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Digital modulation techniques...

A Detailed Description of igital modulation techniques

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1. DIGITAL MODULATION TECHNIQUES Presented By: NIDHI BARANWAL MCA 3rd SEMESTER University of Allahabad
2. WHAT IS MODULATION • Modulation = Adding information to a carrier signal • The sine wave on which the characteristics of the information signal are modulated is called a carrier signal
4. MODULATION SYSTEMS
5. TYPES OF MODULATION  ANALOG MODULATION: 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  DIGITAL MODULATION: If the variation in the parameter of the carrier is discrete then it is termed as digital modulation technique
6. ANALOG MODULATION
7. DIGITAL MODULATION • In digital modulation , an analog carrier signal is modulated by a discrete signal • Digital modulation can be considered as digital- to-analog and the corresponding demodulation as analog-to-digital conversion • In digital communications, the modulating wave consists of binary data and the carrier is sinusoidal wave
8. DIGITAL MODULATION TECHNIQUES
9. AMPLITUDE SHIFT KEYING  In ASK, the amplitude of the signal is changed in response to information and all else is kept fixed  Bit 1 is transmitted by a signal of one particular amplitude. To transmit 0,we change the amplitude keeping the frequency constant
10. FREQUENCY SHIFT KEYING  In FSK, we change the frequency in response to information  one particular frequency for a 1 and another frequency for a 0
11. PHASE SHIFT KEYING  In PSK, we change the phase of the sinusoidal carrier to indicate information. Phase in this context is the starting angle at which the sinusoidal starts  One phase change encodes 0 while another phase change encodes 1.To transmit 0,we shift the phase of the sinusoid by 180
12. M-ARY MODULATION TECHNIQUE  In binary data transmission, send only one of two possible signals during each bit interval Tb  In M-ary data transmission, send one of M possible signals during each signaling interval T  In almost all applications, M = 2n and T = nTb, where n is an integer  Each of the M signals is called a symbol  These signals are generated by changing the amplitude, phase, frequency, or combined forms of a carrier.  Thus, we have: MASK MPSK MFSK MQAM
13. QUADRATURE PHASE SHIFT KEYING  Quadrature Phase Shift Keying can be interpreted as two independent BPSK systems , and thus the same performance but twice the bandwidth efficiency  The phase of the carrier takes on 1 of 4 equally spaced values where each value of phase corresponds to a unique pair of message bits
14. QUADRATURE AMPLITUDE MODULATION  If both the amplitude and the phase are varied proportional to the information signal, quadrature amplitude modulation results.  Combination of phase shifting and amplitude shifting
15. DIFFERENTIAL PHASE SHIFT KEYING  For the perfect detection of a phase modulated signal, the receiver needs a reference signal but if differential encoding and phase shift keying are made together at the transmitter the technique is called as Differential Phase Shift Keying  For the transmission of a symbol 1, the phase is unchanged whereas for transmission of symbol 0, the phase of the signal is changed by 180
16.  In DPSK, the phase shift is with reference to the previous bit transmitted rather than to some constant reference signal CONTD..
17. METRICS FOR DIGITAL MODULATION  POWER EFFICIENCY  Power efficiency is a measure of how much signal power should be increased to achieve a particular bit error rate (BER) for a given modulation scheme  Ability of a modulation technique to preserve the fidelity of the digital message at low power  Designer can increase noise immunity by increasing signal power  BANDWIDTH EFFICIENCY  Ability to accomodate data within a limited bandwidth  Tradeoff between data rate and pulse width  Easy to implement and cost-effective to operate.

GaussianWaves

Signal Processing for Communication Systems

Performance comparison of Digital Modulation techniques

Key focus : Compare Performance and spectral efficiency of bandwidth-efficient digital modulation techniques (BPSK,QPSK and QAM) on their theoretical BER over AWGN.

More detailed analysis of Shannon’s theorem and Channel capacity is available in the following book ● Wireless Communication Systems in Matlab (second edition) , ISBN: 979-8648350779 available in ebook (PDF) format and Paperback (hardcopy) format .

Simulation of various digital modulation techniques are available in these books ● Digital Modulations using Matlab : Build Simulation Models from Scratch , ISBN: 978-1521493885 ● Digital Modulations using Python ISBN: 978-1712321638

Let’s take up some bandwidth-efficient linear digital modulation techniques (BPSK,QPSK and QAM) and compare its performance based on their theoretical BER over AWGN. (Readers are encouraged to read previous article on Shannon’s theorem and channel capacity ).

Table 1 summarizes the theoretical BER (given SNR per bit ration – E b /N 0 ) for various linear modulations. Note that the E b /N 0 values used in that table are in linear scale [to convert E b /N 0 in dB to linear scale – use E b /N 0 (linear) = 10^(E b /N 0 (dB)/10) ] . A small script written in Matlab (given below) gives the following output.

Eb/N0 Vs. BER performance of various digital modulations over AWGN channel

The following table is obtained by extracting the values of Eb/N0 to achieve BER=10 -6 from Figure-1. (Table data sorted with increasing values of E b /N 0 ).

Capacity of various modulations their efficiency and channel bandwidth

is the bandwidth efficiency for linear modulation with M point constellation, meaning that η B bits can be stuffed in one symbol with R b bits/sec data rate for a given minimum bandwidth.

$\displaystyle{ B_{min}=\frac{R_{b}}{\eta_{B}}}$

is the minimum bandwidth needed for information rate of R b bits/second. If a pulse shaping technique like raised cosine pulse [with roll off factor (a)] is used then B min becomes

$\displaystyle{ B_{min}=\left( 1+a \right) \frac{ R_{b} }{ \eta_{B} }}$

Next the data in table 2 is plotted with E b /N 0 on the x-axis and η on the y-axis (see figure 2) along with the well known Shannon’s Capacity equation over AWGN given by,

$\displaystyle{C=W log \left(1 + \frac{C E_{b}}{W N_{0}}\right)}$

which can be represented as (refer [1] )

$\displaystyle{ \frac{E_b}{N_0} = \frac{2^ {\frac{C}{W}}-1}{\frac{C}{W}}}$

Matlab Code

[1] “Digital Communications” by John G.Proakis , Chapter 7: Channel Capacity and Coding.↗

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Digital modulation techniques

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Presentation on theme: "Digital modulation techniques"— Presentation transcript:

Chapter 2: Digital Modulation

EE578 Assignment #3 Abdul-Aziz.M Al-Yami October 25 th 2010.

Signal Encoding Techniques

Chapter : Digital Modulation 4.2 : Digital Transmission

1 Pertemuan 07 Teknik Modulasi Matakuliah: H0174/Jaringan Komputer Tahun: 2006 Versi: 1/0.

Data and Computer Communications Eighth Edition by William Stallings Lecture slides by Lawrie Brown Chapter 5 – Signal Encoding Techniques.

Data and Computer Communications

Data and Computer Communications Chapter 5 – Signal Encoding Techniques.

Chapter 5 – Signal Encoding and Modulation Techniques

Modulation of Digital Data 1.Digital-to-Analog Conversion 2.Amplitude Shift Keying (ASK) 3.Frequency Shift Keying (FSK) 4.Phase Shift Keying (PSK) 5.Quadrature.

1 Digital Data, Analog Signals (5.2) CSE 3213 Fall May 2015.

EE302 Lesson 21: Transmission of Binary Data in Communication Systems

S IGNAL E NCODING T ECHNIQUES Engr. Mehran Mamonai Department of Telecommunication.

William Stallings Data and Computer Communications 7th Edition

Teknik Modulasi Pertemuan 07 Matakuliah: H0484/Jaringan Komputer Tahun: 2007.

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Digital Modulation Techniques: Electronics Engineering Notes pdf ppt

Digital modulation techniques:.

Digital Modulation provides more information capacity, high data security, quicker system availability with great quality communication. Hence, digital modulation techniques have a greater demand, for their capacity to convey larger amounts of data than analog ones.

There are many types of digital modulation techniques and we can even use a combination of these techniques as well. In this chapter, we will be discussing the most prominent digital modulation techniques.

Amplitude Shift Keying:

The amplitude of the resultant output depends upon the input data whether it should be a zero level or a variation of positive and negative, depending upon the carrier frequency.

Amplitude Shift Keying (ASK) is a type of Amplitude Modulation which represents the binary data in the form of variations in the amplitude of a signal.

Following is the diagram for ASK modulated waveform along with its input.

Any modulated signal has a high frequency carrier. The binary signal when ASK is modulated, gives a zero value for LOW input and gives the carrier output for HIGH input.

Frequency Shift Keying:

The frequency of the output signal will be either high or low, depending upon the input data applied.

Frequency Shift Keying (FSK) is the digital modulation technique in which the frequency of the carrier signal varies according to the discrete digital changes. FSK is a scheme of frequency modulation.

Following is the diagram for FSK modulated waveform along with its input.

The output of a FSK modulated wave is high in frequency for a binary HIGH input and is low in frequency for a binary LOW input. The binary 1s and 0s are called Mark and Space frequencies .

Phase Shift Keying:

The phase of the output signal gets shifted depending upon the input. These are mainly of two types, namely BPSK and QPSK, according to the number of phase shifts. The other one is DPSK which changes the phase according to the previous value.

Phase Shift Keying (PSK) is the digital modulation technique in which the phase of the carrier signal is changed by varying the sine and cosine inputs at a particular time. PSK technique is widely used for wireless LANs, bio-metric, contactless operations, along with RFID and Bluetooth communications.

PSK is of two types, depending upon the phases the signal gets shifted. They are −

Binary Phase Shift Keying (BPSK):

This is also called as 2-phase PSK (or) Phase Reversal Keying . In this technique, the sine wave carrier takes two phase reversals such as 0° and 180°.

BPSK is basically a DSB-SC (Double Sideband Suppressed Carrier) modulation scheme, for message being the digital information.

Following is the image of BPSK Modulated output wave along with its input.

Quadrature Phase Shift Keying (QPSK):

This is the phase shift keying technique, in which the sine wave carrier takes four phase reversals such as 0°, 90°, 180°, and 270°.

If this kind of techniques are further extended, PSK can be done by eight or sixteen values also, depending upon the requirement. The following figure represents the QPSK waveform for two bits input, which shows the modulated result for different instances of binary inputs.

QPSK is a variation of BPSK, and it is also a DSB-SC (Double Sideband Suppressed Carrier) modulation scheme, which send two bits of digital information at a time, called as bigits .

Instead of the conversion of digital bits into a series of digital stream, it converts them into bit-pairs. This decreases the data bit rate to half, which allows space for the other users.

Differential Phase Shift Keying (DPSK):

In DPSK (Differential Phase Shift Keying) the phase of the modulated signal is shifted relative to the previous signal element. No reference signal is considered here. The signal phase follows the high or low state of the previous element. This DPSK technique doesn’t need a reference oscillator.

The following figure represents the model waveform of DPSK.

It is seen from the above figure that, if the data bit is LOW i.e., 0, then the phase of the signal is not reversed, but is continued as it was. If the data is HIGH i.e., 1, then the phase of the signal is reversed, as with NRZI, invert on 1 (a form of differential encoding).

If we observe the above waveform, we can say that the HIGH state represents an M in the modulating signal and the LOW state represents a W in the modulating signal.

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A Comparative Study of Various Digital Modulation Techniques

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, radiowave, 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...

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