Algorithms for threshold level selection and decoder logic design in decision-aided symbol-by-symbol data receivers for magnetic recording applications

Symbol-by-symbol receivers comprise an important class of data receivers in digital magnetic recording applications. In systems where intersymbol interference (ISI) is high, these systems often use decision-aided decoding methods. A typical system employs threshold level detection followed by decoding logic. This paper presents an algorithm for selecting decoder threshold level settings and for generating the truth table for the decoding logic. By making use of all information available to the receiver, it is demonstrated that considerable reduction in the number of threshold levels required can be achieved in systems where the data encoding obeys run length limit constraints. It is also shown that selection of decode timing reference may have considerable influence on the number of threshold levels required. Application of the algorithm is demonstrated for several partial response signaling channels. A brief discussion is given on the similarities between the structure proposed by this paper and standard decision feedback equalizers