Constellation multiplexed inband secondary channel for voiceband modem

A method of receiving main and secondary channel data in a synchronous data modem, the method comprising the steps of:

• receiving a plurality of synchronously transmitted constellation symbols;
• determining which of said plurality of constellation symbols are main channel symbols selected from a main channel constellation and which of said data symbols are secondary channel symbols selected from a secondary channel constellation, said secondary channel symbols and said main channel symbols being interleaved in time at periodic intervals so that said main channel symbols and said secondary channel symbols each carry synchronous data with the secondary channel data having a data rate which is a predetermined proportion of the data rate of said main channel data;
• processing said main channel constellation symbols according to a method for extracting data from said main channel constellation symbols;
• and
• processing said secondary channel constellation symbols according to a method for extracting data from said secondary channel constellation symbols.

A method for providing synchronization in a data modem, comprising the steps of:

• receiving a segment of data having length equal to that of a master frame having predetermined length, said master frame including a designated time period for transmitting secondary channel symbols from a secondary channel constellation;
• searching said segment for a first time period containing secondary channel symbols;
• and
• synchronizing said data modem receiver by setting said designated time period equal to said first time period.

An apparatus, comprising:

• main channel mapping means for generating symbols from a main channel constellation corresponding to main channel data;
• secondary channel mapping means for generating symbols from a secondary channel constellation corresponding to secondary channel data;
• selecting means for alternately selecting main channel and secondary channel symbols in a predetermined arrangement for transmission over a data channel;
• and
• transmitting means for transmitting said selected symbols.

An apparatus for receiving main channel and secondary channel data in a data modem, comprising:

• symbol receiving means for receiving main channel and secondary channel symbols;
• separating means for separating main channel symbols taken from a first constellation from secondary channel symbols taken from a second constellation, said main channel symbols and said secondary channel symbols being periodically interleaved in time;
• main channel decoding means for translating said main channel symbols to main channel data;
• and
• secondary channel decoding means for translating said secondary channel symbols to secondary channel data.

An apparatus for adjusting a characteristic of a data modem having a secondary channel and a main channel, said secondary channel being more immune to noise and other line disturbances than said main channel, said main and secondary channels being transmitted during main and secondary time intervals respectively, the apparatus comprising in combination;

• receiving means for receiving signals carrying said main and secondary channel;
• timing means for determining when said main and seconary channels respectively are being received;
• monitoring means for monitoring the quality of said received signals;
• and
• adjusting means, coupled to said monitoring means, for adjusting said characteristic of said receiving means while receiving either main or secondary channel when said signal quality is good and for adjusting said characteristic only during the time interval of receipt of said secondary channel when said signal quality is poor.

An apparatus for synchronizing a modem receiver to a modem transmitter, comprising in combination:

• receiving means for receiving one or more segments of data having length equal to that a master frame including a designated time period for transmitting secondary channel constellation symbols from a secondary channel constellation;
• searching means for searching said segment for a first time period containing a group of symbols separated by a predetermined phase characteristic and having average energy within a predetermined range;
• and
• synchronizing means for synchronizing said data modem receiver by setting said designated time period equal to said first time period.

A modulation-demodulation apparatus having a transmitter and a receiver comprising:

• said transmitter including a first and second mapping means,
• said first mapping means for grouping main-channel digital data into a plurality of main-channel bit groups and for selecting in response to each of said main-channel bit groups a main-channel complex-valued symbol from a main-channel symbol constellation having M complex-valued symbols so as to define a sequence of said selected main-channel symbols;
• said second mapping means for grouping secondary channel digital data into a plurality of secondary-channel bit groups and for selecting in response to each of said secondary-channel bit groups a secondary-channel complex-valued symbol from a secondary-channel constellation having N complex-valued symbols so as to define a sequence of said selected secondary-channel symbols, where M>N;
• said transmitter further including modulated carrier generating means for modulating a carrier signal by one of said selected symbols during each one of a plurality of symbol intervals;
• said transmitter further including a first switching means for repeatedly alternating between providing at least one said selected main channel symbol during a main-channel time period having at least one of said symbol intervals and at least one said selected secondary-channel symbol during a secondary channel time period having at least one of said symbol intervals;
• said receiver including symbol extracting means for receiving a modulated carrier signal having pairs of alternating carrier signal portions with one of said pair having been modulated by at least one received selected symbol from said main-channel symbol constellation of M complex-valued symbols and the other one of said pair having been modulated by at least one received selected symbol from said secondary channel symbol constellation of N complex-valued symbols, where M>N;
• said symbol extracting means including a second switching means for switching to a main receiver channel to receive said carrier signal portions modulated by received selected symbols from said main channel constellation and to a secondary receiver channel to receive said carrier signal portions modulated by said received selected symbols from said secondary channel constellation, said receiver channels each having signal extracting components suitable for operating on said carrier signal portions switched to said each receiver channel to extract said at least one selected symbol.

A modulation-demodulation apparatus having a transmitter and a receiver, comprising:

• a plurality of mapping means, each being operable to receive one of a plurality of sequences of binary data;
• each of said mapping means being operable for grouping said binary data allocated to said mapping means into a plurality of bit groups and for selecting in response to each said bit group a complex-valued symbol from a symbol constellation having a number of complex-valued symbols, said number being dependent upon a particular said mapping means;
• at least one of said constellations of one of said mapping means having a different said number of said complex-valued symbols than said number of said complex-valued symbols for one of the other said constellation of one of the other said mapping means;
• said transmitter further including modulated carrier generating means for modulationg a carrier signal by one of said selected symbols during each one of a plurality of symbol intervals;
• said transmitter further including a first switching means for sequentially providing during each one of a plurality of repetitive time cycles at least one said selected symbol from each of said mapping means to said modulated carrier generating means;
• said receiver including symbol extracting means for receiving a modulated carrier signal transmitted over a transmission medium, said modulated carrier signal having a repetitive cycle of a plurality of carrier signal portions with each of said carrier signal portions having modulated therein at least one selected symbol from one of a plurality of constellations of complex-valued symbols;
• and
• said symbol extracting means including a second switching means for switching between a plurality of receiver channels in response to said carrier signal portions, each of said receiver channels having signal extracting components suitable for operating on said carrier signal portions switched to said each receiver channel to extract said at least one selected symbol.