In digital communications, a channel code is a broadly used term mostly referring to the forward error correction

Forward error correction

In telecommunication, information theory, and coding theory, forward error correction or channel coding is a technique used for controlling errors in data transmission over unreliable or noisy communication channels....

 code and bit interleaving in communication and storage where the communication media or storage media is viewed as a channel. The channel code is used to protect data sent over it for storage or retrieval even in the presence of noise (errors).

Overview

Channel codes are made up of two main type: convolutional codes and block code

Block code

In coding theory, block codes refers to the large and important family of error-correcting codes that encode data in blocks.There is a vast number of examples for block codes, many of which have a wide range of practical applications...

s. In practical communication systems, convolutional codes tend to be one of the more widely used channel codes. These codes are used primarily for real-time error correction and can convert an entire data stream into one single codeword. The Viterbi algorithm

Viterbi algorithm

The Viterbi algorithm is a dynamic programming algorithm for finding the most likely sequence of hidden states – called the Viterbi path – that results in a sequence of observed events, especially in the context of Markov information sources, and more generally, hidden Markov models...

 provided the basis for the main decoding strategy of convolutional codes. The encoded bits depend not only on the current informational k input bits but also on past input bits. Block code

Block code

In coding theory, block codes refers to the large and important family of error-correcting codes that encode data in blocks.There is a vast number of examples for block codes, many of which have a wide range of practical applications...

s tend to be based on the finite field arithmetic

Arithmetic

Arithmetic or arithmetics is the oldest and most elementary branch of mathematics, used by almost everyone, for tasks ranging from simple day-to-day counting to advanced science and business calculations. It involves the study of quantity, especially as the result of combining numbers...

 and abstract algebra

Algebra

Algebra is the branch of mathematics concerning the study of the rules of operations and relations, and the constructions and concepts arising from them, including terms, polynomials, equations and algebraic structures...

. Block codes accept a block of k information bits and return a block of n coded bits. Block codes are used primarily to correcting or detecting errors in data transmission

Data transmission

Data transmission, digital transmission, or digital communications is the physical transfer of data over a point-to-point or point-to-multipoint communication channel. Examples of such channels are copper wires, optical fibres, wireless communication channels, and storage media...

. Commonly used block codes are Reed-Solomon codes, BCH code

BCH code

In coding theory the BCH codes form a class of parameterised error-correcting codes which have been the subject of much academic attention in the last fifty years. BCH codes were invented in 1959 by Hocquenghem, and independently in 1960 by Bose and Ray-Chaudhuri...

s, Golay codes and Hamming code

Hamming code

In telecommunication, Hamming codes are a family of linear error-correcting codes that generalize the Hamming-code invented by Richard Hamming in 1950. Hamming codes can detect up to two and correct up to one bit errors. By contrast, the simple parity code cannot correct errors, and can detect only...

s.

Sometimes channel coding also refers to other physical layer

Physical layer

The physical layer or layer 1 is the first and lowest layer in the seven-layer OSI model of computer networking. The implementation of this layer is often termed PHY....

 issues such as digital modulation, line coding, clock recovery

Clock recovery

Some digital data streams, especially high-speed serial data streams are sent without an accompanying clock signal. The receiver generates a clock from an approximate frequency reference, and then phase-aligns to the transitions in the data stream with a phase-locked loop...

, pulse shaping

Pulse shaping

In digital telecommunication, pulse shaping is the process of changing the waveform of transmitted pulses. Its purpose is to make the transmitted signal better suited to the communication channel by limiting the effective bandwidth of the transmission. By filtering the transmitted pulses this way,...

, channel equalization

Equalization

Equalization, is the process of adjusting the balance between frequency components within an electronic signal. The most well known use of equalization is in sound recording and reproduction but there are many other applications in electronics and telecommunications. The circuit or equipment used...

, bit synchronization, training sequences, etc. Channel coding is distinguished from source coding

Source coding

In information theory, Shannon's source coding theorem establishes the limits to possible data compression, and the operational meaning of the Shannon entropy....

, i.e., digitizing

Digitizing

Digitizing or digitization is the representation of an object, image, sound, document or a signal by a discrete set of its points or samples. The result is called digital representation or, more specifically, a digital image, for the object, and digital form, for the signal...

 of analog message signals and data compression. The theory behind designing and analyzing channel codes is called noisy channel coding theorem

Noisy channel coding theorem

In information theory, the noisy-channel coding theorem , establishes that for any given degree of noise contamination of a communication channel, it is possible to communicate discrete data nearly error-free up to a computable maximum rate through the channel...

.

See also

• Channel capacity
  Channel capacity
  In electrical engineering, computer science and information theory, channel capacity is the tightest upper bound on the amount of information that can be reliably transmitted over a communications channel...
  
  
• Error correction and detection
• Forward error correction
  Forward error correction
  In telecommunication, information theory, and coding theory, forward error correction or channel coding is a technique used for controlling errors in data transmission over unreliable or noisy communication channels....
  
  
• Linear code
  Linear code
  In coding theory, a linear code is an error-correcting code for which any linear combination of codewords is also a codeword. Linear codes are traditionally partitioned into block codes and convolutional codes, although Turbo codes can be seen as a hybrid of these two types. Linear codes allow for...
  
  
• Locally decodable
  Locally decodable
  A locally decodable code is an error-correcting code that allows to decode a single bit of a message with high probability by only looking at a small number of bits of a possibly partially corrupted codeword....
  
  
• Noisy channel coding theorem
  Noisy channel coding theorem
  In information theory, the noisy-channel coding theorem , establishes that for any given degree of noise contamination of a communication channel, it is possible to communicate discrete data nearly error-free up to a computable maximum rate through the channel...
  
  
• Physical layer
  Physical layer
  The physical layer or layer 1 is the first and lowest layer in the seven-layer OSI model of computer networking. The implementation of this layer is often termed PHY....
  
  
• Source coding
  Source coding
  In information theory, Shannon's source coding theorem establishes the limits to possible data compression, and the operational meaning of the Shannon entropy....