Code rate
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The code rate or information rate of a forward error correction (FEC) code, for example a convolutional code, states what portion of the total amount of information that is useful (non redundant). The code rate is typically a fractional number. If the code rate is k/n, for every k bits of useful information, the coder generates totally n bits of data, of which n-k are redundant.
If R is the gross bitrate or data signalling rate (inclusive of redundant error coding), the net bitrate (the useful bit rate exclusive of error coding) is ≤ R•k/n.
For example: The code rate of a convolutional code may typically be 1/2, 2/3, 3/4, 5/6, 7/8, etc, corresponding to that one redundant bit is inserted after every single, second, third, etc, bit. The code rate of the Reed Solomon block code denoted RS(204,188) is 188/204, corresponding to that 204 - 188 = 16 redundant bytes are added to each block of 188 byte of useful information.
A few error correction codes do not have a fixed code rate -- rateless erasure codes.
