| 摘要 |
An error control decoder (44) for use in decoding signals encoded with an M-ary convolutional code and a method for decoding such a code. The error control decoder includes a branch metrics module (46) that determines differences between the correlation values of each of eight possible symbols used to represent data encoded and the largest of these correlation values. An add-compare-select module (50) determines path metric values for each of 64 states by adding selected branch metric values to prior state metrics for the two possible paths that lead to a current state metric. The minimum path metric of the two is then assigned as a new state metric, and a logic level identifying the selected path metric is stored in a path history module (62). This procedure is repeated for each of the 64 states. A minimum state metric from the prior symbol period is determined and used to normalize the current state metrics to avoid overflow. After processing data for 36 symbol periods to form the initial path history, the data are decoded by tracing back through the path history to identify a state that most likely represents the binary data originally encoded. The error control decoder is disclosed in use in a spread spectrum communication system (20).
|
