Systems and Methods Using Digital Predistortion to Linearize Radio Transmitter Operation

A radio system comprising:

• an amplifier characterized by an amplifier transfer function for outputting a transmitter output signal during transmit time periods in response to an input signal;
• a digital predistortion system for linearizing the transmitter output signal with respect to the input signal and operable to:
• apply an inverse transfer function to the input signal before an input of the amplifier, the inverse transfer function being an inverse to the amplifier transfer function and characterized by an inverse transfer function polynomial having a set of coefficients;
• estimate a parameter of an intermodulation product in the transmitter output signal during a first transmit period to obtain a first estimated parameter value;
• in response to the first estimated parameter value, step a value of a selected coefficient of the set of coefficients of the inverse transfer function polynomial by a first step;
• in response to stepping the value of the selected coefficient of the inverse transfer function polynomial, estimate the parameter of the intermodulation product in the transmitter output signal during a second subsequent transmit time period to obtain a second estimated parameter value;
• and
• in response to a difference between the first and second estimated parameter values, step the value of the selected coefficient by a second step, wherein:
• if the first estimated parameter value is greater than the second estimated parameter value, a sign of the second step is equal to a sign of the first step;
• and
• if the first estimated parameter value is less than second estimated parameter value, the sign of the second step is opposite a sign of the first step.

A method of linearizing the output of a radio transmitter amplifier outputting a transmitter output signal during transmit time periods in response to an input signal, comprising:

• applying an inverse transfer function to the input signal before an input of the amplifier, the inverse transfer function being an inverse of a transfer function of the amplifier and characterized by an inverse transfer function polynomial having a set of coefficients;
• estimating a power of an intermodulation product of the transmitter output signal during a first transmit period;
• stepping a value of a coefficient of the set of coefficients of the inverse transfer function polynomial by a first step;
• estimating the power of an intermodulation product of the transmitter output signal during a second transmit period following the step in value of the coefficient;
• if the power of the intermodulation product decreases from the first to the second transmit periods, stepping the coefficient by a second step having a sign equal to the sign of the first step;
• and
• if the power of the intermodulation product increases from the first to the second transmit periods, stepping the coefficient by a second step having a sign opposite to the sign of the first step.