Blokkoder

Blokkoder is a term used in some Scandinavian contexts to refer to block codes, a family of error-correcting codes in information theory. In a blokkod, the input message is divided into blocks of k symbols and each block is transformed into a longer block of n symbols by adding redundancy. The code is characterized by its parameters (n, k) and its minimum distance d_min; the code can correct up to t = floor((d_min − 1)/2) symbol errors in each block.

Most blokkoder are linear, meaning the encoded block is a linear combination of the k message symbols. They are described by a generator matrix G (k×n) and a parity-check matrix H (n×(n−k)). Among common families are linear block codes (such as Hamming codes), cyclic block codes, BCH codes, and Reed-Solomon codes. Reed-Solomon codes operate over non-binary alphabets and are widely used because a single block can correct burst errors.

Decoding generally uses syndrome-based methods, maximum-likelihood decoding for small blocks, or iterative approaches for more complex codes. Block codes are contrasted with convolutional codes, which encode streams rather than fixed blocks, and with newer codes such as LDPC and turbo codes that approach channel capacity.

Blokkoder have broad applications in data transmission and storage. They protect data in CDs and DVDs, QR codes (where RS codes guard the data), error correction in RAID arrays, and digital communications standards.

See also: coding theory, error-correcting code, Reed-Solomon, Hamming code, BCH code. The term is used in Scandinavian languages as a direct translation of “block codes.”