Elements of Digital Communications
Elements of Digital Communications by Prof. N. Sarkar
In the 1st chapter the essence of digital communication is briefly discussed in order that the reader obtains a special view of the subject matter. This includes similarities and differences that exist between analog and digital communication techniques in the form of block diagrams. Certain basic concepts emphasizing the figure of merit for comparison of different systems have been pointed out.
Principles of ‘Networking’ and ‘mobile-radio’ have been briefly discussed with a view to amplify the applications of digital communications. Signal theory and linear systems form the contents of chapter 2nd. As is well known that Fourier series, Fourier Integral, and also Fourier transform form the backbone of any electrical communication technique. Therefore, adequate coverage has been given towards the mathematics of Fourier techniques and its applications to linear system analysis.
Relationship between time domain and frequency domain is discussed at length. Spectral analysis of modulation and demodulation techniques, and Fast Fourier transforms (FFT) are also included. Transmitting of analog information using digital methods (PCM) form the contents of the 3rd chapter. Principles of sampling, quantizing, and coding and time-division-multiplexing (TDM) of anlog data are presented in this chapter. Performances of several practical communication system are compared with the performance of an ideal system. Pulse-code modulation (PCM), Delta modulation, Adaptive delta modulation, etc. have been treated.
Chapter 4th deals with random signal theory, which includes, probability theory, statistical averages, auto-correlation, cross-correlations, power spectral density etc. Calculations of probability of appearance of one letter symbol followed by another was also treated as an example towards formation of words, which carry information.
Chapter 5th discusses essentially Shannon’s theory of communication, which is named as Information theory and coding. Concepts of entropy as a measure of information, coding etc. are also highlighted. Source encoding theorem, channel coding theorem are among the six important theorems for which Shannon discussed. Shannon’s limits are also pointed out. Error control coding, block codes, BCH codes etc. forms the contents of 5th chapter.
Emphasis has been laid on convolutional codes, Viterbi algorithm and so on. Baseband data transmission, which many considers as the starting point of Digital Communication, forms the contents of 6th chapter. Data transmission at baseband perhaps form the most widely accepted mode of computer communication. One of the important problems addressed in this chapter is intersymbol interference (ISI) and pulse shaping.
Chapter 7th discusses digital carrier modulation which is also referred to as Bandpass data transmission. Because this form of communication is intimately connected to baseband data transmission, these are presented in consecutive chapters. This includes binary PSK, QPSK, M-ary PSK, frequencyshift-keying (FSK) etc. Minimum-shift-keying (MSK) is discussed and compared with QPSK. Differential QPSK technique is employed in the Telephone modems for computer communication. Comparison of various such systems are covered.
Chapter 8th considers another useful communication technique called the Spread-Spectrum modulation. Basic idea involved is to communicate in highly noisy environment. Communication in city environment, and secret communication in military are very good examples of application of spread spectrum techniques. PN-sequence, frequency-hopping, time-hopping etc. have been treated briefly. Code-division multiplexing is capable of supporting many users over the same channel (mobile) without any appreciable cross-talk and is made possible owing to use of Gold sequences.
Brief discussion in Telematics, Satellite communication, Optical fiber communication, form the contents of the 9th chapter.
Since hardware used is digital, an elementary form of discussion in Digital Electronics is included in the Appendix-A.
Properties of Fourier transform, and Hilbert transform are summarized in the Appendix-B.
Some useful Integrals, Error function, Gaussian probability function values, Trigonometric identities etc. form the other appendices. Delta function and its properties are discussed in the Appendix E.
A list of useful frequencies utilized in communication systems are also included. With this it is hoped that the reader will have enough exposure to the principles of Digital Communication.
For any further detail, the readers are referred to a number of good books and other references about 40 in number at the end.
Some of the important features described below have been introduced in aid of both the students and instructors :
1. Materials covered here include topics taught in most of our universities.
2. Introductory remarks in the beginning of each chapter familiarize the reader with clearly defined objectives. Summary at the end is intended to cover closing remarks, and also by reading it the reader will know what has not been covered.
3. Extensive use of solved examples (more than 170) and detailed solutions to introduce, amplify, and illustrate the concepts.
4. Home work problems with answers total more than 270.
5. Total number of figures exceed 300.
6. Each chapter contains Review questions. The reader can read the contents of each chapter and answer these questions progressively. Total number of such questions exceed 280.
7. Multiple choice questions.
Table of Contents:
♦ Introduction ♦ Characteristics of Instruments ♦ Errors in Measurement and their Analysis ♦ Indicating Instruments ♦ Electronic Measuring Instruments ♦ Generation and Analysis of Waveforms ♦ Cathode Ray Oscilloscope ♦ Electronic Counters ♦ Electronic Instruments ♦ Transducers ♦ Instrumentation for Measurement of Non-electrical Quality ♦ Data Acquisition System ♦ Power Measurement at High Frequencies ♦ Biomedical Measurements ♦ Intelligent Instrumentation ♦ Microprocessor and its uses in Instrumentation ♦ Measurements on Amplifiers and Receivers ♦ Appendix