Yukinori Yamamoto

Bit Length of 57 nm Recording on Domain Wall Displacement Detection Disk Using Turbo Codes with Blue Laser

Turbo codes with max log maximum a posteriori probability (max-log-MAP) algorithm were experimentally applied to a domain wall displacement detection (DWDD) disk using a blue laser. The max-log-MAP algorithm is an approximation of the maximum a posteriori probability (MAP) algorithm; however, it reduces the amount of calculation and consumption of memory. An effective bit length of 56.5 nm recording was achieved using a partial turbo method with a parity bit rate of 1/17 at a bit error rate (bER) of 4 ×10-5 using a blue laser, although a bit length of 68.5 nm was the limit using a red laser. According to an analysis of the number of errors, the bER of the turbo method was found to depend on the number of consecutive 2-bit errors that occur with the dropout of the 2T pattern, and a jitter value less than 16% was necessary to keep the bER below 4 ×10-5 for the turbo method.

Turbo codes for a DWDD disc: bit length of 70nm recording with a red laser

Turbo codes, a partial turbo method and a serial turbo method, were experimentally applied to a Domain Wall Displacement Detection (DWDD) disk using a red laser. An effective bit length of 68nm recording was achieved by a partial turbo method with a parity bit rate of 1/17 at a bit error rate (bER) of 4x10-5 using a maximum a-posteriori probability (MAP) decoder, although a bit length of 80nm was the limit of the conventional partial response maximum-likelihood (PRML) method. It is presumable that the limit of the turbo decoding method for a DWDD disk depends on the number of consecutive 2-bit errors that occur with the disappearance of the 2T pattern. A max-log-MAP algorithm was introduced, instead of the usual MAP algorithm, to implement turbo codes in hardware, and an effective bit length of 69nm was achieved at a bER of 4x10-5.