2009 first half of the database Systems engineering engineer Answers

The Hamming check code is to add a k check digit outside n data bits, thus forming a new code word of k+n bit, so that the code distance of the new code word can be larger evenly. The relationship between N and K is (1).

(1) A.2k-1>=n+k b.2k-1<=n+k c.n=k d.n-1<=k

"Answer" A

"Parsing" the basic knowledge of checking code.

The Hamming code is a multiple (duplex) parity-check error coding. It encodes the information in a logical way so that it can be checked for errors and corrected. All transmission codes used in the code are composed of the original information and the additional parity bits. Each of these parity bits is programmed at a specific location in the transmission code word. The following steps are required to derive and use a code word with a length of n bits:

(1) Determine the minimum number of check digits K:, write them into D1, D2 、...、 DK. Each check digit meets the different parity test requirements.

(2) The original information and the K check digit together to grow into; n+k bit new code word. Select the K check bit (0 or 1) to meet the necessary parity conditions.

(3) Make the required k parity check for the information received.

(4) If all the parity check results are correct, the information is considered to be error-free. If one or more errors are found, the wrong bits are determined uniquely by the results of these checks.

One of the basic considerations when seeking a sea-key is to determine the minimum number of check digits required K. Consider the information with a length of n bits, and if the K check digit is attached, the total length sent is n+k. A k parity check is performed in the receiver, and each check result is either True or false. The result of this parity check can be expressed as a K-bit binary word, which determines the maximum number of different states. One of these states must have all of its parity tests to be true, and it is the condition that determines the correct information. So the remaining (2k-1) state, can be used to determine the location of the error. The following relationships are then exported:

2k-l>=n+k.

2009 first half of the database Systems engineering engineer Answers