LIST OUTPUT VITERBI DECODING WITH CRC OUTER CODE FOR MULTI-RATE SIGNAL

摘要

A method and apparatus for decoding a frame of multi-rateencoded digital data which contains redundant informationprovided to validate the decoding operation. A frame of data isreceived which contains information bits and cyclic redundancycheck (CRC) bits. In accordance with the invention, the receivedframe is decoded and a check is conducted to determine whetherthe CRC bits correspond correctly for the decoded informationbits. If the decoded frame passes the CRC test process, thedecoded frame is provided to the user. However, if the decodedframe does not pass the CRC test, then at least one additionaldecoding process is performed on the received frame. In the firstexemplary embodiment of the present invention, on a failure ofthe CRC check, the data is decoded using a trellis decoder (224)and the data that yields the next most likely path through the trellisis selected. In a second illustrative embodiment, if the CRCtest fails, the trellis decoder (224) then identifies all paths havingmetrics within a predetermined threshold of a metric associatedwith the optimal path through the trellis. The CRC test is thenperformed on the decoded frame with respect to the suboptimalpaths (starting with the most likely path). If any of these pathspass the CRC check, the information bits are output by thedecoder (224). If not, an error is declared.