EETE 4220 Digital Communication & Switching Lecture Notes 2024-2025 PDF

EETE 4220 Digital Communication and Switching Semester I AY 2024-25 Class Lecture -7 Outcome #7-Understanding Channel Coding Course Lecturer :Lenin Joseph (LJ...

EETE 4220 Digital Communication and Switching Semester I AY 2024-25 Class Lecture -7 Outcome #7-Understanding Channel Coding Course Lecturer :Lenin Joseph (LJ) E&E Section. Dept. of Engineering. ACT Dec 24, 2024 1 OUTCOME #7 7. Understand the channel encoding -error detection and correction EETE 4220 Digital Communication & Switching -E&E Section. Dept. of Engine Dec 24, 2 ering. ACT 2024 BLOCK DIAGRAM OF DIGITAL COMMUNICATION SYSTEM INTRODUCTION In digital communication systems an optimum system might be defined as one that minimizes the probability of bit error. Error occurs in the transmitted signal due to the transmission in a non-ideal channel Noise exists in channels Noise signals corrupt the transmitted data CHANNEL ENCODER The channel encoder accepts the output digital signal of the source encoder and systematically adds extra bits to it. The extra bits or redundancy do not convey any information but helps the receiver to detect and / or correct some of the errors in the information bearing bits. Error control is accomplished by the channel coding operation. CHANNEL DECODER The Channel decoder recovers the information bearing bits from the coded binary stream. The added redundancy is taken away by the channel decoder. Error detection and possible correction is also performed by the channel decoder. ERROR CONTROL Error control is divided into two general categories: ERROR DETECTION Process of monitoring the data transmission and determining when errors have occurred. ERROR CORRECTION Process of correcting transmission errors by retransmission or forward error correction. ERROR DETECTION TECHNIQUES Vertical Longitudinal Cyclic Redundancy Redundancy Redundancy Checksum Checking(VR Checking(LR Checking(CR C) C) C) VERTICAL REDUNDANCY CHECKING (VRC)  Redundancy – duplicating each data unit for the purpose of detecting errors.  Redundancy Checking – adding bits to the data units to check for transmission errors.  Vertical Redundancy Checking (VRC) - the simplest type of error detection and is generally referred to as Character Parity.  With Character Parity (VRC), a single parity bit is added to each character to force the number of 1s in the code to either be an odd number (odd parity) or even number (even parity). Advantage:  Simplicity Disadvantage:  Detect only 50% of transmission error  When even numbers of bits are received in error, the parity checker will not be able to detect them correctly. LONGITUDINAL REDUNDANCY CHECKING (LRC) A redundancy error detection scheme that uses parity to determine if a transmission error has occurred within a message.  Also known as Message Parity.  With LRC, each bit position has a parity bit.  With LRC, even parity is generally used, whereas with VRC, odd parity is generally used.  Thebit sequence for LRC is often called Block Check Sequence (BCS) or Frame Check Sequence (FCS). ERROR CORRECTION Two basic types of error message: Lost message – message that never arrives at the destination or arrives but the damage is extensive and the message is unrecognizable. Damage message – message that is recognized at the destination but contains one or more transmission error. Two primary methods used for error correction: Retransmission Forward Error Correction REFERENCES Text Book Frenzel, L., Principles of Electronic Communication Systems, 3rd Ed. McGrawHill, 2008 Book References Sklar, Benard, “Digital Communications: Fundamentals and Application”, Prentice Hall, USA, 2001 Glover, Ian A / Grant, Peter M, “ Digital Communications”, Prentice Hall, UK, 2004 Proakis,John G,“ Digital Communications”, McGraw Hill Inc, USA, 2000 Wesolowski,Krzysztof, “Introduction to Digital Communication Systems”,2009 Web References\ e-library(s) https://ebookcentral.proquest.com/lib/momp/detail.action?docID=3011330 571, CD/DVD, Electronic Communication Systems: A complete Course, ACT Store THANK YOU