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TECHNIA International Journal of Computing Science and Communication Technologies, VOL. 3, NO. 1, July 2010. (ISSN 0974-3375)
551
ANALOG & DIGITAL MODULATIONTECHNIQUES: AN OVERVIEW
D.K.Sharma1, A. Mishra2 & Rajiv Saxena3
1Ujjain Engineering College, Ujjain, MP2Madhav Institute of Technology & Science, Gwalior, MP3Jaypee Institute of Engineering & Technology, Guna, MP
1dilip_sharma1172@yahoo.com; 2drabhaymishra@yahoo.com; 3rajiv.saxena@jiet.ac.in,
Abstract:A tremendous technological transformation during the last twodecades has provided a potential growth in the area of digitalcommunication and lot of newer applications and technologiesare coming up everyday due to these reasons. Restrictingoverself to the domain of modulation techniques a briefoverview over different analog and digital modulationtechniques has been provided in this article through extensiveliterature survey in a tabular manner enabling to analyze andestablish the superiority at a glance of a specific modulationtechnique for a particular application.
1.0 INTRODUCTION:Living in the era of communication every thing
may be video, audio or any information in the form ofelectrical signal is termed as data and there is an enormousrequirement of data transfer between two or more pointthrough the world wide web, every moment of the clock,which is a big threaten to the existing communicationsystems because of the problems like spectral congestion,severe adjacent & co-channel interference problems andnoise corrupted data reception etc. This has resulted inserious need for the research work all around the world forthe development of the communication systems which canhandle the above said problems, where each aspect of thecommunication systems is dealt with the development ofnew encoding techniques, modulation techniques,possibilities for newer transmission channels and off coursethe demodulation and decoding techniques [1, 2].
The design of a communication system is applicationoriented and is dependent on the type of the signal. Thechoice of digital communication technique over its analogcounter part becomes more evident of the fact that it providelarger immunity to noise for even at the price of largebandwidth requirements, where as the requirement of video,Audio and data over the computer network or the mobiletelephony network termed as the third generation (3G)mobile communication poses a serious problem for thebandwidth so The existing modulation techniques need to bemodified for the purpose where it can handle both thesituations of noise and bandwidth efficiency [3, 4].
The major advantage of using digital modulationtechnique is that the use of digital signals reduces hardware,noise and interference problems as compared to theanalogue signal where large number of waveforms will berequired resulting in a larger bandwidth for the symbol to betransmitted [5].
Over the past years various modulation techniqueshave been designed and extensively used for variousapplications but the modern communication system requiresdata transmission at a higher rate, larger bandwidth in order
to have multimedia transmission, hence the existing modulationtechniques are not able to provide a complete solution keepingthis in the view the authors of this article have tried to draw asketch within the existing modulation techniques to derive outexactly what modifications or the alterations in the presenttechniques may sort out the problem or there is still a need fordesigning a new modulation technique for the purpose of thepresent communication system requirements [6, 7].
2.0 Classification of Modulation Techniques.Modulation is the process of varying some parameter of
a periodic waveform in order to use that signal to convey amessage. Normally a high-frequency sinusoidal waveform isused as carrier signal. For this purpose ,if the variation in theparameter of the carrier is continuous in accordance to the inputanalog signal the modulation technique is termed as analogmodulation scheme if the variation is discrete then it is termed asDigital Modulation Technique [8].
Table-1: Type of Modulation TechniquesSr.No
.ModulationTechniques
Type Notation
01 AnalogModulationTechniques
(i) AmplitudeModulation
(ii) FrequencyModulation(iii) Phase
Modulation
A.M.
F.M.
P.M.
02 DigitalModulationTechniques
(i) AmplitudeShift Keying
(ii) FrequencyShift Keying
(iii)Phase ShiftKeying
A.S.K.
F.S.K.
P.S.K.
2.1 Analog Modulation Techniques:-There are basically three type of analog modulation
schemes the amplitude modulation , the Frequency modulationand the phase modulation schemes which have in turn lot ofclass, subclass or derivatives as listed in Table-2 [9, 10]. In caseof the Amplitude Modulation there are several derivatives and itis evident from the comparative table -3 that the Single SideBand Suppressed Carrier (SSS-SC) has smaller bandwidth andpower requirements in contrast with Double Side BandSuppressed Carrier (DSB SC) and Double Side Band FullCarrier (DSB FC) and Single Side Band Full Carrier (SSB FC)but for detection of this signal, we require sharp cutoff Low PassFilter (LPF) which is not practically viable. Using the VestigialSide Band (VSB) technique in place of (SSB SC), we can
TECHNIA International Journal of Computing Science and Communication Technologies, VOL. 3, NO. 1, July 2010. (ISSN 0974-3375)
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achieve a low pass filter with a gradual cut off but it requiresmore BW and power than SSB-SC and less then the DSB-SC and DSB-FC and hence ideally SSB-SC is proves to bebetter than other AM schemes but practically, VSB provesto be a much better candidate then the other amplitudemodulation techniques [11, 12].
The Amplitude modulated signals require nonlinearamplifiers which generate spurious out-of-band spectralcomponents which are filtered out with a great difficulty.Frequency Modulation proves to be better in comparison toamplitude modulation and phase modulation, and thederivative of frequency modulation, narrow band FM(NBFM) is usually employed to overcome above mentionedproblems in the communication system [13, 14].Table-3 provides representation, bandwidth requirement andpower requirement properties of various analog modulationtechniques. The great merit of FM over AM is that FMallows us to suppress the effects of noise at the expense ofbandwidth. The major limitation of the analog modulationsystems for communicating over long channels is that oncenoise has been introduced at any place along the channel,then it is carried out till the end. Because the analogmodulation system ( AM, FM and PM ) are extremelysensitive to the noise present at the receiver end in contrastto this if a digital signal is modulated and transmitted thereceived signal is far less sensitive to receiver .
2.2 Digital Modulation Techniques:-After the conversion of an Analog signal to digital
by sampling different type of digital modulation schemescan be achieved by the variation of different parameter ofthe carrier signal for example the Amplitude variation givesBASK, Frequency variation gives BFSK and the phasevariation gives BPSK. Also sometimes a combinationalvariation of this parameter is done to generate the hybridmodulation technique viz. a combinational variation ofAmplitude and Phase Shift Keying (APSK). Many moredigital modulation techniques are available and can also bedesigned depending upon the type of signal and theapplication [17].
Thus a better digital modulation technique is to bethought over by the designer which has an ability ofexploiting the available transmitted power and thebandwidth to its full extent [18, 19].
In order to achieve a discrete signal it is essential tohave the modulating signal of the form of a NRZ rectangularpulse thus yielding the modulated parameter as a discretesignal switching or keying between two discrete values [20].However, ASK, FSK, and PSK with Nyquiste pulse shapingat the base band form the basic technique of digitalmodulation, but other methods are also possible withhybridization of two or more basic digital modulationschemes with or without pulse shaping [21, 23].
3. Classification of Digital Modulation.These digital modulation techniques can be
classified basically either on the basis of their detectioncharacteristics or in terms of their bandwidth compactioncharacteristics [24]. Various types of digital modulationtechniques are listed in Table-4 and few of them have beencomprehensively emphasized here in details providing acomparative analysis.
3.1 Binary Amplitude Shift Keying [BASK]The BASK is obtained by the alteration of the
amplitude of the carrier wave [1, 11]. It is a coherent modulationtechnique hence the concept of the co-relation between thesignal, number of basis functions, the I and Q components andthe symbol shaping are not applicable here. It has very poorbandwidth efficiency. The basic merit of this technique is itssimple implementations but is highly prone to noise and theperformance is well established only in the linear region whichdoes not make it a viable digital modulation technique forwireless or mobile application in the present scenario. Thecombination with PSK [20] yields derivatives like QAM and M-Ary ASK, which have much important application withimproved parameters.
3.2 Binary Frequency Shift Keying [BFSK]When two different frequencies are used to represent
two different symbols, then the modulation technique is termedas BFSK.BFSK can be a wideband or a narrow band digitalmodulation technique depending upon the separation betweenthe two carrier frequencies, though cost effective and providessimple implementations but is not a bandwidth efficienttechnique and is normally ruled out because of the receiverdesign complexities [1-3, 12].
3.3 Binary Phase Shift Keying [BPSK]When the phase of the carrier wave is altered with
reference of the modulating signal then the resultant modulationscheme is termed as Phase Shift Keying. The digital modulationtechnique can be said to be the simplest form of phasemodulation and is known as binary because the carrier phaserepresents only two phase states [13]. It is normally used for highspeed data transfer application, provides a 3dB power advantageover the BASK modulation technique and is robust and simple inimplementation but proves to be an inefficient user of theprovided bandwidth and is normally termed as a non-linearmodulation scheme. It provides small error rates than any othersystems. The modulation techniques provide a number ofderivatives [20].
3.4 Differential Phase Shift Keying [DPSK]For the perfect detection of a phase modulated signal, it
become evident that the receiver needs a coherent referencesignal but if differential encoding and phase shift keying areincorporated together at the transmitter then the digitalmodulation technique evolved is termed as Differential PhaseShift Keying [1, 14]. For the transmission of a symbol 1, thephase is unchanged whereas for transmission of symbol 0, thephase of the signal is advanced by . The track of the phasechange information which becomes essential in determining therelative phase change between the symbols transmitted. Thewhole process is based on the assumption that the change ofphase is very slow to an extent that it can be considered to bealmost constant over two bit intervals (7).
3.5 Quadrature Phase Shift Keying (QPSK)Another extension of the PSK digital modulation technique
is the division of the phase of the carrier signal designed byallotting four equally spaced values for the phase angle [1-3] as
BPSK by having the information capacity double to it, i.e. the
TECHNIA International Journal of Computing Science and Communication Technologies, VOL. 3, NO. 1, July 2010. (ISSN 0974-3375)
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QPSK has four message points in the constellation diagramand so it becomes a highly bandwidth efficient digitalmodulation technique. But the exact phase retrieval becomesa very important factor for the receiver designconsiderations, failing which can give rise to erroneousdetection of the signal. This factor increases the receiverdesign complexities. To compensate for these problems,normally the idea of pulse shaping the carrier modulatedsignal is employed with the Root Raised Cosine Pulseshaping for achieving better performances which in turnprovides a demerits that the constant envelope property ofthe signal is lost but then there is a lost but there is aremarkable improvement in the ISI performance of thisdigital modulation technique [15-18].
3.6 Minimum Shift Keying [MSK]Minimum Shift Keying (MSK) is a modified form of
continuous phase FSK. Here, in this case, the spacingbetween the two carrier frequencies is equal to half of the bitrate which is the minimum spacing that allows the twofrequencies states to be orthogonal [1-3].
An MSK signal can e said to be derived from either anOffset Quadrature Phase Shift Keying (OQPSK) signal byreplacing a square pulse by ½ cosinusoidal pulse oralternatively from an FSK signal. The information capacityof an MSK signal is equal to that of QPSK signal but due tothe ½ cosine pulse shaping the bandwidth requirement islesser than that required by QPSK. It achieved smoothphase transitions thus providing a constant envelope. It haslower out of band power and can be said to be morespectrally efficient than the QPSK modulation technique[19-25].
The major demerits which this digital modulationscheme suffer s is that it is in the class of linear modulation.The spectrum is not enough compact to realize [27] data rateapproximating RF channel bandwidth. Table-2 [26, 27]summarizes representation and different properties of thistechnique.
3.7 Gaussian Minimum Shift Keying [GMSK]An MSK signal is generated by applying a half
sinusoidal pulse in place of a square pulse. If a Gaussianpulse shape is used instead then the resultant digitalmodulation technique is an improved version of the MSKdigital modulation technique in the sense of bandwidth andspectral efficiency and is termed as GMSK digitalmodulation technique (Gaussian Minimum Shift Keying).Moreover, the major advantage in this technique is thesufficiently lower side lobe levels and the narrower mainlobe as compared to a QPSK and MSK pulse [18].
GMSK can be viewed as either a frequency orphase modulation scheme, although the rate of change ofphase is limited by the Gaussian response but he phasecarrier can still advance or retard up to 90o over the courseof the bit period. The severity in pulse shaping lies on thebandwidth time product (BT) because of the reason that theachieved phase change over a bit period may fall short by
act on bit error rate [28] butit still provides improved bandwidth efficiency over MSK.
The bandwidth of a GMSK system is defined bythe relationship between the premodulation filter bandwidthB and the bit period TB. Thus the decision of value of BT
and data rate is crucial in the sense that there has to be a trade ofbetween the BER and out of band interference [29, 30] as thenarrow filter will result in provocation of Inter SymbolInterference (ISI) which on the other hand will reduce the signalpower enormously [30].
The generation of a GMSK signal can be done by anyone of the two methods as in the case of MSK signals, theFrequency Shift Keying modulation method. Only differencewhich comes in here than the generation of MSK signal is thatthe pulse shaping by half root raised cosine pulse is replaced by aGaussian pulse shape.
3.8 Orthogonal Frequency Division Multiplexing (OFDM):-The OFDM is a modulation scheme having multicarrier
transmission techniques here the available spectrum is dividedinto many carriers each one being modulated at a low rate datastream. The spacing between the carriers is closer and thecarriers are orthogonal to one another preventing interferencesbetween the closely spaced carriers hence OFDM can be thoughtof as a combination of modulation and multiplexing techniques,each carrier in a OFDM signal has very narrow bandwidth so theresulting symbol rate is low which means that the signal has hightolerance to multipath delay spread reducing the possibility ofinter symbol interferences (ISI) which is the requirement for
The higher is the transmission rate, the large will be thebandwidth of the signal as compared with the coherencebandwidth of the propagation channel, at this stage the differentspectral components present in the signal will experiencedifferent fading characteristics, this frequency selective fadinghas to be characterized using appropriate techniques in order toachieve acceptable error rate at the detection or output in order toachieve characterization in frequency selective fading the basicapproach is to partition the signal into frequency bands, each oneof which is narrow as compared to the coherence bandwidth ofthe channel and subsequently each of this signal component isthen modulated onto a different sub carrier and the signalcomponents are sent parallel over the channel. Hence, eachsignal component will now experience non- frequency-selectivefading because now the high rate serial data sequence isconverted into a number of lower rate parallel sequences andthen each of them is modulated onto a sub carrier, the effectivemethod to achieve this is orthogonal frequency divisionmultiplexing (OFDM). The modulation parameters dependent onthe data rate used shall be set according to (Table-12) RateDependant Parameter.
4.0 ComparisonThe BASK technique is simpler and economic in
implementation and is less prone to errors but provides lessbandwidth efficiency and operates efficiency in the linear regiononly, which does not make it an efficient technique for thewireless communication systems. On the other hand, he BFSKtechnique is still less prone to errors and the bandwidthrequirement is the same as that of BASK (Table-4) but is not abandwidth efficient technique. The error performance parameteris better to BASK (Table-9,10). It requires matched filerdetection and because of this, the receiver design complexitiesincrease and so it is seldom used for wireless or mobileapplication.
The BPSK modulation technique is still better than theabove mentioned two modulation techniques. It is a coherent
TECHNIA International Journal of Computing Science and Communication Technologies, VOL. 3, NO. 1, July 2010. (ISSN 0974-3375)
554
modulation technique and can be used for high speed datatransfer application and has a basic advantage of doubleinformation capacity (Table-7) over BASK and BFSK.Simple implementation and robustness makes it a usefultechnique for satellite communication but on the other handit has proved an inefficient use of the bandwidth and iscategorized under a class of non-linear modulationtechniques (Table-5). The error performance is better and isoptimized to achieve minimum possible error rate (Table-6,7). The detection of phase shift (Table-8) makes thereceiver design complex, so the technique is not of interestfor the wireless or mobile communication applications.
The DPSK technique provides information capacitysimilar to BPSK and is considered to be more viabletechnique than BPSK and is a non coherent orthogonalmodulation (Table-4, 5). But the receiver complexities aremore than BPSK because memory is required in the systemto keep the track of relative phase difference.
The most widely used technique is the QPSK modulationtechnique which has an information capacity double toBPSK (Table-4) over the same bandwidth and requirescoherent detection, so it can be considered to be highly BWefficient. Since the modulation envelope is also constanthence it is said to be spectrally efficient modulationtechnique also. Thus it provides major advantages overBPSK and has also overcome the major drawbacks of theBPSK.
In detection of a QPSK signal, the detection of exactphase shit becomes an important criterion which on theother hand increases receiver design complexities as well.The improvement further in this modulation technique canbe achieved by pulse shaping the modulated carrier. Thepulse shaping by ½ co-sinusoidal pulse shaping provides abetter performance modulation technique, the MinimumShift Keying (MSK), which can also be viewed ascomprising of two CPFSK signals. This has a majoradvantage that the out of band power is significantly lowerthan QPSK (Table-7) and the 99% of total power of MSK is1.2 TB thus spectrally efficient and constant envelopes. Ithas proved to be a better modulation technique than QPSKin the sense that the signal coherence and deviation ratio arelargely unaffected by variation in input rates (Table 11).But the basic demerit (Table 7) of MSK modulationtechnique is that the spectrum is not enough compact for therealization of higher data rates. The GMSK modulationtechnique is a variation of MSK where the co-sinusoidalpulse shaping of the modulated carrier is replaced by theGaussian pulse shaping. This improves the envelope andthe spectral efficiency (Table 6, 7). A BT = 0.3 GMSK hasbeen more popular than its other variants as it is optimizedfor the better bandwidth and error performances at thisvalue. The major disadvantage shown by this modulationtechnique is its high susceptibility to ISI at higher data ratesdue to the narrow symbol shape (Table 7). The technique ishighly used in GSM mobile communication.
The average probability of bit error at the output of ademodulator and decoder is the performance measure of thedemodulator decoder combination. To be more precise theprobability of error is a function of code characteristics,waveforms, the transmitted power, characteristics of thetransmission channel and the demodulation and decodercombination. Hence the reconstructed signal at the receiving
end is an close approximation of the transmitted signal and thedifference or some function of the difference in the original andthe reconstructed signal. This marks a measure of performance interms of distortion in a digital communication system. (Table-10) summarizes the BER equations of digital modulationtechniques.
The basic research work carried out in the field ofcommunication lead to the development of new modulationtechniques, coding techniques, error rate performances analysisbut the ever increasing demand of the faster communicationsystem with large bandwidth requirements has again generated anew hunger towards the development of newer techniques, somany modulation techniques like BPSK, DPSK, MSK, GMSK,M-ary QAM have been developed. The major consideration withany modulation technique developed is that its detectionperformance should show a better bit error rate (BER)performance, several methods have been devised for the exact orimproved BER performances of the modulation techniques.
The main objective of a communication systemdesigner is to transmit message as speedily as possible, with leastprobability of error. Fast communication is possible by: (i)reducing the time of each massage; but this, in turn, increase thebandwidth and (ii) simultaneous transmission of severalmessages over a single physical channel. This process is knownas multiplexing. So OFDM can be a good candidate over otherdigital modulation schemes.
5.0 Conclusions:An analysis of the digital modulation technique carried
out in this article reveals that the selection of a digitalmodulation technique is solely dependent on the type ofapplication. This is because of the fact that some of thetechnique provide lesser complexities in the design of themodulation and demodulation system and prove economic likethe BASK, BFSK, BPSK and DPSK techniques and can bevisualized for the systems which really does not require highamount of precisions or when economy is the major aspect andthe BER performances can be tolerated.
On the other hand when the system designer has a soleconsideration for the techniques like BASK, BFSK, BPSK and
designer has to think in terms of better modulation techniqueslike the QPSK, MSK and GMSK, where GMSK has proved itsperformance over the other two in the area of mobilecommunication because of the spectral efficiency. But the
criterion for higher data rate communication is taking the lead inalmost every area of communication and thus the ISI and BERrealization become very important and crucial aspect for anyfuture digital modulation technique.
Taking the above facts into consideration, the design ofa digital communication system is very trivial and is very muchapplications oriented, as one application may require higherprecision in data reception where as the other may compromiseon this aspect but may be rigid on the aspect of the availablebandwidth or power, thus the parameters like the modulationbandwidth, power, channel noise and the bit error rate becomevery important parameters in the designing of digital/wirelesscommunication system.
Reference:
TECHNIA International Journal of Computing Science and Communication Technologies, VOL. 3, NO. 1, July 2010. (ISSN 0974-3375)
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Table-2: Classification of Analog Modulation TechniquesSr.No. MODULATION
TECHNIQUESREPRESENT
ATIONTYPE
1Amplitude Modulation
Double-SidebandSuppressed Carrier
AMDSB-SC Linear
2Amplitude Modulation
Double-Sideband With FullCarrier
AMDSB-FC
Linear
3Amplitude Modulation
Single-Sideband SuppressedCarrier
AMSSB-SC
Linear
4Amplitude Modulation
Single-Sideband With FullCarrier
AMSSB-FC
Linear
5Amplitude Modulation
Vestigial-SidebandAMVSB
Linear
6 Narrow-Band FrequencyModulation
NBFM Non-Linear
7 Wide-Band FrequencyModulation
WBFM Non-Linear
8 Phase Modulation PM Non-Linear
Table-3: Performance Analysis of Analog Modulation Schemes
Sr.No.
TYPE OFANALOG
MODULATION
BANDWIDTH
(B. W.)
%POWERSAVING
POWERREQUIREM
ENT
1 AM-DSB-FCm2 Standard 3/2 Pc
2 AM-DSB-SCm2 66.67% 5/4 Pc
3 AM-SSB-FCm
16.67% 1/2 Pc
4 AM-SSB-SC m 83.33% 1/4 Pc
5 AM-VSB m >SSB-SC Greater thanSSB-SC
6 NBFMm2 Same as
DSB-SCSame asDSB-SC
7 WBFMFm
.
Morethan
NBFM
More thanNBFM
m =
modulatingfrequency
F =modulation index in
FM
P =modulation in PM
Pc = carrierpower
Table 4: Classification & Performance Analysis of Digital ModulationTechniques [1-7]
Sr. Modulation Representation Type BW
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No. Technique requirementBinaryModulationScheme
01BinaryAmplitudeShift Keying
BASK Noncoherent 2RB
02BinaryFrequencyShift Keying
BFSK Noncoherent 2RB
03 Binary PhaseShift Keying BPSK Coherent 2RB
04DifferentialPhase ShiftKeying
DPSK Noncoherent 2RB
QuadratureModulationScheme
01QuadraturePhase ShiftKeying
QPSK Coherent 2RB
02MinimumPhase ShiftKeying
MSK Coherent Less thanQPSK
M-rayModulationScheme
Where
NMN ,2
01 M-ary PhaseShift Keying M-ary PSK Coherent 2 /N
02
M-aryQuadratureAmplitudeShiftModulation
M-ary QAM Coherent2 /N
03M-aryFrequencyShift Keying
M-ary FSK Coherent M 2 /N
OrthogonalFrequencyDivisionMultiplexing
OFDM Coherent
01Binary PhaseShift KeyingOFDM
BPSK-OFDM CoherentLess than
Othertechniques
02
QuadratureAmplitudeModulationOFDM
QAM-OFDM CoherentLess than
Othertechniques
03
16-QuadratureAmplitudeModulationOFDM
16-QAM-OFDM
Coherent
Less thanOther
techniques
04
64-QuadratureAmplitudeModulationOFDM
64-QAM-OFDM Coherent
Less thanOther
techniques
Table-11: Modulation Parameters of Digital Modulation Techniques inmulticarrier Modulation Schemes
Sr. Data Modulati Codin Coded Coded Data
No.
Rate(Mbits/s)
on gRate( R )
bitsPerSub-carrier
BPSC
bitsPerOFDMSymbol
CBPS
bitsPerOFDMSymbol
DBPS
1 6 BPSK ½ 1 48 24
2 9 BPSK ¾ 1 48 36
3 12 QPSK ½ 2 96 48
4 18 QPSK ¾ 2 96 72
5 24 16-QAM ½ 4 192 96
6 36 16-QAM ¾ 4 192 144
7 48 64-QAM 2/3 6 288 192
8 54 64-QAM ¾ 6 288 216
Table-12: Numerical Values for the OFDM [Multicarrier Modulation Schemes]Parameters
Sr.No.
PARAMETERS VALUE
1 Sampling Rate = 1/T 20Mhz
2 Useful Symbol Part Duration 64*T3.2 microsecond
3 Cyclic Prefix Duration 16*T, 0.8 Sec. (mand.)8*T, 0.4 Sec. (Opti.)
4 Symbol Interval 80*T, 4 Sec, +
72*T +
5 Number of Data Sub-carriers
SD
48
6 Number of Pilot Sub-carriers
SP
4
7 Total Number of Sub-
carriers ST
52 ( SD + SP )
8 Sub-carrier Spacing F 0.3125 Mhz ( 1/ )
9 Spacing Between the twooutmost sub-carriers
16.25 Mhz
( ST F )
10 FFT Size, FFT64
11 Used Sub-carrier index { -26 to -1 , +1 to +26 }
Table-6: Parametric Study of Digital Modulation Techniques [1, 8-30]Sr. Digital No. of Type of No. of Message Information BW BW Efficiency Symbol
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557
No. ModulationTechnique
Type
Symbols Envelope points Capacity required Shaping
01 BASK 01 NotConstant 01 Poor 2RB Poor Not required
O2 BFSK 01 Constant 01 Better thanBASK (NC) 2RB Not BW Efficient Not required
03 BPSK 02 Constant 02 Double toBFSK (NC) 2RB
Used for Highspeed datatransfer
Not required
04 DPSK 02 Constant 01 Same asBPSK 2RB
For Mediumspeedcommunication
Not required
05 QPSK 04 Constant04
Expressed interms of SignalEnergy/Symbol
Double ofBPSK 2RB
Highly BWefficient
Required,RectangularPulse
06 MSK 04 Constant04
Expressed interms of Signal
Energy/Bit
Same asQPSK
Less thanQPSK
Out of BandPowerSignificantlylower thanQPSK, 99% oftotal Power ofMSK is 1.2TB
RequiredHalf Co-Sinusoidalpulse
07 GMSK 04 Constant 04 Same asMSK
Narrow BT-0.3 popular Excellent
RequiredGaussianPulse
08
OFDMBPSKOFDMQAM-OFDM
16-QAM64-QAM
02041664
NotConstant
02041664
HighThanabove
Less thanOther
techniques
ExcellentThanabove
Better thanAboveSchemes
Table-7: Merits & Demerits of Digital Modulation Techniques [1, 7-14, 19-30]Sr.No.
Type of DigitalMode Tech Derived From MSLL Merits Demerits
01 BASK ASK - 13 db Simple implementation, low costNot an BW efficient
technique, more noiseprone, operates only in
linear region02 BFSK FSK - 13 db Simple implementation, low cost Received design complex
03 BPSK PSK - 13 dbSimple implementation, robust, used
mostly for satellite communication, 3 dBPower advantage over BASK
Inefficient use of BW, non-linear modulation scheme
04 DPSK PSK - 13 db Reduces complexities of Receiver designfor non coherent case
Efficient less than coherentPSK
05 QPSK PSK - 13 dbTwice the data in same BW, hence BWefficient, more spectrally efficient than
BPSK
Complex receiver design,pulse shaping is required
but then it losses itsconstant envelope property
06 MSKFrom OQPSK byreplacing squarepulse by ½ Co-sinusoidal pulse
- 13 db
Constant envelope, out of band power islower, minimum spacing allows two
frequencies to be orthogonal, spectrallyefficient and easily generated, smoothphase transition as compared to QPSK
Linear modulation, thespectrum is not compact
enough to realize data ratesapproximating rf CHANNEL
bw
07 GMSK
From FSK byreplacing ½ Co-Sinusoidal pulse
by Gaussianpulse
Fast roll of factorwith BT = 0.3,
narrow main lobe,lower side lobe
level
Constant envelope, spectrally efficient,widely used in GSM mobile
communication with BT = 0.3Promotes ISI at higher bit
rate transmission
08
OFDM
BPSK-OFDMQAM-OFDM
16-QAM64-QAM
From multicarriermodulation
scheme__
Robust to ICI & ISI, High SpectralEfficiency, Efficiently implementation by
FFT, Low sensitivity to timesynchronization errors, Tuned sub channelreceiver filter are not required, Facilitates
single frequency network i., Complexequalization.
1. Sensitive to Doppler Shift.2. To frequency
synchronization problem. 3.Inefficient transmitter power
consumption since linearpower amplifier is required.
Table 8: Detection Performance Analysis of Digital Modulation Techniques [1-7, 19-30]
Sr.No.
DigitalModulationTechniques
Demodulation Performance Combination with othertechniques Derivatives
01 BASK Simple demodulation With PSKQAM Quadrature AmplitudeModulation (used extensively indigital microwave links M-ray ASK
02 BFSK Simple demodulation (Matched filter Special case of orthogonal M-ray FSK
TECHNIA International Journal of Computing Science and Communication Technologies, VOL. 3, NO. 1, July 2010. (ISSN 0974-3375)
558
detection) modulation
03 BPSK Phase shift detection makes the Rxcomplex With ASK-QAM
QAM, incoherent detection, QPSK,OQPSK, BPSK, /4PSK, 16 PSK,MPSK
04 DPSKReceiver requires memory to measurerelative phase difference between waveforms received in successive intervals
Non coherent orthogonalmodulation when consideredover two bit interval
/4 DPSK
05 QPSK Phase shift detection is importantDifferent phase variation.Replacement of a square pulseby ½ sinusoidal pulse to giveMSK
OQPSK-Q channel shifted by ½symbol QPSK to OQPSK to
/4 QPSK when differentiallydecoded referred to as /4 DQPSK
06 MSK Direct injection of NRZ data to frequencymodulator with Modulation Index 0.5
Replacement of ½ co-sinusoidalpulse by Gaussian pulse to giveGMSK
GMSK
07 GMSKBandwidth time product BT is an importantfactor performance is measured by SNRversus BER
Nil GMSK BT = 0.3GMSK BT = 0.5
08 OFDMBandwidth time product BT is an importantfactor performance is measured by SNRversus BER
BPSK,QAM,16-QAM,64-QAM
BPSK,QAM,16-QAM,64-QAM
Table-9: Performance Characteristics of Digital Modulation Techniques (1-7, 12-18)
1 DigitalModulationTechnique
ErrorProbability
ErrorPerformance
ISIStatus
Dimensions
No.ofBasisFunctions
01 BASK
BWAmplitudeNoisepower
for
o
o
,,,
,8
exp21 2
2 Efficient only in linearregion
Nil One One
02 BFSK
,&&
,2
exp21
densityBitNoisebo
Performs Well at high
values as PSK &
FSK for same signalenergy and bit rate.
Nil One One
03 BPSKerfc
21
Small error rate thanany other system butrestriction of AWGN on1 bit decoding .It isoptimum as it achievesminimum possible errorrate.
LessProne
Two Two
04 DPSK
2exp
21
Required is 3
dBless than that ofBFSK for same errorrate.
LessProne
Two Two
05 QPSK 2
Performance better overBPSK & BFSK butmajor draw back is usedof square pulse, can beimproved by shapingwith root raised cosineimproving ISI.
ProneToISI
Two Two
06 MSK 2
The signal coherenceand derivation ratio arelargely unaffected byvariations in input datarate.
LessProneThanQPSK
Two Two
07 GMSK
BTBT
Qe
,85.0,25.0
,68.0,2 The carrier is lag of lead
by090 over bit
period, w.r.t. BTresulting in BER.
MoreProneThanMSK
Two Two
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559
08 OFDM
ddd
WWWerfc
S
TP
22
02
2 221
Minimum than otherschemes
Nil 2 inBPSK4 inQPSK16 in16-QAM
2 inBPSK4 inQPSK16 in16-QAM
Table-10: BER Equations of Digital Modulation Techniques
Sr.No.
MOD.
N
M2
B.W.
1 BPSK 2,1
2 QPSK 4,2 /
23 SQPSK 4,2 /
24 MSK 4,2 /
25 M-PSK M,N /
N6 16-
QAM16,4 /
47 M-
QAMM,N /
N8 QPR L
levels
/
49 LQPR L
levels
]/})1{
/6()(log4/[]/11[2
2/12
2/122
ob NELL
erfcL/
L
10
M-FSK M,N M
/
L11
OFDM-BPSK 2
.1cos
cossin
21 1
0
21
022
fmkfmkcwhere
dcEecE
mP
Imk
N
kmk
Imk
o
I
bMinimumB.W.
isrequir
edthanotherschemes
12
OFDM-QPSK
4
Qmk
kmk
mk
Qb
ccewhere
dccm
coscos
.cossin21
1
0
21
000
22
MinimumB.W.
isrequir
edthanotherschemes
13
OFDM-16QA
M
1600
0001QQ
iMinimumB.W.isrequir
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560
1
0
21
000
002
.cos2coscos2cos
.cos2cossin2sin2sin221
22
kmk
Qmk
Qmkmkmk
QQi
dcdcdcdce
ddcdcdcdcdmedthanotherschemes
Table 5: Mathematical Representation of Digital Modulation Techniques [1-8, 17, 18]
Mod. Mathematical Representation Type Correlationbetweensignals
Component Q component
1 BASK X(t) = Am (t) cos2 fct for 0 < 1 < TB, m(t) = 1 for Bit 1 & 0 for Bit 0Signal energy representation
X(t) = tfTE
cB 2cos2
NonCoherent
Noncorrelation
Nil Nil
2 BFSK
Xi(t) =B cos(2 fct) for 0 < t t < TB, i = 1,2 fc =
B
c
X1 (t) = 1, (f1) & X2 (t) = 0, (f2) and
NonCoherent
Noncorrelation
Nil Nil
3 BPSK
X1(t) =B
B
TE2
cos(2 fct) & X2(t) =B
B
TE2
cos(2 fct+ )
X1(t) for Bit 1 & X2(t) for Bit 0
Coherent Noncorrelation
Nil Nil
4 DPSK Over dual bit interval
X1(t) =
BBcB
B
BcB
B
X2(t) =
BBcB
B
BcB
B
TtTfortfTE
TtfortfTE
2)2cos(2
0)2cos(2
It is a special case of Non coherent Orthogonal Modulation for TB = 2TB & EB= 2EB X1(t) for Bit 1 and X2(t) for Bit 0
Noncoherent
Correlationexists
Nil Nil
5 QPSK(Phasedivision)Phaseangles45,135,225 and315degree
Xo(t) =
)2sin(4
)12sin(2
)2cos(4
)12cos(2
tfnTE
tfnTE
cB
B
cB
B
for 0 < t < TB, Where n = 1`,2,3,4 and forBit 10 00 01 11Phase /4 3 /4 5 /4 7 /4
Coherent Correlationexist
Xt(t) =
B
n = 1, 2, 3, 4
XQ(t) = -
4
)12(sinn
EB
n = 1, 2, 3, 46 MSK
X1(t) = cos 02B
c TtABtf
Where the value of = 0 for A = 1 and the value of = for A = -1. Thusthe above expression can be of the form
(1) X1(t) = cosB
c for A = 1 & B = + 1
Coherent Correlationexist
Xt(t) = +
tT
TE
B
B
B
2cos
2
Tb < 1 < Tb
XQ(t) = +
tT
TE
B
B
B
2
sin
2
Q < 1 < Tb
TECHNIA International Journal of Computing Science and Communication Technologies, VOL. 3, NO. 1, July 2010. (ISSN 0974-3375)
561
(2) X1(t) = cosB
c Tttf2 for A = -1 & B = + 1
7 GPSK
G(t) =
2log5.0
2
2log5.0
2
21
e
Bban
e
Bban
TtBQ
TtBQ
T
Q(t) =t
2
, Bban is the bandwidth of the filter
Coherent Correlationexists
I(t) = cos[C(t)] For C to be aconstant such thatT
T
dttCG2
)(
Q(t) = sin[C(t)]
8 OFDM.0;/2exp1 1
0
ttjt
T = Signal Duration, N = N-Point IDFT,1
=Scale factor,
Signal
samples .1,,.........2,1,0;nn
Sub carrier frequency = =
Sub-carriers. EB = Energy of the Bit, TB = Time duration of the Bit, fc =Carrier Frequency, m(t) = Modulation Index, A = Amplitude, nc = Noise
NonCoherent
Noncorrelation
Nil Nil
9 OFDMWith(BPSK,QAM,16-QAM,64-QAM)
1
0
2k
kk
tfj c
is complex data symbol, T = OFDM block duration, tg = pulse
shape , = carrier frequency.
NonCoherent
Noncorrelation
Nil Nil