Apparatus and method for synchronizing a digital modem using a random multilevel data signal

A receiver adapted to receive an input analog signal representative of data, comprising:

• sampling means for sampling the input signal to provide a digital signal;
• equalization means for adapting the equalization characteristics of the receiver to the equalization characteristics of the input signal;
• phase correction means for adapting the phase characteristics of the receiver to the phase characteristics of the input signal;
• detection means for detecting the data in the digital data signal;
• means for coupling the sampling means, equalization means, phase correction means, and the detection means to each other;
• error calculation means responsive to the digital signal for generating a system error signal;
• signal generation means responsive to the system error signal to provide a quality signal having a value dependent upon the degree of adaptation of the characteristics of the receiver to the characteristics of the input signal;
• control means responsive to the quality signal being within a first range of values for holding one of the equalization means and the phase correction means against adjustment and adjusting the other of the equalization means and the phase correction means to tend to adapt the characteristics of the receiver to the characteristics of the input signal;
• and
• said control means including means responsive to the quality signal being within said first range after a first period for adjusting the sampling means and means for thereafter holding said one means against adjustment and adjusting said other means to tend to adapt the characteristics of the receiver to the characteristics of the input signal.

A receiver for receiving an analog input signal comprising:

• adjustable means for adapting a plurality of characteristics of the receiver to the characteristics of the input signal, said receiver characteristics including phase, equalization, and timing characteristics;
• error calculator means for providing a system error signal which is related to the degree to which the characteristics of the receiver are adapted to the characteristics of the input signal;
• signal generation means responsive to the system error signal for providing a quality signal which is related to the value of the system error signal over an interval of time;
• first means responsive to the quality signal being within a first range of values for holding the equalization and timing characteristics of the receiver against adjustment and adjusting the phase characteristic of the receiver;
• and
• said first means including means responsive to the quality signal being within said first range of values after a first period for adjusting the timing characteristics of the receiver and then holding said equalization and timing characteristics against adjustment and adjusting the phase characteristic.

A receiver for receiving an analog input signal comprising:

• adjustable means for adapting a plurality of characteristics of the receiver to the characteristics of the input signal;
• error calculator means for providing a system error signal which is related to the degree to which the characteristics of the receiver are adapted to the characteristics of the input signal;
• first means responsive to said system error signal to adjust said adjustable means in accordance with either of a normal adjustment mode or a special adjustment mode, both of said adjustment modes tending to better adapt the characteristics of the receiver to the characteristics of the input signal;
• signal generation means responsive to the system error signal for providing a quality signal which is related to the value of the system error signal over an interval of time;
• said first means including means responsive to the quality signal being within a first range of values for inhibiting said normal adjustment mode and for adjusting said adjustable means in accordance with said special adjustment mode;
• said first means including means responsive to the quality signal being within a second range of values for enabling the normal adjustment mode and inhibiting the special adjustment mode, said second range of values being indicative of better adaptation of the characteristics of the receiver to the characteristics of the input signal than said first range of values;
• at least first and second of said characteristics of the receiver being adjustable in said normal adjustment mode;
• and
• said first characteristic being held against adjustment and second characteristic being adjustable in said special adjustment mode.

A method of adapting a receiver to the characteristics of an analog input signal, said method comprising:

• sampling the analog data signal to provide a digital data signal;
• substantially equalizing the digital signal using an equalizer having a plurality of taps;
• substantially phase correcting the digital signal;
• generating a system error signal which is related to the degree to which the characteristics of the receiver are adapted to the characteristics of the input signal;
• generating a quality signal which is related to the value of the system error signal over an interval of time;
• comparing the magnitude of the quality signal to a first reference level;
• continuing said step of phase correcting and setting said equalizer taps to a fixed value when the magnitude of the quality signal exceeds the magnitude of the first reference level;
• adjusting the sampling of the analog signal if the magnitude of the quality signal exceeds the magnitude of the first reference level after a first period;
• and
• continuing said step of phase correcting while maintaining said equalizer taps at said fixed value subsequent to said step of adjusting the sampling.