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converter, thereby improving DPWM resolution and the efficiency. R.Gandhiraj, Ranjini Ram, K.P.Soman [5] presented a small tutorial for the new users in the.
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Vol.04 Issue-03, (March, 2016) ISSN: 2321-1776 International Journal in IT and Engineering, Impact Factor- 5.343

A Comparative Study of Various Digital Modulation Techniques Harpreet Kaur Channi Department of Electrical and Electronics Engineering Chandigarh University, Gharuan, Mohali, Punjab, India. Abstract— Digital communication is a transfer of information from source to destination in the form of discrete signals. These signals are manipulated by electronic circuits (analog or digital) for making it possible to transmit and receive the data or information. Digital transmission is the physical transfer of data over a point-to-point or point-to-multipoint communication channel such as copper wires (guided and unguided channels), optical fibres, wireless communication channels, and storage media. The data is represented as an electromagnetic signal, such as an electrical voltage, radio wave, microwave, or infrared signal. In communication systems, the noise is an error or undesired random disturbance of a useful information signal, introduced before or after the detector and decoder. The noise is a summation of unwanted or disturbing energy from natural and sometimes man-made sources. If we transmit the baseband signals directly, the signals from different transmitters will get mixed up and the information will be lost. Because of these reasons, we use the technology of modulation, for transmitting message signals effectively for long distances Modulation is the process of varying one or more properties of a high frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted. The main goal of modulation today is to squeeze as much data into the least amount of spectrum possible. That objective, known as spectral efficiency, measures how quickly data can be transmitted in an assigned bandwidth expressed in terms of bits per second per Hz (b/s/Hz). Multiple techniques have emerged to achieve and improve spectral efficiency. There are various analog and digital modulation techniques used to transmit the signals. Due to various advantages of digital signals over analog signals, digital modulation techniques are preferred widely. This paper presents a brief study of different digital modulation methods and their uses for a particular application. Keyword: baseband, bandwidth, Discrete, guided, manipulated, noise.

I.

Introduction

Digital Communication System is a system in which digital signals are transmitted via digital modulation and demodulated as a digital signal at the receiver. Figure 1 illustrates the basic elements of a digital communication system [1].

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Fig 1 Block Diagram of DCS

Source: [4] The source output may be either an analog signal, such as an audio or video signal, or a digital signal, such as the output of a teletype machine, that is discrete in time and has a finite number of output characters. In a digital communication system, the messages produced by the source are converted into a sequence of binary digits. The process of efficiently converting the output of either an analog or digital source into a sequence of binary digits is called source encoding or data compression. The sequence of binary digits called information from the source encoder is passed to the channel encoder. The purpose of the channel encoder is to introduce, in a controlled manner, some redundancy in the binary information sequence that can be used at the receiver to overcome the effects of noise and interference encountered in the transmission of the signal through the channel. This increases the reliability of the received data and improves the fidelity of the received signal [2]. The binary sequence at the output of the channel encoder is passed to the digital modulator, which serves as the interface to the communication channel. The modulation process begins with the data to be transmitted being fed to a DSP device that generates two digital outputs, which are needed to define the amplitude and phase information required at the receiver to recover the data. The DSP produces two baseband streams that are sent to digital-to-analog converters (DACs) that produce the analog equivalents. At the receiving end of a digital communication system, the digital demodulator processes the channel corrupted transmitted waveform and reduces the waveforms to a sequence of numbers that represent estimates of the transmitted data symbols. This sequence of numbers is passed to the channel decoder, which attempts to reconstruct the original information sequence from knowledge of the code used by the channel encoder and the redundancy contained in the received data.

II.

Literature Review

Quadri, F., Tete, A.D. [3] presented the review of the different digital modulation techniques and the various methods and tools that are used to implement it on FPGA along with the design summary and logic utilization of the resources. It includes an approach for the implementation of three modulators mainly Amplitude Shift Keying modulator, Phase Shift Keying modulators and Frequency Shift Keying modulator in VHDL by means of Xilinx 13.1 and simulation in A Monthly Double-Blind Peer Reviewed Refereed Open Access International e-Journal - Included in the International Serial Directories

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Modelsim. The same modulators have also been developed in MATLAB/SIMULINK environment. The various factors that affect the choice of a particular modulation technique have also been discussed and accordingly anyone of the techniques can be adopted taking into consideration the application. Chia-An Yeh, Yen-Shin Lai[4] explained that the resolution of a digital pulse width modulator (DPWM) can be dramatically increased by either constant on-time modulation control or constant off-time modulation control as compared to that for constant frequency modulation. However, the switching frequency increases dramatically for the constant on/off-time modulation method under heavy/light load conditions, respectively. The increase of switching frequency results in more switching losses and requires a higher performance controller. They proposed a new digital pulse width modulation (PWM) technique with constant on/off-time control for a synchronous buck dc/dc converter in order to reduce the switching frequency and switching losses. Moreover, the switching frequency can be limited to a certain range. Experimental results of the proposed new digital PWM technique are presented for confirmation. It was shown that the proposed technique can significantly reduce the switching frequency of the converter, thereby improving DPWM resolution and the efficiency. R.Gandhiraj, Ranjini Ram, K.P.Soman [5] presented a small tutorial for the new users in the field of software defined radio. Applications are build up using graphical user interface called the GNU radio companion (GRC). The idea behind developing such a tool kit is to give practical exposure in the communication concepts like basic signal generations, signal operations, multirate concepts, analog and digital modulation schemes and finally multiplexing schemes with the help of GNU radio. Unlike MATLAB Simulink or Labview GNU radio is open source i.e. free of cost and the concepts can be easily reached to the normal people without much of programming concepts using the pre written blocks. And programmers also have the chance to write their own applications. Dung Nguyen, Hobraiche, J.,Patin, N. , Friedrich, G., Vilain, J.[6] presented direct digital technique-generalized discontinuous pulse width modulation (PWM) - a new implementation method for an optimal discontinuous PWM (DPWM) in terms of switching losses of the inverter on an embedded system. At each sampling period, an optimal choice is done in order to clamp one of the three half-bridges. Its advantages compared to classic ones (DPWM) are as follows: needless to know the load power factor, operational under steady-state and dynamic operating conditions, and low computation time. The proposed algorithm is then verified by simulation. Experimental results, based on a resistance-inductance load and a starter-generator application, are provided to show its effectiveness. K.S. Chong, E. Zahedia,, K.B. Gan, M.A. Mohd. Ali,[7] employed delta modulation (DM) as a compression technique for a high-resolution photoplethysmogram (PPG) signal. To accommodate both clean PPG and signals affected by motion artifacts, the effect of step size is evaluated on the performance of DM in order to optimize this technique before it can be deployed in a wireless data acquisition system. To this end, the PPG was recorded using 16-bit analog-to-digital converter (ADC) at a 1000 Hz sampling rate. In order to take into consideration the effect of the DC and AC of the PPG during the performance evaluation, both the PRMS AC+DC (with DC component) and PRMS AC (without DC component) were estimated. As expected, A Monthly Double-Blind Peer Reviewed Refereed Open Access International e-Journal - Included in the International Serial Directories

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results show that the PRMS AC+DC was lower than PRMSAC at all step sizes. Simulation results show that for clean PPG free of motion artifact the optimum step size required to decompress the PPG is V/(2-15-1) with a PRMSAC = 4.7%; PRMS AC+DC = 0.1%, where V is the dynamic range of the ADC. For PPG affected by motion artifact, the optimum step size required to decompress the PPG is V/(2-14-1) with a PRMS AC = 4.9% and PRMSAC+DC = 0.12%. The closeness of these values to the finest possible step size V/(2-16-1) can be explained by the relatively high sampling rate compared to the Nyquist frequency of the PPG.

III.

Problem formulation

The transmission of digital signals is increasing at a rapid rate. Low-frequency analogue signals are often converted to digital format before transmission. The source signals are generally referred to as baseband signals. The low-frequency signal is often translated to a higher frequency range for efficient transmission. The process is called modulation. The move to digital modulation provides more information capacity, compatibility with digital data services, higher data security, better quality communications, and quicker system availability [8]. The spectral efficiency is a measure of how quickly data can be transmitted in an assigned bandwidth. The units of spectral efficiency are bits/s/Hz (b/s/Hz).The Fundamental limitations of Communication System are noise level and available bandwidth which affects its spectral efficiency [9]-[10]. In communication systems, the noise is an error or undesired random disturbance of a useful information signal, introduced before or after the detector and decoder. The noise is a summation of unwanted or disturbing energy from natural and sometimes man-made sources. Signal to Noise ratio (SNR) is another important factor that influences spectral efficiency. It can also be expressed as the carrier to noise power ratio (CNR). The measure is the bit error rate (BER) for a given CNR value. BER is the percentage of errors that occur in a given number of bits transmitted. As the noise becomes larger compared to the signal level, more errors occur. The signal to noise ratio can be calculated as given by Eq. 1. SNR (dB) = 10*log (Psignal/Pnoise)

(1)

Second factor affecting spectral efficiency is bandwidth. Bandwidth is the information-carrying capacity of a communication channel. The channel may be analog or digital. Analog transmissions such as telephone calls, AM and FM radio, and television are measured in cycles per second (hertz or Hz). Digital transmissions are measured in bits per second. For digital systems, the terms "bandwidth" and "capacity" are often used interchangeably, and the actual transmission capabilities are referred to as the data transfer rate (or just data rate).Shannon developed the channel capacity bound given by Eq.2. C=W log 2 (1+ SNR)

(2)

Where C is the channel capacity in bits per second, W is the channel bandwidth in Hertz, and SNR is the channel signal to noise ratio. The need for modulation can be summarized as follows: A Monthly Double-Blind Peer Reviewed Refereed Open Access International e-Journal - Included in the International Serial Directories

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1. The antenna needed for transmitting signals should have size at least λ/4, where, λ is the wavelength. The information signal, also known as baseband signal is of low frequency (and therefore the wavelength is high). If we need to transmit such a signal directly, the size of the antenna will be very large and impossible to build. Hence direct transmission is not practical. 2. The radiated power by an antenna is inversely proportional to the square of the wavelength. So, if we use high frequency signals, the power radiated will be increased. 3. If we transmit the baseband signals directly, the signals from different transmitters will get mixed up and the information will be lost. Because of these reasons, we use the technology of modulation, for transmitting message signals effectively for long distances. A. Objectives of this Study:  To give a brief introduction and classification of various digital modulation techniques.  To give a comparison of different techniques on the basis of spectral efficiency, bit rate etc.

IV.

Classification of digital modulation

Modulation is the process of varying some parameter of a periodic waveform in order to use that signal to convey a message. Normally a high-frequency sinusoidal waveform is used as carrier signal. For this purpose, if the variation in the parameter of the carrier is continuous in accordance to the input analog signal the modulation technique is termed as analog modulation scheme and if the variation is discrete then it is termed as Digital Modulation Technique [11]. Figure 2 shows the modulation of data using basic modulation techniques. Fig 2: ASK, FSK, PSK

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Digital modulation techniques may be classified into coherent and non-coherent techniques, depending upon whether the receiver is equipped with a phase recovery circuit or not. These digital modulation techniques can also be classified basically either on the basis of their detection characteristics or in terms of their bandwidth compaction characteristics [12]. After the conversion of an Analog signal to digital by sampling different type of digital modulation schemes can be achieved by the variation of different parameter of the carrier signal for example the Amplitude variation gives BASK, Frequency variation gives BFSK and the phase variation gives BPSK. Also sometimes a combinational variation of this parameter is done to generate the hybrid modulation technique viz. a combinational variation of Amplitude and Phase Shift Keying (APSK). Many more digital modulation techniques are available and can also be designed depending upon the type of signal and the application [13].The various digital modulation techniques are: 1. Phase-shift keying (PSK): a. b. c. d. e. f. g. h. 2.

Binary PSK (BPSK), using M=2 symbols Quadrature PSK (QPSK), using M=4 symbols 8PSK, using M=8 symbols 16PSK, using M=16 symbols Differential PSK (DPSK) Differential QPSK (DQPSK) Offset QPSK (OQPSK) π/4–QPSK Frequency-shift keying (FSK) a. Binary Frequency-shift keying (BFSK) b. Audio frequency-shift keying (AFSK) c. Multi-frequency shift keying (M-ary FSK or MFSK) d. Dual-tone multi-frequency (DTMF) 3. Amplitude-shift keying (ASK). a. Binary Amplitude Shift Keying [BASK] 4. On-off keying (OOK) (the most common ASK form) a. M-ary vestigial sideband modulation 5. Quadrature amplitude modulation (QAM) - a combination of PSK and ASK: 6. Continuous phase modulation (CPM) methods: a. Minimum-shift keying (MSK) b. Gaussian minimum-shift keying (GMSK) c. Continuous-phase frequency-shift keying (CPFSK) 7. Orthogonal frequency-division multiplexing (OFDM) modulation: a. discrete multitone (DMT) - including adaptive modulation and bit-loading. 8. Wavelet modulation 9. Trellis coded modulation (TCM), also known as trellis modulation 10. Spread-spectrum techniques: a. Direct-sequence spread spectrum (DSSS) b. Chirp spread spectrum (CSS) A Monthly Double-Blind Peer Reviewed Refereed Open Access International e-Journal - Included in the International Serial Directories

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c. Frequency-hopping spread spectrum The description of the modulation techniques is given below: A. Phase-shift keying (PSK): It is a digital modulation scheme that conveys data by changing, or modulating, the phase of a reference signal (the carrier wave). PSK uses a finite number of phases, each assigned a unique pattern of binary bits. Usually, each phase encodes an equal number of bits. The simplest form of phase shift keying (PSK) is binary phase shift keying (BPSK). It uses two phases which are separated by 180° and so can also be termed 2-PSK. This modulation is the most robust of all the PSKs since it takes the highest level of noise or distortion to make the demodulator to reach an incorrect decision. It is, however, only able to modulate at 1 bit/symbol and so is unsuitable for high data-rate applications when bandwidth is limited. Quadrature PSK is also known as quadriphase PSK, 4-PSK, or 4-QAM. QPSK uses four points on the constellation diagram, equispaced around a circle. With four phases, QPSK can encode two bits per symbol. QPSK transmits twice the data rate in a given bandwidth compared to BPSK - at the same BER. Offset quadrature phase-shift keying (OQPSK) is a variant of phase-shift keying modulation using 4 different values of the phase to transmit. It is sometimes called Staggered quadrature phase-shift keying (SQPSK). π /4–QPSK. Other PSK schemes are shaped-offset QPSK (SOQPSK), Dualpolarization quadrature phase shift keying (DPQPSK) or dual-polarization QPSK., Higher-order PSK. B. Frequency-shift keying (FSK): It is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier wave. The simplest FSK is binary FSK (BFSK). BFSK literally implies using a couple of discrete frequencies to transmit binary (0s and 1s) information. With this scheme, the "1" is called the mark frequency and the "0" is called the space frequency. Minimum frequency-shift keying or minimum-shift keying (MSK) is a particular spectrally efficient form of coherent FSK. In MSK, the difference between the higher and lower frequency is identical to half the bit rate. Audio frequency-shift keying (AFSK) is a modulation technique by which digital data is represented by changes in the frequency (pitch) of an audio tone, yielding an encoded signal suitable for transmission via radio or telephone. Normally, the transmitted audio alternates between two tones: one, the "mark", represents a binary one; the other, the "space", represents a binary zero. AFSK differs from regular frequency-shift keying in performing the modulation at baseband frequencies AFSK is not always used for high-speed data communications, since it is far less efficient in both power and bandwidth than most other modulation modes. C. Amplitude-shift keying (ASK) or ON/OFF Keying (OOK) It is a form of modulation that represents digital data as variations in the amplitude of a carrier wave. The amplitude of an analog carrier signal varies in accordance with the bit stream (modulating signal), keeping frequency and phase constant. This digital modulation scheme is used to transmit digital data over optical fiber, point to point military communication A Monthly Double-Blind Peer Reviewed Refereed Open Access International e-Journal - Included in the International Serial Directories

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applications, etc. Binary 1 is represented by a short pulse of light and binary 0 by the absence of light. The BASK is obtained by the alteration of the amplitude of the carrier wave. It is a coherent modulation technique hence the concept of the co-relation between the signals, number of basic functions. It has very poor bandwidth efficiency. The basic merit of this technique is its simple implementations but is highly prone to noise. The combination with PSK [20] yields derivatives like QAM and Mary ASK, which have much important application with improved parameters. D. Continuous phase modulation (CPM) It is a method for modulation of data commonly used in wireless modems. In contrast to other coherent digital phase modulation techniques, where the carrier phase abruptly resets to zero at the start of every symbol, with CPM the carrier phase is modulated in a continuous manner. Minimum-shift keying (MSK) is a type of continuous-phase frequency-shift keying. MSK is encoded with bits alternating between quadrature components MSK encodes each bit as a half sinusoid. This results in a constantmodulus signal, which reduces problems caused by non-linear distortion. Gaussian minimum shift keying or GMSK is a continuous-phase frequency-shift keying modulation scheme. This has the advantage of reducing sideband power, which in turn reduces out-of-band interference between signal carriers in adjacent frequency channels. Continuous-phase frequency-shift keying (CPFSK) is a commonly used variation of frequency-shift keying (FSK), which is itself a special case of frequency modulation. FSK is a method of modulating digital data onto a sinusoidal carrier wave, encoding the information present in the data to variations in the carrier's instantaneous frequency between one of two frequencies referred to as the space frequency and mark frequency. E. Orthogonal frequency-division multiplexing (OFDM) It is a method of encoding digital data on multiple carrier frequencies. OFDM has developed into a popular scheme for wideband digital communication, whether wireless or over copper wires, used in applications such as digital television and audio broadcasting, DSL Internet access, wireless networks, powerline networks, and 4G mobile communications. A large number of closely spaced orthogonal sub-carrier signals are used to carry data on several parallel data streams or channels. Each sub-carrier is modulated with a conventional modulation scheme such as quadrature amplitude modulation or phase-shift keying at a low symbol rate, maintaining total data rates similar to conventional single-carrier modulation schemes in the same bandwidth. The primary advantage of OFDM over single-carrier schemes is its ability to cope with severe channel conditions without complex equalization filters. Channel equalization is simplified because OFDM may be viewed as using many slowly modulated narrowband signals rather than one rapidly modulated wideband signal F. Wavelet modulation It is also known as fractal modulation, is a modulation technique that makes use of wavelet transformations to represent the data being transmitted. One of the objectives of this type of A Monthly Double-Blind Peer Reviewed Refereed Open Access International e-Journal - Included in the International Serial Directories

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modulation is to send data at multiple rates over a channel that is unknown. If the channel is not clear for one specific bit rate, meaning that the signal will not be received, the signal can be sent at a different bit rate where the signal to noise ratio is higher. Spread-spectrum techniques such as direct-sequence spread spectrum (DSSS), chirp spread spectrum (CSS), Frequency-hopping spread spectrum (FHSS) are methods by which a signal (e.g. an electrical, electromagnetic, or acoustic signal) generated with a particular bandwidth is deliberately spread in the frequency domain, resulting in a signal with a wider bandwidth. These techniques are used for a variety of reasons, including the establishment of secure communications, increasing resistance to natural interference, noise and jamming, to prevent detection, and to limit power flux density (e.g. in satellite downlinks).

V.

Results and discussions

The basic research work carried out in the field of communication lead to the development of new modulation techniques, coding techniques, error rate performances analysis but the ever increasing demand of the faster communication system with large bandwidth requirements has again generated a new hunger towards the development of newer techniques, so many modulation techniques like BPSK, DPSK, MSK, GMSK, M-ary QAM have been developed. Table 1gives the spectral efficiency of various digital modulation schemes. Table 2 shows the comparison of modulation schemes on the basis of their merits and demerits. Table 1. Spectral Efficiency for Popular Digital Modulation Methods Type of Spectral efficiency(bits/s/Hz) modulation FSK, 10 (depends upon modulation index and number of subcarriers)

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Table 2. Merits and Demerits of Digital Modulation Techniques Type of Digital Merits Demerits Modulation Low cost, simple More prone to noise, BW inefficient scheme, ASK BASK implementation Operate in linear region. Low cost, simple BFSK implementation Design complexity FSK Constant envelope, spectrally efficient, widely Promotes ISI at higher bit rate transmission GMS used in GSM mobile K Robust, simple implementation, BW inefficient scheme, non-linear BPSK used for satellite modulation scheme communication, power advantage over BASK PSK Reduces complexities of DPSK receiver design for non- Less efficient coherent cases. BW efficient and spectrally QPSK efficient scheme Complex receiver design Constant envelope, spectrally efficient and Linear modulation, the spectrum is not OQPSK MSK easily generated, smooth constant phase transition as compared to QPSK Multi- carrier Robust, high spectral Sensitive to Doppler shift, frequency Modulation OFD efficiency, synchronization synchronization problem. linear power scheme M error amplifier is required

VI.

Conclusions

An analysis of the digital modulation technique carried out in this article reveals that the selection of a digital modulation technique is solely dependent on the type of application. This is because of the fact that some of the technique provide lesser complexities in the design of the modulation and demodulation system and prove economic like the BASK, BFSK, BPSK and DPSK techniques and can be visualized for the systems which really does not require high amount of precisions or when economy is the major aspect and the BER performances can be tolerated. The search for a better modulation technique doesn‟t end here as the criterion for higher data rate communication is taking the lead in almost every area of communication and thus the ISI and BER realization become very important and crucial aspect for any future digital modulation technique. A Monthly Double-Blind Peer Reviewed Refereed Open Access International e-Journal - Included in the International Serial Directories

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REFERENCES [1] J. Sevenhans, B. Verstraeten, and S. Taraborrelli, “A contraction of modulator/demodulator Trends in Silicon Radio Large ScaleIntegration,” IEEE Commun. Mag., Jan. 2000Vol. 38, pp. 142–147. [2] Tsun-I Chien and Teh-Lu Liao, “Design of secure digital communication systems using chaotic modulation, cryptography and chaotic synchronization” Chaos, Solitons and Fractals 24 (2005), Pg. No. 241– 255. [3] Quadri, F. and Tete, A.D. “FPGA implementation of digital modulation techniques” IEEE International Conference on Communications and Signal Processing (ICCSP), 3-5 April 2013 Pg.No.913 – 917. [4] Chia-An Yeh and Yen-Shin Lai, “Digital Pulsewidth Modulation Technique for a Synchronous Buck DC/DC Converter to Reduce Switching Frequency” IEEE Transactions on Industrial Electronics Volume: 59 , Issue: 1 2012 , Page(s): 550 – 561. [5] R.Gandhiraj, Ranjini Ram and K.P.Soman, “Analog and Digital Modulation Toolkit for Software Defined Radio” International Conference on Communication Technology and System Design 2011 Procedia Engineering 30 (2012) Pg. No.1155 – 1162. [6] Dung Nguyen , Hobraiche, J. , Patin, N., Friedrich, G. and Vilain, J. “A Direct Digital Technique Implementation of General Discontinuous Pulse Width Modulation Strategy” IEEE Transactions on Industrial Electronics Volume: 58 , Issue: 9 2011 , Page(s): 4445 – 4454. [7] K.S. Chong, E. Zahedia,, K.B. Gan and M.A. Mohd. Ali, “Evaluation of the Effect of Step Size on Delta Modulation for Photoplethysmogram Compression” The 4th International Conference on Electrical Engineering and Informatics (ICEEI 2013) Procedia Technology 11 (2013) page no 815 – 822. [8] Hiroshi B.W. and Ramjee W.M., “Digital Communication”. Artech House, London, 2005,Pp.5-8. [9] Richardson J.F., „„Digital Modulation in Communication System’’. IEEE Explore,2002. [10] Di W. “Introduction to Communication System”, Penbrothers, New York, 2003, Pp. 316-318. [11] A.N. Rydbeck and Sundberg, “Continuous Phase Modulation System”IEEE transactions on communications (Legacy, pre-1988), vol. Com-29, no.3, pp. 210-225. [12] M.Simon, “A Generalization of minimum shift keying (MSK) –type signaling based jupon input data symbols pulse shaping,” IEEE transactions on communications vol. COM-24, no.8, pp.845-856. [13] W.Wei and Jerry M.Mandel, “A new Maximum-likelihood Method for Modulation Classification”, IEEE proceedings of ASILOMAR-29, pp 1132-1136.

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