EFFICIENT SEQUENCE DETECTION FOR INTERSYMBOL INTERFERENCE CHANNELS WITH RUN-LENGTH CONSTRAINTS

This paper addresses the data detection problem of intersymbol interfe rence (ISI) channels with a specific modulation code-constraint known as the (d, k) run-length-limited (RLL) constraint, a popular modulatio n code-constraint for data storage channels as well as certain communi cation channels. A computationally efficient sequence detection algori thm is proposed which yields a performance close to that of the maximu m likelihood sequence detector when applied to such ISI channels. The proposed detector is derived as a high signal-to-mise ratio approximat ion to the delay-constrained optimum detector, one which minimizes the symbol error probability given a fixed decision-delay constraint. The proposed algorithm is essentially a fixed-delay tree search (FDTS) al gorithm with systematic ambiguity checking and is closely related to e xisting finite-depth tree search algorithms. It is observed that long critical error events common in uncoded ISI channels are eliminated by the RLL constraint. Based on this observation, we show that for some important RLL constrained channels, the proposed FDTS algorithm yields the same minimum Euclidean distance between distinguishable channel o utput sequences as the unconstrainted maximum likelihood sequence dete ctor.