Concatenated Error Correction Code - Applications

Applications

Although a simple concatenation scheme was implemented already for the 1971 Mariner Mars orbiter mission, concatenated codes were starting to be regularly used for deep space communication with the Voyager program, which launched their first probe in 1977. Since then, concatenated codes became the workhorse for efficient error correction coding, and stayed so at least until the invention of turbo codes and LDPC codes.

Typically, the inner code is not a block code but a soft-decision convolutional Viterbi-decoded code with a short constraint length. For the outer code, a longer hard-decision block code, frequently Reed Solomon with 8-bit symbols, is selected. The larger symbol size makes the outer code more robust to burst errors that may occur due to channel impairments, and because erroneous output of the convolutional code itself is bursty. An interleaving layer is usually added between the two codes to spread burst errors across a wider range.

The combination of an inner Viterbi convolutional code with an outer Reed–Solomon code (known as an RSV code) was first used on Voyager 2, and became a popular construction both within and outside of the space sector. It is still notably used today for satellite communication, such as the DVB-S digital television broadcast standard.

In a more loose sense, any (serial) combination of two or more codes may be referred to as a concatenated code. For example, within the DVB-S2 standard, a highly efficient LDPC code is combined with an algebraic outer code in order to remove any resilient errors left over from the inner LDPC code due to its inherent error floor.

A simple concatenation scheme is also used on the Compact Disc, where an interleaving layer between two Reed–Solomon codes of different sizes effectively spreads errors across different blocks.