Reconfigurable trellis decoding of linear block codes

A class of methods for soft-decision decoding of linear block codes, referred to as reconfigurable trellis (RT) decoding, is presented. In RT decoding a reduced trellis (or tree) search is facilitated by carrying out the search on a reconfigured trellis (or tree) that corresponds to an equivalent code. The equivalent code is formed by reordering the received symbols according to their reliabilities. Consequently, the trellis reconfiguration is determined `on-the-fly´, but only a small portion of the trellis needs to be constructed, as guided by the reduced search. The search efficiency improves for channels where the soft-decisions provide a good indication of which symbols are in error. For example, using the M algorithm on an erasure channel, only a single survivor (i.e. M=1) is sufficient to attain maximum-likelihood decoding of maximum-distance codes. For more typical channels, we present simulation results and a detailed assessment of the number of metric and binary-vector operations for the M algorithm