The performance comparison of the various partial response maximum-likelihood (PRML) systems for (1,7) RLL code and 8/9 code is studied. The bit-error rates of PR4ML, EPR4ML, EEPR4ML, PR (1,1,0,-1,-1) ML and PR (1,2,1,0,-1,-2,-1) ML systems are obtained by computer simulation. The relationships between the required SNR at the reading point to achieve a prescribed bit-error rate and the normalized linear density are also evaluated. Then, the performance comparison is made for FS-PRML system which can reduce the number of state in Viterbi decoder by half. It is shown that PR (1,2,1,0,-1,-2,-1) ML system and FS-PR (1,1,0,-1,-1) ML system for (1,7) RLL code exhibit the excellent performance.

View full abstract

In high density magnetic recording, the signal amplitude reduction called partial erasure results from the decrease in the spacing between magnetic transitions. It degrades the performance of PRML (Partial Response Maximum-likelihood) system which is considered to be an effective signal processing method in high density recording. In this paper, the error rate performance of several PRML systems including PRML system with a path feedback is obtained by computer simulation taking into account of partial erasure effect. And the excellent PRML systems in high density digital magnetic recording channel with partial erasure effect are clarified.

View full abstract

A rate 8/10 MSN code for a dicode channel is known in conventional researches. In this report, more than rate 8/10 MSN codes are constructed by using periodically time-varying trellis structures in Viterbi detection. It is useful to take these trellis structures in preserving same Eucledian free distance of proposed MSN code as conventional code's and restricting code's quasicatastorophic character to several intervals. By using proposed method, it is possible to design a higher rate code than a conventional MSN code effectively. In this report, a coding method for high rate MSN codes and evaluation of code's performance is shown.

View full abstract

In digital magnetic recording, discriminating method using neural networks was proposed and its feasibility of higher linear density capability was presented [MR94-16(1993-10), MR94-16(1994-07)]. The interesting noise characteristics that signals superimposed by high frequency sinusoidal or narrow width pulse noise can be discriminated as same as without noise was reported [MR95-4(1995-05)]. Furthermore, in this method, the computing speed of networks is very important for high transfer rate. If simultaneuos multi-bits discriminating is possible, it can be one solution. In this paper, the simult aneous 4bits discriminating networks are searched and discussed for the maximum achievable linear densities and noise characteristics.

View full abstract

In digital magnetic recording, a discriminating method using neural network was proposed and its feasibility of higher linear density capability was presented [MR93-31(l993-10), MR94-16(1994-07)]. In these simulation, four layer neural network of perceptron-type having two hidden layer was used. In this paper, the maximum achievable linear densities and learning characteristics was discussed comparing this four layer networks and usual three layer networks. these characteristics are different by learning method (5-5-1,5-3-1method [MR94-15(1994-07)] and sampling number of one bit waveform [NC94-53(1994-2)] and numbers of hidden layer elements. the results showed that four layer networks best for these two characteristics.

View full abstract

The signal-to-noise-ratio (SNR) performance of PR4ML system, EPR4ML system, and DFE/ML system are compared by computer simulation. This comparison takes into account the performance degradation due to asymmetric nonlinear distortion on MR-head read-back waveform. In addition, the performance stability of these system for signal resolution fluctuation are estimated quantitatively. The results show that DFE/ML system exhibits the best and most stable performance among these systems.

View full abstract

Some additional signal processing methods for magnetic disk drives are surveyed. Multi-channel recording using trellis codes might lead to even higher performance in the future. Partial erasure distortion accurately at high recording densities is discussed. A PR4ML operated at a 2 time slot mitigates the PE distortion at a high speed.

View full abstract