LPOS symbol detection by soft-output combining of dual synchronous servo channels in tape drives

Abstract

On tape media, longitudinal position (LPOS) information is normally encoded in dedicated servo bands to allow rapid and accurate positioning of the tape medium and correct data placement on the tape, which is typically several hundred meters long. Robust detection of the longitudinal position of the tape is important to guarantee reliable placement of data as well as rapid navigation to a target tape location. We introduce a method for improving the LPOS symbol detection reliability based on the weighted combining of soft information provided by two independent servo channels. The soft information for each servo channel is generated from metrics computed using a matched-filter detector for the two hypotheses corresponding to the binary LPOS symbols. The weights are derived from a signal-to-distortion ratio measure that is obtained at the output of each servo channel to optimally combine the available information from the two servo channels. © 2011 Springer-Verlag.