Figure 4.4: PRBS generator for randomization.
4.2.2 ReedSolomon Encoder
The randomized data are arranged in block format before passing through the encoder and a single 0X00 tail byte is appended to the end of each burst. The implemented RS e n c o d e r i s d e r i v e d f r o m a s y s t e m a t i c R S ( N = 2 5 5 , K = 2 3 9 , T = 8 ) c o d e u s i n g G F ( 2 8 ) . T h following polynomials are used for code generator and field generator: e
G(x) = (x+ 0)(x+ 0)… (x+ p(x) = x8 + x4 + x3 + x2 + 1
The encoder support shortened and punctured code to facilitate variable block sizes and variable errorcorrection capability. A shortened block of k´ bytes is obtained through adding 239k´ zero bytes before the data block and after encoding, these 239k´ zero bytes are discarded. To obtain the punctured pattern to permit T´ bytes to be corrected, the first 2T´ of the 16 parity bytes has been retained.
4.2.3 Convolutional Encoder
implemented encoder has native rate of
polynomial in Equation
1/2, a constraint length of 7 and the generator to produce its two code bits. The generator is
shown in Figure 4.5.
G1 = 171OCT
G2 = 133OCT