Digital Communication and Switching - Lecture 7
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Questions and Answers

What is the goal of an optimum digital communication system?

To minimize the probability of bit error.

What are the two primary methods used for error correction?

Retransmission and forward error correction.

What is the simplest type of error detection?

  • Vertical Redundancy Checking (correct)
  • Checksum
  • Cyclic Redundancy Checking
  • Longitudinal Redundancy Checking

Which of the following is NOT a technique used for error detection?

<p>Forward Error Correction (D)</p> Signup and view all the answers

Character parity is the same as Vertical Redundancy Checking.

<p>True (A)</p> Signup and view all the answers

The channel encoder is responsible for detecting errors in the transmitted signal.

<p>False (B)</p> Signup and view all the answers

Longitudinal Redundancy Checking (LRC) uses even parity while Vertical Redundancy Checking (VRC) uses odd parity.

<p>False (B)</p> Signup and view all the answers

Error control is divided into two categories: error detection and error correction.

<p>True (A)</p> Signup and view all the answers

What does the channel encoder do with the output signal from the source encoder?

<p>It adds extra bits to the signal.</p> Signup and view all the answers

What is the purpose of the added redundancy in channel coding?

<p>To detect and/or correct errors in the transmitted data.</p> Signup and view all the answers

What happens to the added redundancy at the channel decoder?

<p>It is taken away.</p> Signup and view all the answers

What other name is used for Longitudinal Redundancy Checking?

<p>Message Parity (D)</p> Signup and view all the answers

Which method of error correction involves retransmitting the data?

<p>Retransmission (A)</p> Signup and view all the answers

Which error detection technique is considered to have the highest detection capabilities?

<p>Cyclic Redundancy Checking (A)</p> Signup and view all the answers

What is the primary purpose of a channel decoder?

<p>To recover the information-bearing bits from the coded binary stream.</p> Signup and view all the answers

What is the purpose of redundancy in data transmission?

<p>To help the receiver detect and/or correct errors in the transmitted data.</p> Signup and view all the answers

Adding extra bits to the data always increases the transmission time.

<p>True (A)</p> Signup and view all the answers

Give one example of a real-world application where error detection and correction techniques are used.

<p>Internet communication.</p> Signup and view all the answers

Flashcards

Optimum Digital Communication System

A digital communication system that minimizes the probability of bit errors.

Transmission Error

The degradation of a transmitted signal due to interference in the transmission channel.

Channel Noise

Unwanted signals in a communication channel that can corrupt the transmitted data.

Channel Encoding

A process that adds extra bits to a digital signal, increasing redundancy and enhancing error detection and correction capabilities.

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Redundant Bits

Bits added during channel encoding that don't carry information but aid in error detection and correction.

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Error Detection

The process of using redundant bits to detect errors in a received data stream.

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Error Correction

The process of correcting errors in a received data stream by retransmitting data or using forward error correction techniques.

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Lost Message

A data unit that is lost during transmission or arrives with significant damage, making it unrecognizable.

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Damaged Message

A data unit that is recognized at the destination, but contains one or more transmission errors.

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Retransmission

A method of error correction where the sender retransmits the entire message or a specific portion of it if an error is detected.

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Forward Error Correction (FEC)

A method of error correction that uses redundancy to correct errors without retransmission.

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Vertical Redundancy Checking (VRC)

A type of error detection technique that involves adding a parity bit to each character to ensure an odd or even number of 1s.

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Parity Bit

A single bit added to a character to achieve odd or even parity in the number of 1s.

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Character Parity

The simple type of error detection using parity bits for each character.

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Longitudinal Redundancy Checking (LRC)

A redundancy checking technique that uses parity bits to detect errors across a block of data.

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Block Check Sequence (BCS)

A bit sequence representing a calculated parity value for a block of data, used in LRC.

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Frame Check Sequence (FCS)

A bit sequence indicating the calculated parity for a data frame, used in LRC.

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Cyclic Redundancy Checking (CRC)

A type of error detection technique that uses mathematical calculations to detect and correct errors in data transmission.

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Checksum

A simple error detection technique that adds a checksum to a message, which is calculated based on the data bits.

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Channel Encoder

The device responsible for adding redundant bits to the digital signal before transmission.

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Channel Decoder

The device that removes the redundant bits and attempts to restore the original digital signal.

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Signal Decoding

The process of recovering the original digital signal from the coded binary signal in a communication system.

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Data Transmission

The process of transmitting data and identifying errors.

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Non-Ideal Channel

The communication channel is an environment where noise and distortions can interfere with the signal during transmission.

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Reliable Communication System

Error detection and correction techniques help design robust communication systems that are resistant to noise and interference.

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Error Control Methods

Different types of error control methods, such as CRC, VRC, and LRC, utilize various techniques to ensure data integrity.

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Error Control Importance

Understanding error control techniques is crucial for designing efficient and reliable communication systems.

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Error Control Selection

The process of selecting the best error control method for a given communication system depends on factors like noise levels, data rate, and desired reliability.

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Study Notes

Digital Communication and Switching - Lecture 7

  • Course: Digital Communication and Switching
  • Semester: I AY 2024-25
  • Lecture: 7
  • Outcome: Understanding Channel Coding
  • Lecturer: Lenin Joseph (LJ)
  • Date: Dec 24, 2024

Outcome #7: Understanding Channel Coding

  • Channel Encoding - Error Detection and Correction: The course focuses on understanding channel encoding for error detection and correction in digital communication systems.

Digital Communication System Block Diagram

  • A block diagram of a digital communication system was presented, showcasing the key components involved in the process.
  • Components include analog information source, A/D converter, source encoder, channel encoder, modulator, channel, demodulator, channel decoder, source decoder, D/A converter, and digital information sink.

Introduction

  • An optimal digital communication system aims to minimize bit errors.
  • Errors in transmission occur due to non-ideal channel characteristics, primarily noise.
  • Noise in the channel corrupts the transmitted data.

Channel Encoder

  • The channel encoder takes the source encoder's output and adds extra bits (redundancy).
  • Extra bits don't carry information but help the receiver detect or correct errors.
  • Error control through channel coding.

Channel Decoder

  • The channel decoder retrieves information bits from the coded binary stream.
  • Redundancy added by the encoder is removed.
  • Error detection and correction are performed.

Error Control

  • Error control is broadly categorized into two types:
    • Error Detection: Monitoring data transmission to identify errors.
    • Error Correction: Correcting transmission errors through retransmission or forward error correction.

Error Detection Techniques

  • Various techniques for error detection include:
    • Vertical Redundancy Checking (VRC)
    • Longitudinal Redundancy Checking (LRC)
    • Checksum
    • Cyclic Redundancy Checking (CRC)

Vertical Redundancy Checking (VRC)

  • VRC, also called character parity, is a simple error detection method that adds a parity bit to each character to make the total number of 1s either odd or even.
  • Only detects approximately 50% of transmission errors.
  • Not suitable for detecting multiple errors.

Longitudinal Redundancy Checking (LRC)

  • LRC, often called message parity, adds parity bits to each bit position in a message to help determine transmission errors.
  • Uses even parity.
  • Also known as Block Check Sequence (BCS) or Frame Check Sequence (FCS).

Error Correction Types

  • Lost Message: A message that never arrives, or arrives significantly damaged.
  • Damaged Message: A message arrives but with one or more errors.

Error Correction Methods

  • Retransmission: Re-sending the affected data.
  • Forward Error Correction: Methods to detect and correct errors without retransmission of data.

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

Description

This quiz covers the key concepts of channel coding for error detection and correction in digital communication systems. It includes an analysis of the digital communication system block diagram and aims to enhance understanding of minimizing bit errors during transmission. Perfect for students in their first semester of the Digital Communication and Switching course.

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