Fec scheme for encoding two bit-streams

Abstract

An encoding system is configured to allow data to be transmitted at one of two selectable bit-error-rate quality factors. The first bit-error-rate quality factor selection corresponds to the conventional ATSC FEC encoding systems, and the second bit-error-rate quality factor selection provides an ATSC-like FEC encoding scheme that substantially improves the bit-error-rate. The first quality factor selection effects a ⅔ trellis encoding, whereas the higher quality factor selection effects a ⅓ trellis encoding. Because the high-quality trellis encoding rate of ⅓ is half the lower-quality trellis encoding rate of ⅔, the data rate of this high-quality encoded bit-stream is half that of the conventional lower-quality encoded bit-stream. The ⅓ trellis encoding is effected using an ATSC-compatible encoding and a modified symbol mapping. The encoding scheme provides 2:1 data redundancy and the symbol mapping provides a maximum distance for the redundant encoding. By combining techniques that each decrease the likelihood of an uncorrectable error at the receiver, the substantial improvement in bit-error-rate can be achieved. At the receiver, a single trellis decoder with different metric tables is used to decode the two bit-streams, thereby providing substantial compatibility with ATSC-compatible receivers.