Capacity-approaching codes: can they be applied to the magnetic recording channel? (original) (raw)
Related papers
Capacity-Approaching Codes for the Magnetic Recording Channel
2002
Digital signal processing and coding are increasingly being recognized as a cost-efficient approach in achieving substantial areal density gains while preserving the high reliability of disk drives, although historically advances in head and media technologies have been the main driving force behind areal density growth. The recent advances in capacity-approaching codes hold the promise to push the areal density to the ultimate limit. In this article the various configurations regarding the interplay between soft detection and soft decoding through an iterative process, as it applies to the magnetic recording channel, are presented. In particular, the state of the art in turbo and turbo-like coding, including LDPC coding, is reviewed, and the serial concatenation of these coding schemes with inner generalized PR channels in a turbo equalization structure is described. Finally, an attempt is made to assess the performance and limitations of these AWGN channel-capacity-approaching codes when applied to the magnetic recording channel.
A Novel Error-Correcting System Based on Product Codes for Future Magnetic Recording Channels
IEEE Transactions on Magnetics, 2011
We propose a novel construction of product codes for high-density magnetic recording based on binary low-density parity check (LDPC) codes and binary image of Reed Solomon (RS) codes. Moreover, two novel algorithms are proposed to decode the codes in the presence of both AWGN errors and scattered hard errors (SHEs). Simulation results show that at a bit error rate (bER) of approximately 10-8 , our method allows improving the error performance by approximately 1.9dB compared with that of a hard decision decoder of RS codes of the same length and code rate. For the mixed error channel including random noises and SHEs, the signal-to-noise ratio (SNR) is set at 5dB and 150 to 400 SHEs are randomly generated. The bit error performance of the proposed product code shows a significant improvement over that of equivalent random LDPC codes or serial concatenation of LDPC and RS codes.
Performance comparison of selected DC-free codes for PR1-equalized magnetic recording channels
Proceedings of Icc 97 International Conference on Communications, 1997
Assuming the Lorentzian channel model and linearity, we compare the performance of various DGfree codes combined with PR1 signaling on the magnetic recording channel. In addition to several codes which have been presented in the literature, we consider two high rate DGfree codes (rates 8:Q and 16:18) which we have designed for the PR1 situation. Two types of Viterbi receivers are examined: one whose trellis is matched to the PR1 channel, and another whose trellis i s matched to the combined trellises of the PR1 channel and the code constraint. Our results demonstrate that high rate codes with a loose charge constraint (narrow spectral null) are to be preferred over lower rate codes with a tight contraint (wide null). We also demonstrate that the rate 16:18 code, which possesses both a high rate and a tight constraint (charge Q i s bounded as IQ1 5 4), offers the best performance among the codes considered. 'This work was supported by NSF under grant NCR-9409749. 'We use the notation p : q for code rate in the table to give explicit information on the data block size p and code block size q. In the next section, we will use the notation m/n for code rate, indicating the fraction p / q in lowest terms.
VLSI architectures for iterative decoders in magnetic recording channels
IEEE Transactions on Magnetics, 2001
VLSI implementation complexities of soft-input soft-output (SISO) decoders are discussed. These decoders are used in iterative algorithms based on Turbo codes or Low Density Parity Check (LDPC) codes, and promise significant bit error performance advantage over conventionally used partial-response maximum likelihood (PRML) systems, at the expense of increased complexity. This paper analyzes the requirements for computational hardware and memory, and provides suggestions for reduced-complexity decoding and reduced control logic. Serial concatenation of interleaved codes, using an outer block code with a partial response channel acting as an inner encoder, is of special interest for magnetic storage applications.
Polar codes for magnetic recording channels
2015 IEEE Information Theory Workshop (ITW), 2015
Polar codes provably achieve the capacity of binary memoryless symmetric (BMS) channels with low complexity encoding and decoding algorithms, and their finite-length performance on these channels, when combined with suitable decoding algorithms (such as list decoding) and code modifications (such as a concatenated CRC code), has been shown in simulation to be competitive with that of LDPC codes. However, magnetic recording channels are generally modeled as binary-input intersymbol interference (ISI) channels, and the design of polar coding schemes for these channels remains an important open problem. Current magnetic hard disk drives use LDPC codes incorporated into a turbo-equalization (TE) architecture that combines a soft-output channel detector with a soft-input, softoutput sum-product algorithm (SPA) decoder. An interleaved coding scheme with a multistage decoding (MSD) architecture with LDPC codes as component codes has been proposed as an alternative to TE for ISI channels. In this work, we investigate the use of polar codes as component codes in the TE and MSD architectures. It is shown that the achievable rate of the MSD scheme converges to the symmetric information rate of the ISI channel when the number of interleaves is large. Simulations results comparing the performance of LDPC codes and polar codes in TE and MSD architectures are presented.
Electronics
Although the joint source-channel coding (JSCC) system based on double protograph low-density parity-check (DP-LDPC) codes has been shown to possess excellent error performance over additive white Gaussian noise (AWGN) channels, it cannot perform well over one-dimensional inter-symbol-interference (OD-ISI) magnetic recording channels. In this study, a new JSCC system with a three-stage serially concatenated framework of Turbo equalization is firstly proposed for OD-ISI magnetic recording channels. Then, a modified joint protograph extrinsic information transfer (M-JPEXIT) algorithm is put forward to analyze the convergence-performance of the proposed system. By applying the M-JPEXIT algorithm, the channel codes are redesigned for this system to improve the error performance. Both the M-JPEXIT analysis and the bit-error-rate (BER) simulation results show the performance improvement of the proposed channel codes, especially in the water-fall region.
Iterative Detection-Decoding of Interleaved Hermitian Codes for High Density Storage Devices
Traditionally, Reed-Solomon (RS) codes have been employed in magnetic data storage devices due to their effectiveness in correcting random errors and burst errors caused by thermal asperities and inter-symbol interference (ISI). However, as storage densities increase the effect of ISI becomes more severe and much longer RS codes are needed, but this requires significantly increasing the size of the finite field. A possible replacement for RS codes are the one-point Hermitian codes, which are a class of algebraic-geometric (AG) code that have larger block sizes and minimum Hamming distances over the same finite field. In this paper, we present a novel iterative soft detection-decoding algorithm for interleaved Hermitian codes. The soft decoding employs a joint adaptive belief propagation (ABP) algorithm and Koetter-Vardy (KV) list decoding algorithm. It is combined with a maximum a posteriori (MAP) partial response (PR) equalizer and likelihoods from the output of the KV or the ABP algorithm are fed back to the equalizer. The proposed scheme's iterative detection-decoding behavior will be analyzed by utilizing the Extrinsic Information Transfer (ExIT) chart. Our simulation results demonstrate the performance gains achieved by iterations and Hermitian codes' performance advantage over RS codes.
Channel Coding Techniques for a Multiple Track Digital Magnetic Recording System
1994
In magnetic recording greater area) bit packing densities are achieved through increasing track density by reducing space between and width of the recording tracks, and/or reducing the wavelength of the recorded information. This leads to the requirement of higher precision tape transport mechanisms and dedicated coding circuitry. A TMS320 10 digital signal processor is applied to a standard low-cost, low precision, multiple-track, compact cassette tape recording system. Advanced signal processing and coding techniques are employed to maximise recording density and to compensate for the mechanical deficiencies of this system. Parallel software encoding/decoding algorithms have been developed for several Run-Length Limited modulation codes. The results for a peak detection system show that Bi-Phase L code can be reliably employed up to a data rate of 5kbits/secondltrack. Development of a second system employing a TMS32025 and sampling detection permitted the utilisation of adaptive equalisation to slim the readback pulse. Application of conventional read equalisation techniques, that oppose inter-symbol interference, resulted in a 30% increase in performance.
On reverse concatenation and soft decoding algorithms for PRML magnetic recording channels
IEEE Journal on Selected Areas in Communications, 2001
High-density magnetic recording systems require increasingly sophisticated signal processing techniques. In magnetic recording channels, the information bits are encoded by the concatenation of an outer nonbinary error correcting code (ECC) and an inner line code. Furthermore, the high intersymbol interference that characterizes the channel is controlled by "partial response" equalization. This paper presents a study on a better-integrated decoding procedure between the inner and outer codes. Inversion of the concatenated codes (reverse concatenation) allows the direct mapping of soft information from the partial response channel to the outer ECC. A simplified soft decoding technique, based on the use of erasures, is applied to two typical magnetic recording systems; performance curves are obtained by an analysis of the distributions of the reliability measures associated with incorrect and correct symbols.