Partial-response maximum-likelihood: Difference between revisions

Revision as of 21:05, 9 October 2019

Revision as of 18:31, 12 October 2019

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In 1990, IBM shipped the first PRML channel in an HDD in the [https://en.wikipedia.org/w/index.php?title=History_of_IBM_magnetic_disk_drives&section=44 IBM 0681] (called Redwing during its development). The IBM 0681 was the last HDD product developed at the [[IBM Hursley]], lab. in the UK. It was full-height 5¼-inch form-factor with up to 12 of 130 mm disks and had a maximum capacity of 857 MB.

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The PRML channel for the IBM 0681 was developed in [[IBM Rochester]] lab. in Minnesota<ref>[https://ieeexplore.ieee.org/document/278677 J. Coker, R. Galbraith, G. Kerwin, J. Rae, P. Ziperovich, "Implementation of PRML in a rigid disk drive", IEEE Trans. Magn., Vol. 27, No. 6, pp. 4538-43, Nov. 1991]</ref> with support from the [[IBM Zurich]] Research lab. in [[Switzerland]].<ref>[https://ieeexplore.ieee.org/document/124468 R.Cidecyan, F.Dolvio, R. Hermann, W.Hirt, W. Schott "A PRML System for Digital Magnetic Recording", IEEE Journal on Selected Areas in Comms, vol.10, No.1, pp.38-56, Jan 1992]</ref> A parallel R&D effort at IBM San Jose did not lead directly to a product.<ref>[https://ieeexplore.ieee.org/document/104703 T. Howell, et al. "Error Rate Performance of Experimental Gigabit per Square Inch Recording Components", IEEE Trans. Magn., Vol. 26, No. 5, pp. 2298-2302, 1990]</ref>. A competing technology at the time was 17ML<ref>[https://www.researchgate.net/publication/224663211 A. Patel, "Performance Data for a Six-Sample Look-Ahead 17ML Detection Channel", IEEE Trans. Magn., Vol. 29, No. 6, pp. 4012-4014, Dec. 1993]</ref> an example of Finite-Depth Tree-Search (FDTS)<ref>[https://patents.google.com/patent/US5136593A/en R. Carley, J. Moon, "Apparatus and method for fixed delay tree search", filed Oct. 30th, 1989]</ref><ref>[https://ieeexplore.ieee.org/document/42527 R. Wood, "New Detector for 1,k Codes Equalized to Class II Partial Response", IEEE Trans. Magn., Vol. MAG-25, No. 5, pp. 4075-4077, Sept. 1989]</ref>. <br>

The IBM 0681 read/write channel ran at a data-rate of 24 Mbits/s but was more highly integrated with the entire channel contained in a single 68-pin [[Plastic leaded chip carrier|PLCC]] [[integrated circuit]] operating off a 5 volt supply. As well as the fixed analog equalizer, the channel boasted a simple adaptive digital 'cosine equalizer'<ref>[https://ieeexplore.ieee.org/document/1059216 T. Kameyama, S. Takanami, R. Arai, "Improvement of recording density by means of cosine equalizer", IEEE Trans. Magn., Vol. 12, No. 6, pp. 746-748, Nov. 1976]</ref> after the A/D to compensate for changes in radius and/or changes in the magnetic components.

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=== Post-processor architecture ===

Given the rapid increase in complexity with longer targets, a post-processor architecture was proposed, firstly for EPRML.<ref>[https://ieeexplore.ieee.org/document/281375 R. Wood, "Turbo-PRML, A Compromise EPRML Detector", IEEE Trans. Magn., Vol. MAG-29, No. 6, pp. 4018-4020, Nov. 1993]</ref>. With this approach a relatively simple detector (e.g. PRML) is followed by a post-processor which examines the residual waveform error and looks for the occurrence of likely bit pattern errors. This approach was found to be valuable when it was extended to systems employing a simple parity check<ref>[https://ieeexplore.ieee.org/document/917606 R. Cideciyan, J. Coker; E. Eleftheriou; R. Galbraith, "NPML Detection Combined with Parity-Based Postprocessing", IEEE Trans. Magn. Vol. 37, No. 2, pp. 714–720, March 2001]</ref><ref>[https://www.researchgate.net/publication/328870436 M. Despotovic, V. Senk, "Data Detection", Chapter 32 in ''Coding and Signal Processing for Magnetic Recording Systems'' edited by B. Vasic, E. Kurtas, CRC Press 2004]</ref>

=== PRML with Nonlinearities and Signal-dependent Noise ===