UBC Theses and Dissertations
Signal and receiver design for high density digital magnetic tape recording Wood, Roger William
This thesis is concerned primarily with the improvement of data packing densities on magnetic tape. The concept of the 'magnetic recording channel' translates the thesis objectives into a concern for the maximization of channel data rate and minimization of error rate. A relatively comprehensive review provides background and indicates the present state of understanding for both magnetic recording and conventional communication channels. A helical-scan video-tape transport was selected as the vehicle for implementation and testing of signal and playback receiver designs. The recording channel was characterized by its response to balanced two-level record waveforms. The channel appeared approximately linear but was perturbed by moderate levels (-20dB) of additive noise as well as nonlinear behaviour. More serious degradations resulted from multiplicative noise (fading) manifest as extended (0.1 mm) regions of reduced playback level (dropouts). A prototype high-density recording system was constructed using non-return-to-zero signalling at 20 Mbit/s or 1.1 Mbit/m. The playback receiver comprised a fixed pre-filter followed by an adaptive seven-tap transversal, filter. System performance, measured in terms of 'burst' and 'isolated' error rates, was investigated as a function of various parameters including signal record level, equalizer complexity, and head-preamplifier coupling. Error control is essential in many applications and higher-order error statistics were-compiled in order to estimate the efficacy of error correction techniques. In particular, erasure detection and interleaved block coding proved to be useful techniques. The application of decision feedback was found to provide only marginal improvements in performance. However, decision feedback was shown to provide a useful method of correcting the d.c. channel null. Concluding remarks indicate the relevance of this work to narrower track systems and suggest likely emphases for future work.
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