Combined ecc/rll codes

Magnetic recording systems usually employ two types of codes: error correcting (ECC) codes and run length limited (RLL) codes. Here we investigate codes which are both ECC and RLL codes. Two new combined ECC/RLL trellis codes are presented. One is a 2-state (1, 3) code with Hamming distance 4 and the other is a 4-state (2, 6) code with Hamming distance 3. Each of these codes is decoded by a Viterbi decoder. A second coding scheme is discussed which employs a long constraint convolutional (ECC) code and a standard RLL modulation code. A single sequential decoder is employed to decode both codes by finding the best path through a single tree which describes both codes. Two RLL codes were utilized: a Miller (1, 3) code and a (2, 7) sliding block code. The complexity of the decoder for this scheme is much higher than the Viterbi decoder matched to the combined ECC/RLL trellis codes. However, a comparison of the performance of these competing schemes shows that the code with sequential decoding far outperforms the simpler trellis codes. The improved performance is due to the long constraint length of the code used for sequential decoding.