Digital Communication Tutorial

Digital Communication is a combination of two different words, i.e., Digital and Communication. Here, the term "digital" refers to the discrete-time version representation of electronic signals or information signals, while the term "communication" refers to the process of exchanging information between two or more devices/entities. Therefore, the term "Digital Communication" refers to the process of exchanging information digitally.

This tutorial on Digital Communication is designed to help students and professionals working in the field of communication engineering. It covers all the concepts that provide idea on how the signals are digitalized, communicated, and why digitalization is needed in communication.

After completing this tutorial, we expect the readers will be able to understand the conceptual details involved in digital communication.

What is Communication?

Communication is defined as the process of exchanging data and information between two or more devices through a specific medium like wires or radio waves. A good communication of information is characterized by parameters like high accuracy, reduced noise, and low loss of signals.

In an effective communication, the received signal remains the same as the transmitted signal and convey the accurate information. In modern days, communication is a two-way process and allows for bidirectional sharing of information.

A typical communication has the following three main components −

Transmitter − It is the device that encode and sends the information.
Receiver − It is the reception end device used to receive and decode the information.
Communication Medium − It can be a wire or wireless component (like radio waves) that carries information from transmitter to receiver.

Problems with Ordinary Communication

The following are some major problems associated with the ordinary or analog communication −

Signal distortion
Delayed transmission of signals
Interference with or to neighboring communication mediums
Lower efficiency and accuracy, etc.

What is Digital Communication?

The process of exchanging information between different devices using digital (discrete-time) signals is referred to as digital communication. In other words, digital communication is the exchange of information among devices digitally.

Digital communication uses discrete time signals for representing data and information. It is the fundamental building block that forms backbone of internet technologies and modern telecommunication networks.

How The Digital Communication Works?

Digital communication involves the following three main working processes −

Encoding − Encoding is the process of converting original information signals like image, audio, video, etc. into a digital format. The key process involved in encoding is called sampling.
Transmission − Then, the encoded information signal is transmitted using various communication channels like coaxial cables, optical fibers, radio waves, etc.
Decoding − At the receiving end, the signal is decoded to retrieve the original information. The process involved in decoding is referred to as signal reconstruction.

Important Terms in Digital Communication

Some of the important terms and their meanings in context of the digital communication are given below −

Analog to Digital

It is defined as the process of converting analog signals into digital signals. This involves sampling, quantization, and encoding of continuous time signals to produce discrete time signals.

Pulse Code Modulation (PCM)

PCM is a modulation technique used to represent analog signals in digital format. In this modulation process, analog signals are sampled and quantized into discrete values and then encoded to obtain digital signals.

Sampling

Sampling is a process of measuring the amplitude of an analog signal at regular intervals to obtain a sequence of discrete values for digitalization. The interval at which the analog signal is sampled is referred to as sampling rate.

Quantization

The method of approximating the sampled values of an analog signal to nearest predefined values to make the samples suitable for digital encoding is known as quantization.

Differential PCM

Differential pulse code modulation (DPCM) is a modulation technique used in digital communication for signal encoding. It is a process of converting analog signals into digital signals. It uses the difference between successive samples, rather than absolute sample values, to reduce the bit rate.

Delta Modulation (DM)

Delta modulation is a simplified version of differential PCM. It is a signal encoding process used for converting analog signals into digital signals. In this technique, only 1-bit per sample is transmitted. This modulation technique is used where quality is not a primary importance like in voice information.

Line Codes

Line codes are defined as the patterns of signals used to represent digital data transmitted over a communication channel or written to a storage device.

Data Encoding Techniques

Data encoding techniques are nothing but methods of formatting analog signals into digital signals suitable for transmission over communication mediums.

Pulse Shaping

The process of changing the properties of waveform of a transmitted signal to optimize it is known as pulse shaping. It is primarily intended for reducing the bandwidth utilization and minimize the interference.

Digital Modulation Techniques

The techniques of modulating the digital message signal with a career signal for efficient transmission over a communication medium are referred to as digital modulation techniques.

Examples of digital modulation techniques include ASK (Amplitude Shift Keying), FSK (Frequency Shift Keying), PSK (Phase Shift Keying), and QAM (Quadrature Amplitude Modulation).

Amplitude Shift Keying (ASK)

ASK is a digital modulation technique in which the amplitude of the career signal is varied according to the digital data.

Frequency Shift Keying (FSK)

FSK is another digital modulation technique in which the frequency of the career signal is varied in proportion to the digital data.

Phase Shift Keying (PSK)

In PSK, the phase of the career signal is altered in accordance to the digital data.

Quadrature Phase Shift Keying (QPSK)

QPSK is an advanced version of the modulation technique PSK. It uses four possible phase shifts (0, 90, 180, or 270) in the career signal to modulate 2-bits at a time. This modulation technique allows for the transmission of multiple data bits simultaneously. This technique provides double data rate as compared to PSK.

Differential Phase Shift Keying (DPSK)

It is another version of PSK technique. In this method, the information is encoded by using the difference between the phases of successive samples, rather than absolute values.

In DPSK, the phase of the modulated signal is shifted with respect to the previous signal element.

M-ary Encoding

It is a digital modulation technique used for data transmission where one, two, or more bits are to be transmitted at a time in the form of a single signal. In M-ary, the symbol M represents multiple bits per signal. This modulation technique reduces the channel bandwidth and increases the data transmission efficiency.

Information Theory

Information theory is defined as a mathematical framework that deals with the study of quantification, storage, and communication of information. The primary aim of information theory is to provide data compression, error detection, and efficiency improvement in communication systems.

Source Coding Theorem

Source coding theorem is a principle in information theory that defines the statistical limits of lossless compression of data whose source is an independent identically-distributed random variable.

Channel Coding Theorem

Channel coding theorem is also known as Shannons theorem or Shannons limit. It is a principle in information theory that establishes the maximum data rate for communicating discrete data nearly error-free over a noisy communication channel.

Error Control Coding

Error control coding is defined as a technique in digital communication that controls the errors in data transmission over a noisy communication channel.

Spread Spectrum Modulation

Spread spectrum modulation is a method of transmitting digital signals over a wide range of frequencies. This modulation technique spreads the signals over a wider frequency band than the minimum required for efficient transmission of the signals. This technique is used for improving the security and interference immunity.

Advantages of Digital Communication

The key advantages of digital communication are listed below −

Digital communication is more accurate and reliable as compared to the traditional analog communication.
Digital communication provides faster way of conveying information over very large distances.
Digital communication also provides easy error detection and correction methods.
Digital communication is more immune to noise and interferences.
In long term, digital communication provides an inexpensive way of information exchange.
Digital communication allows sending information in various formats like voice, video, images, etc.

Disadvantages of Digital Communication

Apart from the advantages, digital communication also has certain disadvantages and limitations which are listed below −

Digital communication involves a complex structure of interconnected devices and consumes more power.
Digital communication requires wider bandwidth to provide high speed data transmission.
Due to large number of hardware components and high-speed data processing, digital communication is subjected to high power losses.

Applications of Digital Communication

Digital communication is used in a wide range of applications for information exchange in the form of digital signals.

Here are some common examples of applications of digital communication −

Digital signal, image, and video processing
Data compression
Speech and voice signal processing
Satellite communication
Digital audio transmission
Video conferencing
Mobile phone communication, etc.

Prerequisites to Learn Digital Communication

This tutorial is meant for absolute beginners. However, a basic understanding of electronic principles, basics of signal & systems, and mathematics will help you to better understand the concepts explained in the tutorial.

Who Should Learn Digital Communication?

This tutorial is a beginner friendly resource on digital communication. It is designed for absolute beginners who are interested in the basics of digital communication and who aspire to acquire the knowledge related to digital communication systems.

This tutorial can be used by undergraduate college students as well as practicing engineers as a reference.

FAQs on Digital Communication

In this section, we have collected a set of Frequently Asked Questions (FAQs) on Digital Communication followed by their answers −

Digital communication is nothing but an electronic communication system that allows exchange of data and information in the form of digital signals and tools.

The primary aim of digital communication is to efficiently transmit large amount of data and information over long distances with reduce noise and interference. This communication method is designed to provide an efficient, accurate, and reliable method for information exchange.

Some of the major risks of digital communication are as follows −

Unauthorized access to sensitive information.

Vulnerability to cyber threats and privacy concerns.

Accidental access to sensitive information.

Theft and manipulation of messages and information.

Illegal activities like sending fraudulent links or messages, etc.

The following are five very popular examples of digital communication −

Instant messaging like WhatsApp or messenger.

Video conferencing & meeting like Zoom or Google Meet.

Social media interactions like Facebook, Instagram, Twitter, etc.

Blogging like posting online articles.

Chatbots like customer service bots or ChatGPT.

The four main types of digital communications include (a) Email, (b) Social Media, (c) Instant Messaging, and (d) Video conferencing. Email is considered one of the first and most popular digital communication tool.

The three main elements of digital communication are given below −

Transmitter − It is the sender of the digital message.

Transmission channel − It is a medium through which digital messages travel to the destination.

Receiver − It is the receptor of the message.

Listed below are some of key features of the digital communication −

It provides point-to-point data transfer.

It provides efficient data transmission over long distances.

It enables high-speed and instant transmission and reception of data.

Digital communication enables real-time interactions.

It allows for sharing multimedia content.

Security concerns like data breaches, hacking, or other cyber threats are major issues associated with the digital communication. Theft of sensitive information is one of the major negative impacts of the digital communication.

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