Chapter 8 : Error Detection

1. The exclusive OR(XOR) of any two valid codewords creates another valid codeword

2. Type of Error

2.1. Single bit Error : 1 bit in data unit has change

2.2. Bust Errror : 2 or more bits in data unit has change

3. Block Coding

3.1. 1. In a block coding, we divide our message into blocks, each of k bit is called datawords.

3.2. 2. Add r redundant bits to each block to make the length n = k +r. The resulting n-bit blocks are called codewords.

4. Linear Block Coding

4.1. Type of Linear Block Code

4.1.1. 1. Simple Parity Block Coding : a single bit error detection [ n = k + 1 = 2 ]

4.1.2. 2. Two-Dimensional Parity-Check Code

4.2. 1.The parity bit is calculated for each data unit

4.3. 2. The parity bit is organized into a table

5. Cyclic Code

5.1. If a code word is cyclically shifted (rotated), the result become another codeword

5.2. CRC can detect all burst errors that affect odd number of bits

5.3. CRC can detect all burst errors of length less than or equal to the degree of polynomial

6. Checksum

6.1. Based on the concept of redundancy

6.2. Can detect all errors involving an odd number of bits as well as most errors involving an even number of bits.

6.3. Cannot detect errors when one or more bits of segment are damaged and the corresponding bit or bits of opposite value in a second segment are also damaged.