Partial response QAM modem

A partial response QAM transmitter for generating a 5.times.5 partial response QAM transmit signal for a telephone voice channel, said transmitter comprising:

• first and second binary-to-ternary converter means for receiving a binary data input sequence having a data rate of 8000 BPS and for converting said sequence into a three-level sequence;
• first and second Class I partial response coder means respectively connected to the outputs of said first and second binary-to-ternary converter means for precoding and encoding said three-level sequence as a five-level Class I partial response coded signal;
• first and second lowpass shaping filters connected to the outputs of said first and second partial response coder means for converting said partial response coded signals into filtered signals having a bandlimited analog waveform;
• first modulator means for modulating the output of said first filter with an inphase carrier;
• second modulator means for modulating the output of said second filter with a quadrature phase carrier;
• and
• means for summing the outputs of said first and second modulator means to produce a QAM transmit signal having a bandwidth of approximately 2,667 Hz.

A partial response QAM transmitter for generating an 11.times.11 partial response QAM transmit signal for a telephone voice channel, said transmitter comprising:

• means for generating an input data sequence at a data rate of 16000 BPS;
• means for encoding sets of five bits and said input data sequence into pairs of six-level signals;
• first and second Class I partial response coder means for precoding and encoding said six-level signals as class I partial response coded signals;
• first and second shaping filters connected to the outputs of said first and second partial response coder means for converting said partial response coded signals into filtered signals having a bandlimited analog waveform;
• first modulator means for modulating the output of said first shaping filter with an inphase carrier;
• second modulator means for modulating the output of said second shaping filter with a quadrature phase carrier;
• and means for summing the outputs of said first and second modulator means to produce an 11.times.11 QAM transmit signal having a total bandwidth of approximately 3200 Hz.

A partial response QAM data transmission transmitter comprising:

• scrambler means for receiving serial binary data and converting said data into random distate data using a pseudo-random sequence;
• means for converting said random data to parallel streams of dibits;
• first and second level converter means located in an inphase channel and quadrature phase channel, respectively, for converting said parallel streams of dibits into N-level signals, where N .gtoreq. 3;
• first and second partial response coder means located in respective ones of said channels, for partial response coding said multilevel signals to produce partial response coded signals;
• first and second modulator means, located in respective ones of said channels, for modulating the partial response coded signals with inphase and quadrature carriers, respectively, to produce modulated inphase and quadrature partial response coded signals;
• and
• summing means for summing the modulated inphase and quadrature partial response coded signals.