1. check code and the code distance
Code distance: the minimum distance of any two of the codon.
Example: a code distance of 2 0000 1100
Check code
Parity
Detection code encoding only the odd bit errors, but the case can not be found even bit error
Hamming code
The position of the Hamming code check code must be in position 2 ^ n (n from zero, from the right, respectively 1,2,4,8,16 ......) is a non-information code position 2n
N-bit data is set, check code is k bits, the n and k must satisfy the condition 2 ^ k> = n + k + 1
Questions: Hamming code is an error correcting code, which is required to increase a number of parity check bits for the data, so that the values of the check codes are determined to certain blooming data, when an error check data, may be find out the dislocation according to changes in the value of the parity bit to correct the error. For 32-bit data, at least we need to add () in order to constitute a Hamming code check code
10-bit data, for example, Hamming code is represented as
D9D8D7D6D5D4P4D3D2D1P3D0P2P1 in which identification data bits Di, Pi represents a parity bit, the parity data bits P4, P3, P2 by the D9, D5 data bits from the checksum ()
A.3 B.4 C.5 D.6
A.P4P1 B.P4P2 C.P4P3P1 D.P3P2P1
Problem-solving ideas:
① Ruhai Ming code with formula
2^k>=32+k+1
2^5 = 32
2 6 = 64 ^ 6 so qualified, D is selected from
②D9 accounting data 14 bit checksum digits are 842
Therefore, the data D5 representing 10 bits, checksum bits to 82 selected from the group B
Cyclic Redundancy Check (CRC)