12 research outputs found
Iterative decoding for magnetic recording channels.
The success of turbo codes indicates that performance close to the Shannon limit may be achieved by iterative decoding. This has in turn stimulated interest in the performance of iterative detection for partial-response channels, which has been an active research area since 1999. In this dissertation, the performance of serially concatenated recording systems is investigated by computer simulations as well as experimentally. The experimental results show that the iterative detection algorithm is not sensitive to channel nonlinearities and the turbo coded partial-response channel is substantially better than partial-response maximum-likelihood channels. The classical iterative decoding algorithm was originally designed for additive white Gaussian noise channels. This dissertation shows that the performance of iterative detection can be significantly improved by considering the noise correlation of the magnetic recording channel. The idea is to iteratively estimate the correlated noise sequence at each iteration. To take advantage of the noise estimate, two prediction techniques were proposed, and the corresponding systems were named noise predictive turbo systems. These noise predictive turbo systems can be generalized to other detector architectures for magnetic recording channels straightforwardly
CROSSTALK-RESILIANT CODING FOR HIGH DENSITY DIGITAL RECORDING
Increasing the track density in magnetic systems is very difficult due to inter-track interference
(ITI) caused by the magnetic field of adjacent tracks. This work presents a
two-track partial response class 4 magnetic channel with linear and symmetrical ITI; and
explores modulation codes, signal processing methods and error correction codes in order
to mitigate the effects of ITI.
Recording codes were investigated, and a new class of two-dimensional run-length
limited recording codes is described. The new class of codes controls the type of ITI
and has been found to be about 10% more resilient to ITI compared to conventional
run-length limited codes. A new adaptive trellis has also been described that adaptively
solves for the effect of ITI. This has been found to give gains up to 5dB in signal to noise
ratio (SNR) at 40% ITI. It was also found that the new class of codes were about 10%
more resilient to ITI compared to conventional recording codes when decoded with the
new trellis.
Error correction coding methods were applied, and the use of Low Density Parity
Check (LDPC) codes was investigated. It was found that at high SNR, conventional
codes could perform as well as the new modulation codes in a combined modulation and
error correction coding scheme. Results suggest that high rate LDPC codes can mitigate
the effect of ITI, however the decoders have convergence problems beyond 30% ITI
Reduced-complexity signal processing techniques for multiple-input multiple-output storage and wireless communication systems
Ph.DNUS-TU/E JOINT PH.D. PROGRAMM
Studies on interpolated timing recovery and external clock synchronization for magnetic recording channels
制度:新 ; 文部省報告番号:乙1909号 ; 学位の種類:博士(工学) ; 授与年月日:2004/10/28 ; 早大学位記番号:新387
Adaptive noise-predictive maximum-likelihood (NPML) data detection for magnetic tape storage systems
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Peer ReviewedPostprint (published version