Digital Techniques Pdf

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01-Chap 1 InvestigTech 10/10/07 12:41 PM Page i. Investigative Uses of Technology: Devices,Tools, and Techniques. Reasons for Choosing Encoding Techniques. Digital data, digital signal – Equipment less complex and expensive than digital -to-analog modulation equipment. Analog data, digital signal – Permits use of modern digital transmission and switching equipme nt. Digital data, analog signal. DR & CR: TECHNIQUES AND STRATEGIES EVERYONECAN USE WCEC 2011 Dennis Bowman RT(R) Clinical Instructor Community Hospital of the Monterey Peninsula (CHOMP) Cabrillo College Our digital world has a new paradigm In the film/screen world, when a film was light there was nothing you could do to fix it. Hence, the motto was: when it doubt, dark it out.

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I am here sharing the pdf notes for Digital communication techniques as per the syllabus of electronics branch engineering students. This ebook for Digital communication techniques will help you in your studies for your semester examination and assist you in getting good marks.
The following topics are covered in these notes & ebook:
Module-I - Sampling Theorem, Low Pass Signal, Band Pass Signal, Signal Reconstruction, Practical Difficulties, The Treachery of Aliasing, The Anti-aliasing Filter, Application of Sampling Theorem, PAM, PWM and PPM Signal Generation and Detection.
Module-II - Pulse Code Modulation: Quantization of Signals, Uniform and Non-Uniform Quantization, The Compander, The encoder, Transmission Bandwidth and output SNR, Digital multiplexer, Synchronizing and Signaling, Differential PCM, Delta Modulation, Adaptive Delta Modulation, Output SNR, Comparison with PCM. Noise in PCM and DM: Calculation of Quantization Noise Power, Output Signal Power, and the Thermal Noise Power, Output SNR of PCM using different modulation techniques. Output SNR of DM.
Module-III - Principles of Digital Data Transmission: A Digital Communication System, Line Coding-Various line codes, Polar Signaling, ON-OFF Signaling, Bipolar Signaling, Pulse Shaping: Nyquist Criterion for zero ISI, Scrambling, Regenerative Repeater- Preamplifier, Equalizer, Eye diagram, Timing Extraction, Timing Jitter, A Base-band Signal Receiver, Peak Signal to RMS Noise output voltage ratio, The Optimum Filter, White Noise, The Matched Filter- Probability of Error of the Matched Filter, Coherent Reception.
Module-IV - Digital Modulation Technique: Generation, Transmission, Reception, Spectrum and Geometrical Representation in the signal space of BPSK, BFSK, Differentially- Encoded PSK, QPSK, Minimum Shifting Keying (MSK), M-ary PSK, M-ary FSK, Use of Signal Space to calculate probability of Error for BPSK and BFSK.

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.

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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:

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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.

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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°.

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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.

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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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