Chapter : Introduction to Digital Communication Engineering I, Semester, Engineering - Electronics and Communication Engineering (ECE) PDF Download

Introduction to Digital
Communications Engineering I

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

Overview

These lectures look at the following:
• Course introduction
• History of Communications
• Communications system
• Communication modes
• Methods of data communication
• Time constraints

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

• Transmission modes
• Analogue versus digital
• Baseband and bandpass
• Digital communications transceiver
• Conclusion
• Acknowledgement

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

Introduction

• Lecturer: Dr. Aoife Moloney
• Room: 426 Kevin St.
• Email: aoife.moloney@dit.ie
• Web: www.electronics.dit.ie/staff/amoloney

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

Course Introduction

• Course Code: COMM2108
• Assessment: 70 % Exam 30 % Lab
• Lectures: 2 hours/week
• Labs: 2 hours per week

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

Module Objectives

This module is designed to give an appreciation of the princi-ples of digital communications engineering. After completing this module you should:
• Be able to identify the main elements of a digital com- munications system.
• Understand source formatting, in particular, sampling, quantisation, signal to quantisation noise ratio.
• Be able to quantify the performance of baseband digital

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

systems in terms of bandwidth requirements, intersymbol interference and bit-error rates.

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

Syllabus

• Introduction to digital communications
• Source formatting
• Multiplexing
• Baseband communication: generation, transmission, de- tection

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

Textbooks

Recommended Reading:
• ‘PSpice for Digital Communications Engineering’, Paul Tobin, Morgan & Claypool 2007.
• ‘Communications Systems’ (4th Edition), Simon Haykin, Wiley 2001.
• ‘Communication Systems Engineering’ (2nd Edition), John G. Proakis and Masoud Salehi, Prentice Hall 2002.
• ‘Digital Communications: Fundamentals and Applica-

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

History of Communications

The highlights of the inventions which have lead to commu- nications as we know it today are listed below:
• 1440: Printing press - Gutenberg
• 1826: Ohm’s law - Ohm
• 1837: Line telegraphy invention - Gauss, Weber
• 1844: Line telegraphy patent - Morse
• 1858: 1st transatlantic cable (fails after 26 days)
• 1864: Electromagnetic radiation predicted - Maxwell

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

• 1866: Successful transatlantic telegraph cable (Valentia to Newfoundland)
• 1875: Telephone invented - Bell
• 1877: Phonograph invented - Edison
• 1887: Detection of radio waves - Hertz
• 1894: Wireless communication over 150 yards - Lodge
• 1895: Wireless telegraphy - Marconi
• 1897: Automatic telephone exchange - Strowger
• 1901: Transatlantic radio transmission - Marconi

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

• 1904: Diode valve - Fleming
• 1905: Wireless transmission of speech and music - Fesseden
• 1906: Triode valve - de Forest
• 1907: Regular radio broadcasts
• 1915: Trans. USA telephone line - Bell System
• 1918: Superheterodyne radio receiver - Armstrong
• 1919: Commercial broadcast radio - KDKA Pittsburg
• 1920: Sampling applied to communications - Carson
• 1926: Television invented - Baird (UK), Jenkins (USA)

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

• 1928: All electronic television - Farnsworth
• 1928: Theory of transmission of telegraph - Nyquist
• 1928: Information theory - Hartley
• 1933: FM demonstrated - Armstrong
• 1934: Radar - Kuhnold
• 1937: PCM (pulse code modulation) proposed - Reeves
• 1939: Commercial TV broadcasting - BBC
• 1943: Microwave radar used
• 1944: Statistical methods to describe noise and extract

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

signals - Rice
• 1945: Geostationary satellites proposed - Clarke
• 1946: ARQ (automatic repeat request) proposed - Du- uren
• 1948: Mathematical theories of communication - Shan-non
• 1948: Invention of transistor - Shockley, Bardeen, Brat- tain
• 1953: Transatlantic telephone cable

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

• 1955: Invention of laser - Townes, Schawlow
• 1961: Stereo FM transmission
• 1962: Satellite communication - TELSTAR
• 1963: Touch tone telephone - Bell System
• 1963: Geostationary communications satellite - SYN-COM II
• 1963: Error correction codes developed
• 1964: First electronic telephone exchange
• 1965: Commercial communications satellite - Early Bird

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

• 1966: optical fibre proposed - Kao, Hockman
• 1968: Cable TV
• 1970: Medium scale data networks - ARPA/TYMNET
• 1970: LAN, MAN, WAN
• 1971: ISDN proposed - CCITT
• 1972: First cellular mobile phone
• 1974: The Internet - Cerf, Kahn
• 1978: Cellular radio
• 1978: Navstar GPS (global positioning system)

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

• 1980: Fibre optic communications system developed - Bell System
• 1980: OSI 7 layer reference model - ISO
• 1981: HDTV (high-definition television) demonstrated
• 1985: ISDN basic rate access introduced - UK
• 1986: SDH introduced (SONET in USA)
• 1991: GSM (global system for mobile communications)
- Europe
• 1999: WAP (wireless application protocol)

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

There have been many many more inventions since 1999. As an exercise use the Internet to find as many recent telecom-munications inventions as you can.

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

Communications System

In its simplest form a telecommunications system consists of a transmitter, a channel, a receiver and two transducers.

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

Transducer

• Converts the input message into an electrical signal. Ex- amples of transducers include:
– Microphone – converts sound to electrical signal
– Camera – converts image to electrical signal
• A transducer is also used to convert electrical signals to an output message (or approximation of the input message), e.g., sound, images etc.

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

Transmitter

• Converts electrical signal to a form that is suitable for transmission through the transmission medium or channel.
• Generally matching of signal to channel is done by modulation.
• Modulation uses the information (message signal) to vary the amplitude, frequency or phase of a sinusoidal carrier,
e.g. amplitude/frequency modulation AM/FM.
• The transmitter also filters and amplifies the signal.

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

Receiver

• Recovers the message contained in the received signal
• Receiver demodulates the message signal
• Receiver filters signal and suppresses noise

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

Communication Modes

There are a few basic modes of communication:
• Point-to-Point: where one user wishes to communicate with one other user, or with a small group of nominated users. Examples include the telephone network or email.
Communication is normally two-way.
• Broadcast: Where one sender communicates with all capable receivers who cannot respond. the communica-tion is therefore normally one-way.
• Multicast: One sender communicates with a nominated

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

Methods of Data Transmission

There are a few basic methods of data transmission:
• Simplex: Data is transmitted in one direction only. The receiver cannot communicate with the sender.
• Duplex: Data transmission can take place in both di- rections simultaneously.
• Half-Duplex: Data transmission can take place in both directions but not at the same time.

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

Time Constraints

There are generally two sets of time restraints; real-time or time-lapse:

• Real-Time: Real-time communication is instant and data must be sent and received simultaneously. An example of this is the telephone network or two-way radio

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

communications. If a conversation is to be maintained there must be immediate interaction between the talkers. Delays will make the conversation difficult or impossible.

• Time-Lapse: Data may be received at any time after having been sent. Examples include email, radio and TV broadcasts. The time of receipt is not important.
Consider the case of radio and TV in more detail. It does not matter when a particular program is transmitted - time lapse is possible. However, once transmission begins it must be continuous and at a constant rate

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

during reception it appears as real-time.
There are also cases where time delay is not critical unless it is excessive e.g. downloading a file from a central server or from the Internet. A delay of a few seconds or even minutes is acceptable, but a delay of several hours is not acceptable.
In addition, components of a message should be received in the sequence in which they are sent (otherwise speech will be garbled). This may require that packets of data

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

Transmission Modes

All transmission is analogue, in the sense that physical quan- tities (voltage, current, electromagnetic radiation) must vary in a smooth way. However, the representation of the under- lying signals may be either analogue or digital.

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

Analogue versus Digital

Analogue

In the past most signals were generated, transmitted and re- ceived in analogue form i.e. as a sine wave or as a more complex signal which could be made up from a series of sine waves. This was done because speech is an analogue signal and it was easier to implement analogue electronic circuitry than digital. In a very simple system it is still easier to build in analogue. However, analogue has the following disadvantages:

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

• It is inflexible, in that to make any changes to the system all of the changes have to be made in hardware. This becomes more difficult and expensive as the system grows in size.
• It is prone to noise and distortion.
• Control and manipulation of signals is difficult. The mathematical treatment of analogue signals is relatively straightforward. An analogue signal is considered to have the form of a sine wave, or a combination of sine waves, the treatment of which is well established.

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

Digital

Computers deal in ‘1s’ and ‘0s’. Therefore communication between computers is a matter of transferring digital sequences between machines. The next step is to convert speech and other analogue signals into a digital format to permit a combined network. These days digital electronic circuitry is cheaper than analogue circuitry for the implementation of complex functions. Digital has the following advantages:

• Normally large scale digital systems are software controlled so that it is possible to make changes to the system

Introduction to Digital Communications Engineering ---------------------- Next Slide ------------ Dr. Aoife Moloney

in software and remotely.
• It is less prone to noise or distortion, a ‘1’ remains a ‘1’ and will not be mistaken for a ‘0’, unless there is an extreme level of distortion.
• If noise or distortion does occur, methods exist to determine that this has happened, and if appropriate to correct the error which has occurred.
• It is relatively easy to manipulate signals.
The mathematical treatment is not as straight forward as that for analogue.