that is

l=1/4(velocity/ frequency (hz)) l=1/4(velocity/ frequency (hz))

so we see that the length of so we see that the length of the antenna is inversely

the antenna is inversely

proportional to the frequency of proportional to the frequency of modulating signal thus high modulating signal thus high frequency of modulated signal frequency of modulated signal leads to small length of antenna leads to small length of antenna and vice versa.

and vice versa.

Types of Types of

modulation:-Modulation is mainly done in

Modulation is mainly done in three ways:-three

ways:-1)

1)

Amplitude Amplitude modulation(AM)modulation(AM):-:-InIn amplitude modulation the

amplitude modulation the amplitude of the carrier signal is amplitude of the carrier signal is varied in accordance with the varied in accordance with the modulating signal .Example is modulating signal .Example is shown below

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2)

Frequency Modulation (FM):-Frequency Modulation (FM):- InIn frequency modulation the

frequency modulation the frequency of the carrier signal is frequency of the carrier signal is varied in accordance with varied in accordance with modulating signal. Example is modulating signal. Example is shown below

shown below

3)

Phase modulation(PMPhase modulation(PM):- In):- In phase modulation the phase phase modulation the phase angle of the carrier signal is angle of the carrier signal is varied in accordance with the varied in accordance with the modulating signal .The diagram is modulating signal .The diagram is shown below

shown below

Modulating Index Modulating Index

(m):-It is the ratio of the extent by which the amplitude, It is the ratio of the extent by which the amplitude, frequency or phase angle of the carrier wave is frequency or phase angle of the carrier wave is varied to its original amplitude, frequency or phase varied to its original amplitude, frequency or phase angle when the carrier

angle when the carrier waveform is waveform is unmodulated unmodulated .It.It is expressed in percentage.

is expressed in percentage.

Now we come to our main

Now we come to our main topic ”phase modulation”topic ”phase modulation”

The question arises, What is phase

The question arises, What is phase modulation???modulation???

Answer to this is that li

Answer to this is that li ke frequency modulation,ke frequency modulation, phase modulation is also a technique of modulation phase modulation is also a technique of modulation in which information is represented as variation in in which information is represented as variation in the instantaneous phase of the

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It would become

It would become more more clear from the followingclear from the following

example-Let us consider that signal which we want to send is Let us consider that signal which we want to send is represented by s(t) and carrier on which signal is to represented by s(t) and carrier on which signal is to be modulated is represented by

be modulated is represented by

c(t)=A

c(t)=Accsin (ωsin (ωcct +Фt +Фcc))

thus

thus the modulated signal cthe modulated signal comes out to beomes out to be

c(t)=A

c(t)=Accsin (ωsin (ωcct +s(t)+Фt +s(t)+Фcc))

this shows that how the phase of the carrier wave is this shows that how the phase of the carrier wave is modulated according to signal which is to be sent. modulated according to signal which is to be sent.

In phase modulation there are 2 regions of In phase modulation there are 2 regions of particular interest:

particular interest:

1)

For smallFor small amplitudeamplitude signals, PMsignals, PM is similar to

is similar to amplitude modulationamplitude modulation (AM) and exhibits its unfortunate (AM) and exhibits its unfortunate doubling of

doubling of basebandbaseband bandwidthbandwidth and poor efficiency.

and poor efficiency.

2)

For a single largeFor a single large sinusoidalsinusoidal signal, PM is similar to FM, and signal, PM is similar to FM, and its bandwidth is approximately its bandwidth is approximately 2(m+1)f

2(m+1)f mm

where f

where f mm= ω= ωmm/2π and m is the/2π and m is the modulation index.

modulation index.

Phase modulation is similar in practice to

Phase modulation is similar in practice to frequencyfrequency modulation

modulation (FM(FM). When the instantaneous phase of ). When the instantaneous phase of a carrier is varied, the

a carrier is varied, the instantaneous frequencyinstantaneous frequency changes as well. The converse also holds: changes as well. The converse also holds: WhenWhen the instantaneous frequency is varied, the

the instantaneous frequency is varied, the instantaneous phase changes. But PM and FM instantaneous phase changes. But PM and FM areare not exactly equivalent, especially in analog

not exactly equivalent, especially in analog applications. When an FM receiver is used to applications. When an FM receiver is used to demodulate a PM signal, or when an FM signal is demodulate a PM signal, or when an FM signal is intercepted by a receiver designed for PM, the intercepted by a receiver designed for PM, the audio is distorted. This is because the relationship audio is distorted. This is because the relationship between phase and frequency variations is not between phase and frequency variations is not linear; that is, phase and frequency do not vary in linear; that is, phase and frequency do not vary in direct proportion.

direct proportion.

Phase shift or phase Phase shift or phase

shifting:-The phase of a wave is a specific point or The phase of a wave is a specific point or benchmark along that wave. A phase shift benchmark along that wave. A phase shift is anis an observable repositioning of this benchmark observable repositioning of this benchmark

between successive transmissions. A pulse between successive transmissions. A pulse Doppler radar, in its simplest form, provides a Doppler radar, in its simplest form, provides a reference signal by which

reference signal by which

changes in the frequency phase of successively changes in the frequency phase of successively received pulses may be recognized. The known received pulses may be recognized. The known phase of the transmitted signal

phase of the transmitted signal allows measurementallows measurement of

of the the phase phase of of the the received received signal. signal. The The Doppler Doppler shift

shift associated with associated with the echo the echo from which from which thethe return originated is calculated from the time rate of return originated is calculated from the time rate of change of phase. The phase of a wave, measured change of phase. The phase of a wave, measured in degrees, where 360 degrees equals one

in degrees, where 360 degrees equals one wavelength, indicates the current position of the wavelength, indicates the current position of the wave relative to a reference

wave relative to a reference position. For example,position. For example, look at figure 2-18. At time T1 (fig. 2-18, view A), look at figure 2-18. At time T1 (fig. 2-18, view A), the position of the wave along the vertical line was the position of the wave along the vertical line was as shown, while at time T2 (fig. 2-18, view B), the as shown, while at time T2 (fig. 2-18, view B), the position of the wave along the vertical line was as position of the wave along the vertical line was as shown. Notice that the wavelength did not change shown. Notice that the wavelength did not change from T1 to T2. However, the

from T1 to T2. However, the wave’s position relativewave’s position relative to the vertical line changed 1/4 wavelength, or 90 to the vertical line changed 1/4 wavelength, or 90 degrees. This change is the phase shift.

degrees. This change is the phase shift.

Modulation Modulation

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index:-The modulation index of a phase modulated carrier The modulation index of a phase modulated carrier wave is given by

wave is given by

m=Δ m=ΔƟƟ

wh

wherere Δ e Δ is tƟƟis the phe peaeak phk phasasee deviation.

deviation.

Phase shift Phase shift

keying:-it is the digkeying:-ital version of phase modulation. It it is the digital version of phase modulation. It conveys

conveys datadata by changing, or modulating, theby changing, or modulating, the phase

phase of a referenceof a reference signalsignal (the(the carrier wave)carrier wave).. Any digital modulation scheme uses a

Any digital modulation scheme uses a finitefinite number number of distinct signals to represent digital data. PSK of distinct signals to represent digital data. PSK uses a finite number of phases, each assigned a uses a finite number of phases, each assigned a unique pattern of

unique pattern of binarybinary bits.bits. Usually, each phaseUsually, each phase encodes an equal number of bits. Each pattern of encodes an equal number of bits. Each pattern of bits forms the

bits forms the symbolsymbol that is represented by thethat is represented by the particular phase. The

particular phase. The demodulator demodulator , which is, which is

designed specifically for the symbol-set used by the designed specifically for the symbol-set used by the modulator, determines the phase of

modulator, determines the phase of the receivedthe received signal and maps it back

signal and maps it back to the symbol it represents,to the symbol it represents, thus recovering the original data. This requires the thus recovering the original data. This requires the receiver to be able to compare the phase of the receiver to be able to compare the phase of the received signal to a reference signal — such a received signal to a reference signal — such a system is termed coherent (and referred to system is termed coherent (and referred to asas CPSK).

CPSK).

Alternatively, instead of using the bit patterns to set Alternatively, instead of using the bit patterns to set the phase of the wave, it can instead be used to the phase of the wave, it can instead be used to change it by a specified amount. The demodulator change it by a specified amount. The demodulator then determines the changes in the phase of the then determines the changes in the phase of the received signal rather than the phase itself. Since received signal rather than the phase itself. Since this scheme depends on the difference

this scheme depends on the difference betweenbetween successive phases, it is termed differential successive phases, it is termed differential phase-shift keying (DPSK). DPSK can be significantly shift keying (DPSK). DPSK can be significantly simpler to implement than ordinary PSK since there simpler to implement than ordinary PSK since there is no need for the demodulator to have a copy of is no need for the demodulator to have a copy of the reference signal to determine the exact phase of the reference signal to determine the exact phase of the received signal (it is

the received signal (it is a non-coherent scheme). Ina non-coherent scheme). In exchange, it produces more erroneous

exchange, it produces more erroneous

demodulations. The exact requirements of the demodulations. The exact requirements of the particular scenario under consideration determine particular scenario under consideration determine which scheme is used.

which scheme is used.

Binary phase-shift keying Binary phase-shift keying

(BPSK):-BPSK (also sometimes called PRK,

BPSK (also sometimes called PRK, Phase ReversalPhase Reversal Keying, or 2PSK) is the

Keying, or 2PSK) is the simplest form of phase shiftsimplest form of phase shift

keying (PSK). It uses two phases which are keying (PSK). It uses two phases which are separated by 180° and so can also be termed separated by 180° and so can also be termed 2-PSK. It does not particularly matter

PSK. It does not particularly matter exactly whereexactly where the constellation points are positioned, and in this the constellation points are positioned, and in this figure they are shown on the real axis, at 0° and figure they are shown on the real axis, at 0° and 180°. This modulation is the most robust of all the 180°. This modulation is the most robust of all the PSKs since it takes the highest level of noise or PSKs since it takes the highest level of noise or distortion to make the

distortion to make the demodulator demodulator reach anreach an incorrect decision. It is, however, only able incorrect decision. It is, however, only able toto modulate at 1 bit/symbol (as seen in the figure) and modulate at 1 bit/symbol (as seen in the figure) and so is unsuitable for high data-rate applications when so is unsuitable for high data-rate applications when bandwidth is limited.

bandwidth is limited.

Quadrature phase-shift keying Quadrature phase-shift keying

(QPSK):-Sometimes known as quaternary or quadriphase Sometimes known as quaternary or quadriphase PSK, PSK, or

4-PSK, 4-4-PSK, or 4-QAM[QAM[6],6], QPSK uses four pointsQPSK uses four points on the constellation diagram, equispaced around a on the constellation diagram, equispaced around a circle. With four phases, QPSK can encode two circle. With four phases, QPSK can encode two bitsbits per symbol, shown in the diagram

per symbol, shown in the diagram withwith Gray codingGray coding to minimize the BER — twice the

to minimize the BER — twice the rate of BPSK.rate of BPSK. Analysis shows that this may be used either Analysis shows that this may be used either toto double the data rate compared to a BPSK system double the data rate compared to a BPSK system while maintaining the

while maintaining the bandwidthbandwidth of the signal or toof the signal or to maintain the data-rate of BPSK but halve the maintain the data-rate of BPSK but halve the bandwidth needed.

bandwidth needed.

Applications of phase modulation: Applications of phase modulation:

1

1)) PPhhaasse e mmoodduullaattiioon n iis s uusseed d iin n WWiirreelleessss

technology:-The

The wireless LANwireless LAN standard,standard, IEEE 802.11bIEEE 802.11b, uses a, uses a variety of different PSKs depending on the data-rate variety of different PSKs depending on the data-rate

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required. At the basic-rate of 1

required. At the basic-rate of 1 Mbit/Mbit/s, it usess, it uses DBPSK (differential BPSK). To provide the DBPSK (differential BPSK). To provide the extended-rate of 2 Mbit/s, DQPSK is used. In extended-rate of 2 Mbit/s, DQPSK is used. In reaching 5.5 Mbit/s and the full-rate of 11 Mbit/s, reaching 5.5 Mbit/s and the full-rate of 11 Mbit/s, QPSK is employed, but has to be coupled with QPSK is employed, but has to be coupled with complementary code keying

complementary code keying..

The higher-speed wireless LAN standard, IEEE 802.11g The higher-speed wireless LAN standard, IEEE 802.11g hashas

eight data rates: 6, 9, 12, 18, 24, 36, 48 and 54 eight data rates: 6, 9, 12, 18, 24, 36, 48 and 54 Mbit/s. The 6 and

Mbit/s. The 6 and 9 Mbit/s modes use OFDM9 Mbit/s modes use OFDM modulation where each sub-carrier is BPSK modulation where each sub-carrier is BPSK modulated. The 12 and 18 Mbit/s modes use modulated. The 12 and 18 Mbit/s modes use OFDM with QPSK. The fastest four modes use OFDM with QPSK. The fastest four modes use OFDM with forms of

OFDM with forms of quadrature amplitudequadrature amplitude modulation

modulation..

Because of its simplicity BPSK is Because of its simplicity BPSK is appropriate for low-cost passive transmitters, and appropriate for low-cost passive transmitters, and is used in

is used in RFIDRFID standards such asstandards such as ISO/IEC 14443ISO/IEC 14443 which has been adopted for

which has been adopted for biometric passports,biometric passports, credit cards

credit cards and many and many other applications.other applications.

Bluetooth

Bluetooth 2 will use π / 4-DQPSK at its lower rate (22 will use π / 4-DQPSK at its lower rate (2 Mbit /s) and 8-DPSK at its higher rate (3 Mbit /s) Mbit /s) and 8-DPSK at its higher rate (3 Mbit /s) when the link between

when the link between the two devices is sufficientlythe two devices is sufficiently robust. Bluetooth 1 modulates with

robust. Bluetooth 1 modulates with GaussianGaussian minimum-shift keying

minimum-shift keying, a binary scheme, so either , a binary scheme, so either modulation choice in version 2 will yield a higher modulation choice in version 2 will yield a higher data-rate. A similar technology,

data-rate. A similar technology, IEEE 802.15.4IEEE 802.15.4 (the(the wireless standard used by

wireless standard used by Zig BeeZig Bee) also relies on) also relies on PSK. IEEE 802.15.4 allows the use of two

PSK. IEEE 802.15.4 allows the use of two frequency bands: 868–915

frequency bands: 868–915 MHzMHz using BPSK and atusing BPSK and at 2.4

2.4 GHzGHz using OQPSK.using OQPSK.

2) Phase modulation is also used in signal 2) Phase modulation is also used in signal transmission sy

transmission system in army stem in army . It helps to transmit. It helps to transmit video signal along with the audio signal. Thus video signal along with the audio signal. Thus phase modulation is used in

phase modulation is used in communication systemcommunication system by army by making the use of

by army by making the use of special receiver special receiver devices which can receive and demodulate both devices which can receive and demodulate both audio and video signal