Error correction safeguards digital data, integrating extra bits to spot and fix inaccuracies. Its techniques vary, spanning basic checks to sophisticated coding. The discipline evolves with technological advancements like quantum computing, balancing system demands, projected errors, and processing capacity.
Types of Errors
Two fundamental types of errors can occur in data transmission: Bit errors (single bits flipped from 0 to 1, or vice versa) and burst errors (sequence of bits flipped).
Redundancy
The central concept in error correction is the use of redundancy. Additional bits, known as parity bits or check bits, are added to the data to help identify and correct errors.
Detection vs Correction
Error-detection techniques involve the receiver detecting that an error has occurred, but not necessarily correcting it. Error-correction techniques allow the receiver not only to detect an error but also to correct it automatically.
Error-Detection Codes
Some commonly used error-detection codes are parity checks, cyclic redundancy checks (CRC), and checksum methods. Each method provides a way of identifying errors but not correcting them.
Parity Check
Parity checks involve adding a single bit to make the total number of 1-bits either even (even parity) or odd (odd parity). A basic form of error detection, they can only identify an odd number of bit flips.
Cyclic Redundancy Check (CRC)
This is a more complex method where a sequence of check bits, known as a CRC, is appended to the end of the data block. These bits are derived from the binary division of the data bits by a predefined divisor, and they allow the detection of error bursts not longer than the CRC.
Checksum Methods
The checksum is a simple sum of the data bits. It’s effective for detecting errors in blocks of data but doesn’t identify the specific bit(s) that’s in error.
Error-Correction Codes
Some commonly used error-correction codes include Hamming codes, Reed-Solomon codes, and convolutional codes. They are designed not just to detect errors, but to correct them as well.
Hamming Codes
They use multiple parity bits to allow the identification and correction of single-bit errors. Hamming codes can correct any single-bit error or detect all single-bit and two-bit errors.
Reed-Solomon Codes
Reed-Solomon codes are block-based error correcting codes with a wide range of applications in digital communications and data storage. They can correct multiple random symbol errors, as well as burst errors.
Convolutional Codes
These codes work on bit streams of arbitrary length and use the method of ‘convolution’, which applies a function over the values of a sequence, to generate parity bits. They are commonly used in telecommunications, particularly in situations where the bit error rate is high.
Forward Error Correction (FEC)
FEC refers to the process where the sender encodes the message with an error-correcting code and the receiver uses this code to correct any errors. FEC is used when retransmissions are costly or impossible.
Automatic Repeat Request (ARQ)
Unlike FEC, ARQ involves the receiver sending a message back to the transmitter to request retransmission of data once an error is detected. There are several ARQ techniques such as Stop-and-Wait ARQ, Go-Back-N ARQ, and Selective Repeat ARQ.
