Trellis codes for transition jitter | | Posted on:2002-03-22 | Degree:Ph.D | Type:Thesis | | University:Stanford University | Candidate:Wilson, Bruce Alexander | Full Text:PDF | | GTID:2468390011991395 | Subject:Engineering | | Abstract/Summary: |  PDF Full Text Request | | This thesis describes two pieces of work related to the special properties of data storage systems, when treated as a communications system. In particular, nonlinearity and non-stationary noise.; A novel procedure for characterizing the nonlinear read-back process is described. In this procedure, square-wave patterns are recorded over a range of linear densities. The resulting read-back signals should exhibit certain superposition properties if the read-back process were linear. The nonlinear response function of the read transducer distorts the read-back signal and makes the read-back process nonlinear. The inverse transfer function is modeled as a polynomial of fixed degree. The parameters of this model are chosen to most nearly linearize the read-back process, as measured using superposition properties of square-wave signals. The transducer transfer function can be inferred from the resulting estimate of the inverse transfer function. This estimate of the inverse transfer function can also be used directly to linearize the read-back process. An extension to this procedure is described for characterizing nonlinear readback from media with a soft keeper over-layer. Experimental results are shown.; Novel codes are described which combat signal-dependent noise in recording systems. In many recording systems the storage medium can only support a small number of discrete states. When this is the case most of the noise in the system is often associated with irregularities in transitions between these discrete states. We propose a trellis coded modulation scheme which makes the recording systems more robust to transition noise. Specifically, this family of codes makes it unlikely that transition jitter or transition erasure can cause one allowed sequence to be decoded as another allowed sequence. The codes are constructed using a convolutional encoder to constrain the sequence of recorded transition positions. This constraint mitigates against transition jitter. In addition the number of transitions in a block is constrained. This mitigates against transition erasure. This coding scheme was implemented on an experimental recording system comprised of a spin stand tester, digitizer and a software implementations of signal processing and detection algorithms. The proposed codes provide a significant gain over standard parity code schemes. | | Keywords/Search Tags: | Codes, Transition, Inverse transfer function, Read-back process, Systems | | PDF Full Text Request | Related items |
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