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The rate of a code is inversely related to the query complexity, but the exact shape of this tradeoff is a major open problem. [8] [9] It is known that there are no LDCs that query the codeword in only one position, and that the optimal codeword size for query complexity 2 is exponential in the size of the original message. [8]
Say the code has codewords, then there are codewords that differ from a codeword by a burst of length . Each of the M {\displaystyle M} words must be distinct, otherwise the code would have distance < 1 {\displaystyle <1} .
Turbo coding is an iterated soft-decoding scheme that combines two or more relatively simple convolutional codes and an interleaver to produce a block code that can perform to within a fraction of a decibel of the Shannon limit.
A code with distance d allows the receiver to detect up to transmission errors since changing positions of a codeword can never accidentally yield another codeword. Furthermore, if no more than ( d − 1 ) / 2 {\displaystyle (d-1)/2} transmission errors occur, the receiver can uniquely decode the received word to a codeword.
Rate: 4/7 ~ 0.571: Distance: 3: Alphabet size: 2: ... all errors with a Hamming distance of 1 can be detected and corrected, which is the point of using a Hamming ...
The description above is given for what is now called a serially concatenated code. Turbo codes, as described first in 1993, implemented a parallel concatenation of two convolutional codes, with an interleaver between the two codes and an iterative decoder that passes information forth and back between the codes. [6]
Ignoring any lines going out of the picture, there are eight possible six-bit strings corresponding to valid codewords: (i.e., 000000, 011001, 110010, 101011, 111100, 100101, 001110, 010111). This LDPC code fragment represents a three-bit message encoded as six bits. Redundancy is used, here, to increase the chance of recovering from channel ...
Linearity guarantees that the minimum Hamming distance d between a codeword c 0 and any of the other codewords c ≠ c 0 is independent of c 0. This follows from the property that the difference c − c 0 of two codewords in C is also a codeword (i.e., an element of the subspace C), and the property that d(c, c 0) = d(c − c 0, 0). These ...