Digital transmission system employing band limited analog medium with adaptive equalizer at transmitter

Claim 2

A transmission system having a transmitter and a receiver comprising, in combination, a source of multilevel PCM signals, a transversal equalizer at said transmitter connected to receive said PCM signals and predistort them, vestigial sideband modulation apparatus at said transmitter connected to receive said predistorted signals, an analog band limited transmission medium connected to the output of said modulation apparatus, vestigial sideband demodulation apparatus connected to receive said transmitted signals, an encoder connected to the output of said demodulation apparatus to generate digital signals, control apparatus responsive to said digital signals generated by said encoder to generate equalizer correction signals, and a signaling path connected between said receiver and transmitter to apply said equalizer correction signals to said equalizer.

Claim 3

A transmission system having a transmitter and a receiver comprising, in combination, a source of multilevel PCM signals, an n tap transversal equalizer at said transmitter connected to receive said PCM signals and predistort them, vestigial sideband modulation apparatus at said transmitter connected to receive said predistorted signals, an analog band-limited transmission medium connected to the output of said modulation apparatus, vestigial sideband demodulation apparatus connected to receive said transmitted signals, encoding apparatus connected to the output of said demodulation apparatus to generate digital output signals, polarity output signals, and error signals indicative of whether in reaching a level decision the encoding apparatus rounded the sample up or down, control apparatus responsive to said polarity and error signals to generate equalizer correction signals, a signaling path connected between said receiver and transmitter to transmit said equalizer correction signals back to said transmitter, memory and correction apparatus at said transmitter to store digital information representative of the setting of each of said n taps of said transversal equalizer and responsive to said equalizer correction signals to change said stored digital information and change the setting of each tap.

Claim 4

A transmission system having a transmitter and a receiver comprising, in combination, a source of multilevel PCM signals, an n tap transversal equalizer at said transmitter connected to receive said PCM signals and predistort them, vestigial sideband modulation apparatus at said transmitter connected to receive said predistorted signals, an analog band-limited transmission medium connected to the output of said modulation apparatus, vestigial sideband demodulation apparatus connected to receive said transmitted signals, encoding apparatus connected to the output of said demodulation apparatus to generate digital output signals, polarity output signals, and error signals indicative of whether in reaching a level decision the encoding apparatus rounded the sample up or down, control apparatus responsive to said polarity and error signals to generate equalizer correction signals, a signaling path connected between said receiver and transmitter to transmit said equalizer correction signals back to said transmitter, memory and correction apparatus at said transmitter to store digital information representative of the setting of each of said n taps of said transversal equalizer and responsive to said equalizer correction signals to change said stored digital information and change the setting of each tap.

Claim 5

Apparatus in accordance with claim 2 wherein said control apparatus responsive to said polarity and errors signals to generate equalizer correction signals comprises, a first shift register having n sTages, a first counter for establishing a predetermined time interval, a second shift register to which the error signals are applied, a second counter having k stages where k2 n, means responsive to the output of said first shift register and said second counter to enable an exclusive OR circuit connected to receive the output of said second shift register, a third counter connected to receive the output of said exclusive OR circuit for an interval determined by said first counter, and means connected to the output of said third counter to generate first, second and third predetermined signals when the count stored in said third counter is less than a first predetermined level, between a first and a second predetermined level, and greater than said second predetermined level respectively.

Claim 6

Apparatus in accordance with claim 2 wherein said memory and correction apparatus at the transmitter comprises in combination, a decoder to generate signals indicative of whether the equalizer control signals indicate that a particular equalizer tap setting is to be changed, memory apparatus to store information representative of the setting of each tap, a counter circuit responsive to the information stored in said memory apparatus and the output of said decoder to generate a digital signal representative of the proper setting of said particular tap, a digital to analog converter to convert said digital output of said counter to an analog signal, and a tap selection matrix responsive to said output of said analog to digital converter to adjust said particular tap of said equalizer.