ccsds 131.0-b-2

CCSDS RECOMMENDED STANDARD FOR TM SYNCHRONIZATION AND CHANNEL CODINGTurbo Code: As used in this document, a block code formed by combining two componentrecursive convolutional codes. A Turbo code takes as input a block of k information bits.The input block is sent unchanged to the first component code and bit-wise interleaved (seeTurbo Code Permutation) to the second component code. The output is formed by the paritysymbols contributed by each component code plus a replica of the information bits.Turbo Code Permutation: A fixed bit-by-bit permutation of the entire input block ofinformation bits performed by an interleaver, used in Turbo codes.Virtual Fill: In a systematic block code, a codeword can be divided into an information partand a parity (check) part. Suppose that the information part is k symbols long (a symbol isdefined here to be an element of the code’s alphabet) and that the parity part is n symbolslong. A ‘shortened’ code is created by taking only S (S < k) information symbols as input,appending a fixed string of length k-S and then encoding in the normal way. This fixedstring is called ‘fill’. Since the fill is a predetermined sequence of symbols, it need not betransmitted over the channel. Instead, the decoder appends the same fill sequence beforedecoding. In this case, the fill is called ‘Virtual Fill’.CCSDS 131.0-B-2 Page D-4 August 2011