Channel coding in the presence of bit robbing

A method for use in a transmitter which receives a stream of input data, the method comprising the steps of

• transmitting, during each of at least ones of a first plurality of signaling intervals, a respective signal representing a signal point selected from an identified one of a first plurality of signaling constellation subsets, and
• transmitting, during each of at least ones of a second plurality of signaling intervals, a respective signal representing a signal point selected from an identified one of a second plurality of signaling constellation subsets,
• at least ones of the first plurality subsets comprising a different number of signal points than at least ones of the second plurality subsets, each of said first and second plurality subsets being identified in response to a respective output of the same redundancy encoder, the redundancy encoder outputs being a function of at least a portion of said input data, and in each of said transmitting steps a different subset being identified for each different redundancy encoder output value.

A method for use in a transmitter which for each of a succession of signaling intervals, transmits over a communication channel a signal representing a selected one of a plurality of PCM quantization levels, said channel being of a type in which bit robbing occurs in particular ones of the signaling intervals, said transmitter including a trellis encoder which generates a succession of trellis encoder outputs which are a function of at least a portion of a stream of input data, said method characterized by the step of

• identifying, in response to each successive trellis encoder output, a subset of said PCM quantization levels from which said one PCM quantization level is to be selected for a particular one of said signaling intervals, said subset having a first number of said PCM quantization levels when the particular signaling interval is one in which bit robbing does not occur and having a second, smaller number of said PCM quantization levels when the particular signaling interval is one in which bit robbing does occur.

A transmitter which includes a trellis encoder, said trellis encoder generating a succession of trellis encoder outputs which are a function of at least a portion of a stream of data that is input to said transmitter, said transmitter comprising

• means for identifying, as a function of each successive trellis encoder output, an associated one of a plurality of subsets of PCM encoder levels, and
• means for transmitting over a communications channel a signal representing a particular one of the levels of the identified subset, each of said plurality of subsets having a first number of said PCM quantization levels when said signal is subject to being bit-robbed in said channel and a second, larger number of said PCM encoder levels when said signal is not subject to being bit-robbed in said channel.