This document discusses error detection and correction. It explains that extra redundant bits are added to transmitted data to detect or correct errors. There are two main types of errors - single bit errors, where one bit is corrupted, and burst errors, where multiple contiguous bits are corrupted. The document introduces block coding, where the message is divided into blocks and redundant bits are added to each block to form codewords. It describes how error detection works by checking if the received codeword is valid. The two main types of error correction are also summarized - backward error correction requires retransmission, while forward error correction allows errors to be fixed without retransmission but uses more bandwidth.

1. ERROR DETECTION
AND CORRECTION
Moshrekul
Islam

2. BACKGROUND
 Some applications require that errors be
detected and corrected errors be detected
and corrected.
 Networks must be able to transfer data from
one device to another with acceptable
accuracy. For most applications, a system
must guarantee that the data received are
identical to the data transmitted. A
 Many factors can alter one or more bits of a
message. Some applications require a
mechanism for detecting and correcting
errors.
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Data can be corrupted during transmission.

3. 3
 Types of Errors
 Redundancy
 Block coding
INTRODUCTION
Let first discuss some issues related, directly or
indirectly, indirectly, to error detection and
correction.

4. 4
In a single-bit error, only 1 bit in the
data unit has changed.
TYPES OF ERRORS
Single Bit Error

5. 5
A burst error means that 2 or more
bits in the data unit have changed.
Burst Error
TYPES OF ERRORS

6. 6
To detect or correct errors, we need to
send extra (redundant) bits with data.
REDUNDANCY
The central concept in detecting or
correcting errors is redundancy.

7. 7
In block coding, we divide our message
message into blocks, each of k bits, called
datawords. We add redundant redundant
bits to each block to make the length n = k
+ r. The resulting resulting n-bit blocks are
called codewords.
BLOCK CODING
Use for error correction.
Process of error detection in block coding

8. ERROR DETECTION
Error Detection using block coding
How can errors be detected by using block coding?
If the following two conditions are met, the receiver
can detect a change in the original codeword.
1. The receiver has (or can find) a list of valid
codewords.
2. 2. The original codeword has changed to an
invalid one.
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9. 9
Backward Error Correction
• There are two ways to overcome the errors
Forward error correction
• Redundancy bits are added to the transmitted
information using predetermined information
ERROR CORRECTION
Error correction are two types

10. BACKWORD ERROR CORRECTION
 Known as Automatic Repeat Request(ARR)
 The receiver device sends a request to the
source device to re-send the data after
detecting the error or errors
 More often used because it requires less
bandwidth
 A return channel is required for backward
error correction
FORWARD ERROR CORRECTION
•This technique allows the receiver to detect
and correct errors without asking the send
error retransmission
•The bandwidth requirements higher but the
return channel is not needed
•Redundant data sent by transmitters also
called error-correction code
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ERROR CORRECTION