| 摘要 |
A search path recovery mechanism for a sequential decoder employs a prescribed self-concatenated "Loeliger" convolutional code, that is either decodable by the sequential decoder for data recovery, or is decodable (although sub-optimally) by a Viterbi decoder as an adjunct to the sequential decoder to improve statistics during path recovery. The Viterbi decoder is incorporated in an alternate decoder which includes metric calculators, that compute branch metrics, that are alternately coupled to the Viterbi decoder, operating at twice the symbol rate. Using estimate bits from the Viterbi decoder, a syndrome former estimates the recovered state and generates an estimate of the validity of the recovered state. Their validity is verified by a path recovery detector, which operates as a zero error detection filter by summing a prescribed number of previous syndrome former outputs. When the sum of a consecutive number of syndrome former outputs is zero, the contents of the syndrome former are transferred to corresponding stages of the sequential decoder, to set the recovered path origination state for the sequential decoder. Once the sequential decoder has recovered to its correct origin state, a new origin state will not be required from the syndrome former unless path loss occurs.
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