Variable length tracebacks

摘要

A digital communication system including Viterbi decoder for tracing a path through a trellis of individual state information and method of operation are disclosed. The traceback determines a decoded symbol. The trellis of surviving branch data is stored in an array of registers. Operating the system includes initiating a first traceback from a storage register at a first symbol instant. The traceback traces a path back through the trellis a first predetermined number of symbol instants to determine a first decoded symbol. A second traceback is also initiated at the first symbol instant and traces a path back through the trellis a second predetermined number symbol instants to determine a second decoded symbol. The first traceback length may be greater than or less than the second traceback length. In another embodiment of the invention several tracebacks can be executed having a fixed traceback length, followed by other tracebacks having incrementally different traceback lengths. Such multiple tracebacks may be initiated in a single symbol instant. In yet another embodiment of the invention, selective ones of the decoded symbols are used by an equalizer to provide channel adaptation.