Technical Report CS0776

TR#:CS0776
Class:CS
Title: CONSTRUCTION OF ENCODERS WITH SMALL DECODING LOOK-AHEAD FOR INPUT-CONSTRAINED CHANNELS.
Authors: J.J. Ashley, B.H. Marcus and R.M. Roth
PDFCS0776.pdf
Abstract:

An input-constrained channel is defined as the set S of finite sequences generated by a finite labeled directed graph which defines the channel. A construction based on a result of Adler, Goodwyn and Weiss is presented for finite-state encoders for input-constrained channels. Let G = (V,E) denote a smallest deterministic presentation of S. For a given input-constrained channel S and for any rate p:q up to the capacity C(S) of S, the construction provides finite-state encoders of fixed-ratep:q that can be implemented in hardware with a number of gates which is at most polynomially large in |V|. When P/Q < C(S), the encoders have order \Leq 12|V|, namely, they can be decoded by looking ahead at up to 12|V| symbols, thus improving slightly on the order of previously-known constructions. Furthermore, when P/Q \Leq C(S) - ((\Log_2 E)/(2^P Q)) and S is of finite memory, the encoders can be decoded by a sliding-block decoder with look-ahead \Leq 2|V|+1.

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