A digital communication system including a 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. A trellis of branch origin data is stored in an array of registers (e.g., 28). The branch origin data associated with a symbol instant is an update instruction form a digital signal process (DSP) (e.g., 20) to the coprocessor (e.g., 30). A first predetermined traceback length is written to a traceback length register (e.g., 38). The first predetermined traceback length is small to minimize tracebacks cycling into branch origin data from a previous transmission burst. A traceback is initiated by the DSP (e.g., 20) providing the coprocessor (e.g., 30) a single traceback instruction. The Viterbi decoder alternates between update and traceback instructions. At a predetermined symbol instant, the traceback length is increased to a second predetermined length by over-writing the traceback length register (e.g., 38). The second predetermined length is selected relative to the predetermined symbol instant to assure tracebacks do not cycle into branch origin data from a previous transmission burst (e.g., 100). After all updates are complete, the update instruction is omitted and the traceback instruction repeatedly executed until all symbols from a transmission burst (e.g., 100) are decoded. IMAGE
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