Permutation-network-based optoelectronic path-history units for Viterbi decoders

摘要

A concept, believed to be new, is introduced that enables the design and implementation of the pathhistory (PH) unit of Viterbi decoders with permutation networks. The rationale behind this concept is that the trace-back operation in the PH unit is nothing but propagation of a signal traveling from the rightmost end to the leftmost end in the trellis diagram controlled appropriately by the decision bits. On the basis of this observation, an optoelectronic PH unit, which consists of directional coupler switches and registers, is proposed. This unit can be treated as a direct implementation of the trellis diagram of the underlying convolutional code and carries out the trace-back operation by propagating a photonic signal rather than an electronic signal through a given permutation network controlled by the decision bits. Hence the speed is inherently faster than the equivalent electronic version. Here both unfolded and folded versions of optoelectronic PH units are proposed.