Patent ID: 7020828

Claim:
In an HDTV transmission system including a transmitter for transmitting a standard bit stream and a robust bit stream for receipt by an HDTV receiver device, an apparatus for encoding both bit streams in a backward compatible manner, said apparatus comprising: an enhanced coding block comprising a trellis encoder including a plurality of delay registers for delaying encoded bits of said both bit streams in response to control signals; said trellis encoder further comprising a plurality of multiplexers for multiplexing said both bit streams; a control unit tracking a bit stream type and generating the control signals for controlling the delay registers and the plurality of multiplexers of said trellis encoder according to the bit stream type; said enhanced coding block further comprising: a feedback input for accepting signals from a pre-coder of an A/53 trellis encoder; said A/53 trellis encoder operating in accordance with the ATSC A/53 standard; and a connection to the A/53 trellis encoder wherein a symbol mapper of the A/53 trellis encoder includes a subset of an A/53 trellis encoder symbol alphabet, said subset being associated with the robust bit stream for modulating a transmitter in a manner compatible with both standard and robust bit streams.